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CHARACTERISTICS OF EXTREME-GAZE OCULAR FIXATION IN SPARSE VISUAL SURROUNDINGS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By Tyson L Brunstetter, OD., M.S.
*****
The Ohio State University 2000
Dissertation Committee: Approved by Nicklaus F. Fogt, OD ., PhD., Adviser Angela M. Brown, PhD . Adviser Mark A. BuIIimore, MCOptom, PhD. Physiological Optics Graduate Program Ronald Jones, OD., PhD. UMI Number 9971517
UMI*
UMI Microform9971517 Copyright 2000 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17. United States Code.
Bell & Howell Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT
The purpose o f this dissertatioa was to determine the characteristics of extreme-gaze ocular fibcation. This was accomplished by examining eye position and movements during fixation and scleral search coil slippage. Subject calibration of search coil equipment was also studied. Seven young, emmetropic subjects fixated an LED target monocularly in the dark. A bite bar was used to fix the head. Using search coil equipment, eye positions were collected as subjects fixated a 6 arcmin LED through nasal eye rotation angles (0“, 10°, 20°, 30° and 40°). A fbveal afterimage was used to monitor for stress-induced eccentric fixation, however none was detected. Even after correction for search coil slippage, temporal fixation lags increased with eye rotation angle, and the mean eye position measured at 40° significantly lagged the target (14.5 arcmin). Fixation precision did not appear to change over qre rotation angles. Overall, while measurements with the scleral search coil suggested a lag of fixation, target foveation occurred at all gaze angles. This imperfect representation of the fovea’s position by the search coil equipment may have been due to retinal stretching or crystalline lens tilting. Typical microsaccades occurred in all subjects, and end-gaze nystagmus occurred in two subjects during 40° eye rotations. High-magnification photography was used to dhectly measure slippage of the scleral search coü during nasal gaze angles. Search coil slippage was always in the temporal direction, progressively increased with eye rotation angle, and was significant during eye rotations o f 30° (11.9 arcmm) and 40° (23 J arcmm). The data suggest that the scleral lens and bulbar conjunctiva slide together during eye movements, and return to their original position as the eye returns to straight-ahead gaze.
ii At extreme angles, search coü calibrations horn a mechanical device differed fiom calibrations collected fiom human subjects. For search coü-based experiments vs^ere the eye is rotated laterally >10°, it may be more accurate to calibrate with subjects rather than the mechanical device. This would eliminate confotmding influences firom search coü slippage, improper target positioning and imperfect representation of the fevea’s position by the search
COÜ equipment.
lU Dedicated to the memory of my grandparents, Gerald R. and Mary E. Mooney.
IV ACKNOWLEDGMENTS
I would like to thank my advisor. Dr. Nick Fogt, for the volume of time and energy that he has invested into my education. However, this type o f sacrifice is not unusual for him; he always puts the student first Dr. Fogt has won numerous teaching awards for good reason. I would also like tothank Drs. Angela Brown, Mark BuIIimore, Ronald Jones and Ewen King-Smith for their support and suggestions, as well as for crucial advice on data analysis. Sincere appreciation is extended to the administration at the Naval Aerospace Medical Research Laboratory, especially to my Commanding and Executive Officers, Captain Glenn Armstrong and Commander Andrew Engle, respectively. Without their unwavermg support and their insistence that I keep pushing forward, this manuscript might never have been completed. VTTA
June 13,1971 ...... Bom - Warren, Ohio
1993 ...... B.S. Molecular Biology, Grove City College
1997 ...... OJ). Doctor of Optometry, The Ohio State University College o f Optometry
1997 ...... M.S. Physiological Optics, The Ohio State University Graduate School
1996-1997 ...... Research Assistant Eye Physiology Laboratory The Ohio State University College of Optometry
1997 - 1999 ...... Graduate Teaching and Research Associate The Ohio State University College of Optometry
1999 - present ...... Navy Optometrist / Primary hivestigator Naval Aerospace Medical Research Laboratory Naval Air Station Pensacola
VI PUBLICATIONS
1. Brunstetter TJ, Fink BA and Hill RM. What is the oxygen environment under an encapsulated segment bifocal contact len? JAm Optom Assoc 1999;70:641-6.
2. Hill RM, Brunstetter TJ and Fink BA. Complex oxygen pathways: Multi-layered contact lens systems and their transmissihilities. Invest Ophthalmol Vis Sci 1999;40(4):s9G5.
3. Brunstetter TJ and Fogt NF. Slippage of scleral search coils in extreme horizontal angles of gaze. Invest Ophthalmol Vis Sci 1999;40(4):s55.
4. Hill RM, Fink BA, Smith BJ and Brunstetter TJ. Physiological correlates of Dk/L: A developing model and its applications. Optom Vis Sci I998;75(12s):156.
5. Brunstetter TJ and Fogt NF. The accuracy and precision of extreme-gaze ocular fixation in sparse visual surroundings. Optom Vis Sci I998;75(12s):103.
6. Brunstetter TJ, Fink BA and Hill RM. The oxygen environment under an encapsulated segment bifocal RGP contact lens under static conditions. Optom Vis Sci 1997;74(l2s):94.
7. Brunstetter TJ. What is the oxygen environment under an encapsulated segment bifocal contact lens? Master of Science in Physiological Optics Thesis, Graduate School of The Ohio State University, Columbus, Ohio, June 1997.
FIELDS OF STUDY
Major Field: Physiological Optics
vu TABLE OF CONTENTS
A bstract...... ii D edication ...... iv Acknowledgments ...... v V ita...... vi List of Tables...... xi List of Figures ...... xv List of Programs ...... xx List of Slippage Plots ...... xxi List of Gaze Plots...... xxii Chapters: 1. Introduction ...... I 2. Historical Review ...... 5 2.0 Introduction...... 5 2.1 Direction of Gaze...... 5 2.1.1 Primary Line of Sight ...... 5 2.1.2 Eye Center of Rotation ...... 6 2.1.3 Positions of Gaze ...... 7 2.2 Foveal Fixation ...... 7 221.1 Miniature Eye Movements during Fixation ...... 8 2.2.2 Abnormal Fixation ...... 9 2.2 J Fixation and the Neural Integrator ...... 10 2.2.4 The Accuraty and Precision of Fixation in Extreme G aze 12 2.3 Objective Measurements of Eye Position and Movements ...... 15 23.1 Photography and Video ...... 16 233 Scleral Search Coil ...... 17 23.3 Sclaal Search Cod Slippage ...... 17 2.4 Afterimages ...... 19
vni 3. Methods and Materials ...... 35 3.0 Introduction...... 35 3.1 Subjects ...... 35 32 Photography Equipment Setup Procedures ...... 37 33 Search Coil Equipment Setup Procedures ...... 39 3.4 Experimental Procedures ...... 41 3.4.1 Photography Equipment Procedures ...... 42 3.42 Search Coil Equipment Procedures ...... 43 3.5 Data Overview ...... 46 4. Results...... 64 4.0 Introduction...... 64 4.1 Scleral Search Coil Slippage ...... 65 4.1.1 Distribution Shapes and Individual Variation ...... 65 4.12 Slippage Statistical Analysis ...... 67 42 Macro-Analysis of Extreme-Gaze Fixation ...... 69 42.1 Scleral Search Coil Intrinsic N oise ...... 70 422 Fixation Characteristics Before Correction for Search Coil Slippage ...... 72 422.1 Straight-Ahead Gaze ...... 72 4 2 2 2 Fixation in Nasal Gaze Without Afterim age ...... 72 422.3Fixation in Nasal Gaze With Afterimage ...... 74 423 Fixation Characteristics After Correction for Search Coil Slippage ...... 76 423.1 Straight-Ahead Gaze ...... 77 4 2 3 2 Fixation in Nasal Gaze Without Afterim age ...... 77 42.33Fixation in Nasal Gaze With Afterimage ...... 79 42.4 Extreme-Gaze Ocular Fixation Statistical Analysis ...... 80 4.3 Micro-Analysis of Extreme-Gaze Fixation ...... 82 43.1 Microsaccade Characteristics in Lateral G azes ...... 84 43.2 End-Gaze Nystagmus Characteristics in Lateral Gaze ...... 88 4.4 B lin k s...... 89 4.5 Human Calibrations in Scleral Search Coil Research ...... 90 5. Discussion...... 148 5.1 Scleral Search Coü Slippage ...... 148 5.1.1 Slippage Characteristics ...... 148 5.12 Slippage Theory ...... 149 5.1.3 Methods for Detecting Slippage ...... 150 52 Ocular Fixation in Eccentric Gaze...... 152 52.1 Accuracy and Precision of G aze ...... 152 522: Gaze Accuraqr Theory ...... 154 523 h/Gcrosaccade Characteristi<» ...... 159
K 5 2 A End-Gaze Nystagmus Characteristics ...... 161 5.3 Human Calibrations in Scleral Search Coil Research ...... 163 6. Conclusion ...... 173 6.1 Ocular Fixation in Eccentric Gaze...... 173 6 2 Scleral Search Coil Slippage ...... 175 Appendix A: hiformed Consent Form ...... 176 Appendix B: Computer Programs ...... 179 Appendix C: Slippage Plots ...... 251 Appendix D: Gaze Plots ...... 259 List of References ...... 323 UST OF TABLES
Table Page 2.1 Objective methods to assess eye position, and them respective resolution and Imear trackmg ranges...... 22
3.1 Subject enrollment criteria ...... 47
3 2 Pre-study examination sample profile ...... 48
33 Relevant data collected in mvestigatmg extreme-gaze ocular fixation characteristics ____ 49
3.4 Relevant data collected in investigatmg the feasibility of human calibrations in scleral search coil research ...... 50
4.1 Search coil position and standard deviation while viewmg the 0° LED target durmg each nasal ^ e rotation ...... 9 4
42^ Subject c-values and standard error of estimates describmg the quadratic regression fit o f relative search cod position over eys rotation angles ...... 95
43 Repeated measures ANOVA describmg relative search cod position as a function ofeye rotation anglev subject and the mteraction o f the tw o ...... 96
4.4 Tukey method of multiple comparisons comparmg overad relative scleral search cod positions measured over each nasal eye rotation ...... 97
43 Precision o f Station whde viewmg the (P LED target m straight-ahead gaze ...... 98
XI 4.6 Before correction for scleral search coü slippage; accuracy and precision of fixation w ithout the use of an afterimage while viewmg the 0° LED target during each nasal eye rotation ...... 99
4.7 Before correction for scleral search cod slippage: accuracy and precision of fhcation w ith the use of an afterimage while viewmg the 0° LED target durmg each nasal eye rotation ...... 100
4.8 After correction for scleral search coil slippage: accuracy and precision of fhcation w ithout the use of an afterimage while viewmg the 0° LED target during each nasal eye rotation ...... 101
4.9 After correction for scleral search cod slippage: accuracy and precision of fixation w ith the use of an afterimage whde viewmg the 0° LED target during each nasal eye rotation ...... 102
4.10 General Lmear Model ANOVA describmg ^ e position as a function o f subject, eye rotation angle, presence/absence of an afterün^e, the interaction of subject and afternnage an d the interaction of angle and afterimage ...... 103
4.11 General Linear Model ANOVA describmg eye position as a function of subject and eye rotation an g le ...... 104
4.12 Tukey method o f multiple comparisons comparing overad fhcation positions (both withoia and with the use o f an afternnage) whde the subject viewed the 0° target during each nasal ^ e rotation an g le ...... 105
4.13 Microsaccadic data coUected whde viewmg the 0° target in prmiary gaze ...... 106
4.14 Microsaccadic data coUected whde viewmg the 0" target durmg a 10° nasal qre rotation w ithout the use of an afternnage ...... 107
4.15 Microsaccadic data codected whde viewmg the 0° target durmg a20° nasal ^ e rotation w ithout the use of an afternnage ...... 108
xn 4.16 Microsaccadic data coUected while viewmg the 0" target during a 30° nasal eye rotation without the use of an aftmmage ...... 109
4.17 Microsaccadic data coUected whUe viewing the 0° target during a 40° nasal eye rotation without the use of an afternnage ...... HO
4.18 Microsaccadic data coUected whUe viewmg the 0° target durmg a 10° nasal eye rotation wAA the use of an afternnage...... HI
4.19 Microsaccadic data coUected whUe viewmg the 0° target during a 20° nasal eye rotation wAA the use of an afternnage ...... H2
420 Microsaccadic data coUected whUe viewmg the 0° target during a 30° nasal eye rotation wi/A the use of an afternnage ...... H3
421 Microsaccadic data coUected while viewmg the 0° target during a 40° nasal eye rotation wïA the use o f an afternnage ...... H4
422 General Linear Model ANOVA describing the duration o f microsaccades as a function of subject, qre rotation angle and presence/absence o f an afternnage ...... H 5
423 General Linear Model ANOVA describing the ampUtude o f microsaccades as a function of subject, eye rotation angle and presence/absence o f an afternnage ...... H6
424 General Linear Model ANOVA describmg the peak velocity o f microsaccades as a flmctioa o f subject, eye rotation angle and presence/absence o f an afternnage ...... 117
425 Characteristics of the 6st-phase component of end-gaze nystagmus ...... 118
426 Mean fixation position o f each subject durmg each temporal qre rotation angle whUe die head remamed fixed straight-ahead ...... 119
427 Mean fixation position ofprhnary gaze for each subject during each temporal head rotation an g le ...... 120
xui 42S The mathematical (üfiêrence between the respective data ofTables 4^7 and 4 2 6 ...... 121
5.1 Relevant positions and refiactive mdices for the #2 Guilstrand Simplified Schematic E y e ...... 166
XIV UST OF FIGURES
Figure Page 2.1 The lines ofsight do not cross at a single pomt, rather they form a caustic ...... 23
2.2 Main sequence plot of the saccade data of Zuber and S tark ...... 24
23 Zuber and Stark’s main sequence plot of microsaccades and saccades ...... 25
2.4 Eye position relative to the target center for Subject 1 and Subject 2 while gazing straight-ahead gaze ...... 26
23 Eye position relative to the target center for Subject I and Subject 2 while fixating 20® l e f t ...... 27
2.6 Eye position relative to the target center for Subject I and Subject 2 while fbcatmg40°left ...... 28
2.7 The relationship of true eye position to measured eye position for the scleral search coil equipment utilked m this « p erhnent ...... 29
2.8 Photographic method to monitor eys rotations ...... 30
2.9 Example o f a calculation of the amplitude o f an eye rotation based on the movement o f an ocular lanthnaiic...... 31
2.10 The scleral search coü after msertion onto the e y e ...... 32
2.11 The Helmholtz field coil cube ...... 33
XV 2.12 The mean search coil slipp%e for each nasal ^ e rotation angle ...... 34
3.1 The modified slit lamp equipment ...... 51
32 Photographic parallax erro rs ...... 52
32 Elhnination of photographic parallax errors is attained with a movable LED/pinhole and camera arrangement ...... 53
3.4 Position of the bite bar/forehead rest when set at 0® ...... 54
3.5 Position of the bite bar/forehead rest when set at 40“ ...... 55
3.6 Rowchart of the search coü equipment ...... 56
3.7 Bite bar equipment as viewed from the front o f the Helmholtz field c u b e ...... 57
3.8 Slippage of the scleral search co ü ...... 58
3 S Search coil slippage error plotted as a frmction o f bulbar conjunctiva radius o f curvature...... 59
3.10 Measurement of the eye position during ocular fixations, where the subject’s head is ahned straight-ahead an d stationary ...... 60
3.11 Measurement o f the eye position during ocular forations, whüe the subject’s head is rotated in random order twice throughout angles of 10°, 20°, 30“ and 40“ ...... 61
3.12 Measurement o f the eye position durmg ocular forations, whüe the subject’s head is rotated m random order twice throu^out angles of 10“, 20“, 30“ and 40“ ...... 62
3.13 Schematic o f the “plus sign” afterimage utilized m the “Head positioned at four difforent angles (wfrA an afternnage)” orpernnent described hr section 3 3 2 ...... 63
XVI 4.1 Flowcbait o f the Results chapter ...... 122
42 Overall search cofl. positions whfle viewmg the O ^tai^ during each nasal eye rotation angle ...... 123
43 Measured search cod positions as a function of data collection order ...... 124
4.4 Overall search cod positions whde viewing the 0° target durmg each nasal eye rotation angle ...... 125
4.5 Intrmsic noise of the scleral search cod equipment collected durmg calibration procedures ...... 126
4.6 The spectral density produced after 6 st fourier transformation of the mtrinsic search cod equipment noise seen in Figure 4J ...... 127
4.7 Corrected noise levels of the scleral search cod equipment after the intrinsic noise was band-filtered of its two dominant fiequencies ...... 128
4.8 Example ofeye position data before and after noise correction ...... 129
4.9 Second example of qre position data before and after noise correction ...... 130
4.10 Example of discarded subject eye position d a ta ...... 131
4.11 Overad fhcation positions whde subjects viewed the 0° target with head and eye straight-ahead ...... 132
4.12 Before correction for scleral search cod slippage: overad fixation positions withoia the use of an afternnage whde the subjects viewed the 0" target during each nasal eye rotation a n g le ...... 133
4.13 Before correction fi>r scleral search cod slippage: overad Scation positions with the use of an afternnage whde the subjects viewed the 0° target durmg each nasal eye rotation angle ...... 134
XVÜ 4.14 Overall fixation positions without the use o f an afterimage while the subjects viewed the 0° target during each nasal eye rotation angle ...... 135
4.15 Overall fixation positions with the use of an afternnage whüe the subjects viewed the 0® target durmg each nasal eye rotation angle ...... 136
4.16 Interaction plot of (subfect x eye rotation angle) ...... 137
4.17 Interaction plot of (subject x presence/absence of afterimage) ...... 138
4.18 Interaction plot of (angle x presence/absence o f afterimage) ...... 139
4.19 Mean ^ e positions for individual subjects during each nasal eye rotation angle ...... 140
420 Eye position relative to the target center for Subject 4 while fixatmg straight-ahead 141
421 Mean microsaccadic duration during each nasal q^e rotation an g le ...... 142
422 Mean microsaccadic amplitude during each nasal eye rotation angle ...... 143
423 Mean microsaccadic peak velocity during each nasal eye rotation angle ...... 144
424 Main sequence plot o f microsaccade data 6om this dissertation research, along with Zuber and Stark microsaccade and saccade d ata ...... 145
425 Relationship of ideal search coil position to measured search cod position for three calibration techniques ...... 146
426 Mean differences between two Human calibration techniques ...... 147
5.1(A) Path o f the ocular Inie o f sight through the Gudstrand Snnplified Schematic Eye; Comeal redaction ...... 167
5.1(B) Path o fthe ocular Ime o fsight throu^ the Gulbtrand Simplified Schematic Eye; Refiaction at the anterior len s ...... 168
xvü i 5.1(C) Path o f the ocular line of sight through the Guilstrand Snnplified Schematic Eye; Refiaction at the posterior lens ...... 169
5 2 Approxùnately 0.08 millimeters of foveal shear is necessary to mduce an apparent “fhcation lag” of 14.5 mmutes o f ar c ...... 170
53 The right eys must translate approximately 4 millnneters to mduce an apparait “fixation lag” of 143 minutes o f arc ...... 171
5.4 The crystalline lens must rotate approximately 3.6° to mduce an apparent “fhcation lag” of 143 mmutes o f ar c ...... 172
XIX U ST OF PROGRAMS
Program Page 1 Horizontal and vertical scleral search coil calibration program ...... 180
2 Accuracy and precision of ocular fbcation program ...... 1 9 1
XX UST OF SUPPAGE PLOTS
Plot Page 1 Measured search coQ slippage for each nasal eye rotation angle hi Subject I ...... 252
2 Measured search coil slippage for each nasal Q'e rotation angle in Subj'ect 2 ...... 253
3 Measured search coQ slippage for each nasal eye rotation angle hi Subject 3 ...... 254
4 Measured search coil slippage for each nasal eye rotation angle in Subj'ect 4 ...... ,...2 5 5
5 Measured search coQ slippage for each nasal eye rotation angle in Subject 5 ...... 256
6 Measured search coil slippage fbr each nasal eye rotation angle hi Subject 6 ...... 257
7 Measured search coQ slippage for each nasal eye rotation angle hi Subject 7 ...... 258
XXI UST OF GAZE PLOTS
Plot Page 1 Eye position relative to the LED target center for Subject I while gazing stra^ht-ahcad .. 260
2 Eye position relative to the LED target center fbr Subject 2 while gazing stra^ht-ahead ..261
3 Eye position relative to the LED target center fbr Subject 3 whüe gazing strait-ahead .. 262
4 Eye position relative to the LED target center for Subject 4 while gazing strait-ahead ..263
5 Eye position relative to the LED target center fbr Subject 5 whüe gazmg straight-ahead . 264
6 Eye position relative to the LED target center for Subject 6 whüe gazing straight-ahead . 265
7 Eye position relative to the LED target center fbr Subject 7 whüe gazmg straight-ahead ..266
8 Eye position relative to the LED target center for Subject 1 whüe gazing 10* le ft ...... 267
9 Eye position relative to the LED target center fbr Subject 2 whüe gazing 10* le ft ...... 268
10 Eye position relative to the LED target center for Subject 3 whüe gazmg 10* le ft ...... 269
11 Eye position relative to the LED target center for Subject 4 whüe gazmg 10* le ft ...... 270
12 Eye position relative to the LED target center for Subject 5 whüe gazmg 10* le ft ...... 271
13 Eye position relative to the LED target center fbr Subject 6 whüe gazing 10* le ft ...... 272
14 Eye position relative to the LED target center fbr Subject 7 whüe gazmg 10* le ft ...... 273
15 Eye position relative to the LED target center fbr Subject I whüe gazmg20* le ft ...... 274
16 Eye position relative to the LED target center fbr Subject 2 whüe gazmg 20* le ft ...... 275
17 Eye position relative to the LED target center for Subject 3 whüe gazmg 20* le ft ...... 276
18 Eye position relative to the LED target center for Subject 4 whüe gazmg 20* le ft ...... 277
19 Eye position relative to the LED target center for Subject 5 whüe gazmg 20* le ft ...... 278
xxn 20 Eye posMoii relative to the LED target center for Subject 6 while gazing 20* le ft ...... 279
21 Eye posMoa relative to the LED target center ft>r Subject 7 while gazmg 20* le ft ...... 280
22 Eye position relative to the r.RD target center for Subject 1 while gazing 30* le ft ...... 281
23 Eye position relative to the LED target center for Subject 2 while gazmg 30* le ft ...... 282
24 Eye position relative to the LED target center for Subject 3 while gazmg 30* le ft ...... 283
25 Eye position relative to the LED target center for Subject 4 while gazmg 30* le ft ...... 284
26 Eye position relative to the LED target center for Subject 5 while gazmg 30* le ft ...... 285
27 Eye position relative to the LED target center for Subject 6 while gazmg 30* left ...... 286
28 Eye position relative to the LED target center for Subject 7 while gazmg 30* le ft ...... 287
29 Eye position relative to the LED target center for Subject I while gazmg 40* le ft ...... 288
30 Eye position relative to the LED target center for Subject 2 while gazmg 40* le ft ...... 289
31 Eye position relative to the LED target center for Subject 3 while gazmg 40* le ft ...... 290
32 Eye position relative to the LED target center for Subject 4 while gazmg 40* le ft ...... 291
33 Eye position relative to the LED target center for Subject 5 while gazing 40* le ft ...... 292
34 Eye position relative to the LED target center for Subject 6 while gazing 40* le ft ...... 293
35 Eye position relative to the LED target center for Subject 7 while gazmg 40* left ------294
36 Eye position relative to the LED target center for Subject I while gazing 10* left with afterimage ...... 295
37 Eye position relative to the LED target center for Subject 2 while gazmg 10* left afterimage ...... 296
38 Eye position relative to the LED target center for Subject 3 while gazmg 10* left with afterimage ...... 2 9 7
39 Eye position relative to the LED target center for Subject 4 while gazing 10* left withafterima^ ...... 298
40 Eye position relative to the LED target center for Subject 5 while gazmg 10* left with afterim age...... 299
41 Eye position relative to the LED t a r ^ center for Subject 6 while gazmg W left with afterimage ...... 300
xxni 42 Eye position relative to the LED target center for Subject 7 while gazing 10* left with afterimage ...... 301
43 Eye position relative to the LED target center for Subject I while gazing 20* left with afterimage ...... 302
44 Eye position relative to the LED target center for Subject 2 while gazing 20* left with afterimage ...... 303
45 Eye position relative to the LED target center for Subject 3 while gazing 20* left with afterimage ...... 304
46 Eye position relative to the LED target center for Subject 4 while gazmg 20* left with afterimage ...... 305
47 Eye position relative to the LED target center for Subject 5 while gazing 20* left with afterimage ...... — 306
48 Eye position relative to the LED target center for Subject 6 while gazing 20* left with afterimage ...... 307
49 Eye position relative to the LED target center for Subject 7 while gazing 20* left with afterimage ...... 3 0 8
50 Eye position relative to the LED target center for Subject I while gazing 30* left with afterimage ...... 309
51 Eye position relative to the LED target center for Subject 2 while gazmg 30* left with afterimage ...... 310
52 Eye position relative to the LED target center for Subject 3 while gazmg 30* left with afterimage ...... 311
53 Eye position relative to the LED target center for Subject 4 while gazing 30* left with afterimage ...... 312
54 Eye position relative to the LED target center for Subject 5 while gazing 30* left with afterimage ...... 313
55 Eye position relative to the LED target center for Subject 6 while gazmg 30* left wAh afterimage ...... 314
56 Eye position relative to the LED target center for Subject 7 while gazmg 30* left with afterhnage ...... 315
57 Eye posMon relative to the LED target center for Subject 1 while gazmg 40* left with afterimage ...... 316
58 Eye position relative to the LED target center &r Subject 2 while gazing 40* left writh afterimage ...... 317
XXIV 59 Eye positioa relative to the LED target center for Subject 3 while gazmg 40“ left withafieriniage ...... 318
60 Eye positioa relative to the LED target center for Subject 4 while gazing 40“ left with afterimage ...... 319
61 Eye positioa relative to the LED target ceater for Subject 5 while gazing 40“ left with afterimage ...... 320
62 Eye positioa relative to the LED target ceater for Subject 6 while gazmg 40“ left with afterimage ...... 321
63 Eye positioa relative to the LED target center for Subject 7 while gazmg 40“ left afterimage ...... 322
XXV CHAPTER 1
INTRODUCTION
Ocular fixation is the act that brings the image of the object of regard into alignment with the fovea.* Subjectively, fixation may appear stable, but it is actually subject to continuous, dynamic errors. Studies have shown that during ocular fixation, the eye tends to drift randomly away firom the object of interest.^ Amplitudes of these drifts are typically less than 6 minutes of visual angle before miniature saccades (microsaccades) attempt to correct for this fixational error.’"’ In spite of these tiny eye movements, the mean fixational eye position relative to the target is exact during straight-ahead gaze.®"'® The standard deviation of straight-ahead fixation is also quite small (-2-7 minutes of visual angle).*"'® The characteristics of fixation have been examined in several studies, but most of these have been performed with the eye straight-ahead. Few have described ocular fixation at large eccentric angles of gaze (^30 degrees off straight-ahead). This research on extreme- gaze ocular fixation has concentrated on the alternating slow and fast movements of end-gaze nystagmus, and not necessarily on the microsaccades that also occur in extreme gaze." *’ Furthermore, little is known about the eye’s mean fixation position relative to the visual target (/.e., accuracy) or the standard deviation {Le., precision) of eccentric gaze. The accuracy of ocular fixation m eccentric gaze is of interest because a phenomenon analogous to the change in visual direction with vergence stress may also occur in extreme gaze. It has been shown that vergence stress, such as that evoked during attempted fusion of targets at large vergence angles, can lead to static vergence errors as large as I degree.'^ '* Errors of this magnitude are thought to cause dglopia, but did not do so in this experiment. It is believed that this vergence stress induced a change in visual direction^ which then permitted fusion even at these large vergence errors. In extreme gaze, the eye may be under conjugate stress as it attempts to maintain fixation- This may cause a perceptual adaptation in which the person believes the eye is rotated to a greater extent than it actually is. A different point on the retina would therefore come to represent the visual direction formerly represented by the fovea, a condition frequently called eccentric fixation. ‘ If eccentric fixation does occur at extreme angles of gaze, it might appear to researchers as a fixation lag. Indeed, Fogt and this author have obtained pilot data suggesting that while some subjects fixate accurately during eccentric gaze, many others tend to fall significantly short of the target.'® In addition, these fixation lags grow progressively through increasing angles of gaze. The pilot data mentioned above were likely confounded by an artifact in the eye position monitoring equipment. A scleral search coil was used in these studies to objectively measure and record the eye’s fixation position during extreme angles o f gaze. This technique is often selected because of its excellent resolution and exceptional lineari^ over a broad range of angles."’ ’*''* However, any significant search coil slippage occurring in extreme- gaze might have contaminated the pilot data. Apart from a pilot study by Fogt and the author”, no studies have specifically investigated this slippage issue, although several investigators have mentioned it as a possibility.'®’^ ^ Our pilot study measured scleral search coil slippage directly by means of high-magnification photography. Compared with straight-ahead, extreme-gaze horizontal eye rotations produced significant and progressively increasing search coil slippage. Furthermore, the direction of this slippage corresponded to the direction of “fixation lag” reported in the extreme-gaze pilot studies. While the presence of search coil slippage was confirmed, additional research was still required to determine whether it could have accounted for all of the fixation error measured in the mitial pilot studies. The investigation described in this dissertation has four main purposes. Fust, the accuracy and precision of ocular focation during extreme gaze will be quantified and analyzed using a scleral search cod. The amount o f slippage, if any, will also be assessed and its e& ct removed 6om the fixation data. If the resultant mean fixation position significantly lags that of the visual target, then conjugate stress-induced eccentric fixation will be indicated. If the resultant mean fixation position does not significantly lag that of the visual target, then accurate ocular during eccentric gaze is indicated. The presence of eccentric fixation will be confirmed by comparing the accuracy of extreme-gaze ocular fixation under two conditions; with and without a visual afterimage. A camera flash will create an afterimage that will surround (but not cover) the subjects’ fovea. The afterimage will then serve as aiming “cross hairs” to center the subject’s gaze accurately on a visual target. Assuming a compliant subject, this task will “force” the fovea on target and should eliminate eccentric fixation. The fixational eye positions under this condition will be compared with those measured without the foveal afterimage (which will allow for natural eccentric fixation). If natural fixation is eccentric, then the mean fixational positions of the two conditions should differ. Based on the pilot studies mentioned above, it is hypothesized that scleral search coil slippage will account for the majority of the “fixation error” occurring in eccentric gazes, and the remainder will be explained by conjugate stress-induced eccentric fixation. The second purpose of this dissertation is to investigate scleral search coil slippage. Dynamics of search coil slippage will be described, including the relationship between slippage amplitude and the angle of gaze, and whether the scleral lens consistently slips the same amoimt at a given angle. In addition, the direct method of Fogt and the author for detecting search coil slippage will be compared with the classic indirect method. Third, this research will examine the eye movements that occur during ocular fixation in extreme gaze, such as end-gaze nystagmus and microsaccades. Extreme-gaze eye movements will be compared with fixational eye movements that occur in straight-ahead gaze. Fourth, the feasibility of using subjects to calibrate the scleral search coil equipment will be investigated. For calibrating, search coil-based research has relied upon mechanical devices specifically designed for the task. These calibration devices typically consist of a search coil permanently mounted within a rotatable protractor. The device is rotated through an appropriate range of angles, and a calibration plot is produced of the equipment’s output signal as a function o f rotation angle, hi this study, the mechanical device calibration will be considered the gold standard with which to compare the subject calibration. A significant difference between the calibration slopes of the two sources would further confirm the presence of scleral search coil slippage and/or eccentric fixation. CHAPTER 2
HISTORICAL REVIEW
2.0 INTRODUCTION Little research has been directly related to the characteristics of ocular fixation in eccentric directions of gaze. Still, much literature has influenced the foundation, design and methods of this dissertation research. This literature and its relevance to the dissertation will be discussed in four main sections: (2.1) the direction of gaze, (2.2) foveal fixation, (2.3) objective methods to measure eye position and movements and (2.4) afterimages.
2.1 DIRECTION OF GAZE Three parameter values are required to specify where the eye is directed in space: (1) the ocular axis along which the eye’s gaze is directed, (2) the trajectory of the axis of gaze as the eye rotates and (3) the rotation of the axis o f gaze.
2.1.1 PRIMARY LINE OF SIGHT Multiple ocular axes can describe the eye’s direction of gaze. These include a group of closely-related axes that do not intersect the Avea, such as the pupillary and anatomical axes. Another ocular axis is the visual axis, which passes finrn the fixation target, through the nodal points ofthe eye, to the fiivea. However, the primary line of sight is considered the most appropriate axis to specify the eye’s direction o f gaze. This is the chief ray of the eye: it passes 6om the fîxadon target to the center of the entrance pupil, and then &om the center of the exit pupil to the fovea. The primary line of sight is the axis of choice, especially in the research setting, for two main reasons. First, the line of sight provides information on the location of both the fovea and the fixation target, whereas several other axes do not. Second, the position of the primary line of sight is relatively easy to determine. For example. Fry and Hill measured the primary line of sight position using only a moveable pinhole, a bite bar and a target.” A pinhole was placed in front of the eye to act as the eye’s entrance pupil, and the subject adjusted its position until a fixation target viewed through the pinhole was centered within its aperture. The subject’s primary line of sight coincided with the line through the centers of the target and the pinhole. In this dissertation project, the eye’s direction of gaze was monitored during fixation through various static eye rotations including straight ahead. Since understanding how the primary line of sight moves during eye rotations was important, it is presented next.
2.1,2 EYE CENTER OF ROTATION It was not known until 1963 whether the globe and primary line of sight pivoted about a single center of rotation or whether the behavior of the globe was more complex. The smooth, coordinated movements of the globe has suggested to some investigators that the eye behaves like a ball-in-socket. If it does, the eye would have a unique center of rotation, a point that during ocular rotation would have zero veloci^ both within the eye and within the orbit.** Fry and Hill ended the controversy. They located the center of ocular rotation by mapping the eye’s primary line of sight through a wide range of eye rotations.” While the plotted lines of sight did not cross at a single point, they did form a caustic {i.e., a semicircle). The center of cmvature for this caustic was determined to be the eye’s center of rotation. Figure 2.1 provides a schematic representing this principle. During horizontal rotations, the center of rotation of the eye is a single point 14.8 millimeters behind the comeal pole and 0.79 millimeters nasal to the line of sight.” It should be noted that some subjects (3 of the 31 they tested) feiled to produce a true center of rotation. The notion of a center of rotation may be an approximation, at least for some subjects.^-^* However, this subtlety is ignored in the present dissertation, and the primary line of sight is assumed to pivot with the globe about a concurrent center of rotation.
2.1 J POSITIONS OF GAZE As the eye and primary line of sight rotate about the center of rotation, there are three possible positions of gaze: primary, secondary and tertiary. Primary gaze is the “straight ahead position” of the eye (relative to the head). This is the eye position from which vertical or lateral fixational movements may be made without concomitant ocular torsion. ‘ Secondary gaze is any position of the eye represented by a vertical or horizontal deviation of the line of sight from the primary position.' Tertiary gaze is any oblique position of the eye. This eye position is represented by a combination of vertical ant/horizontal deviations of the line of sight from the primary position.' Tertiary gaze always incorporates concomitant ocular torsion. The experiments described in this dissertation used only primary and secondary positions of gaze. Subjects fixated a target while in straight-ahead gaze and at various lateral angles of eye rotation. Excluding eye rotations into tertiary positions simplified the experiment; rotations into tertiary positions would have required adoption of a special coordinate system {e.g.. Pick or Helmholtz) to describe the direction of gaze properly.^*^" In these experiments, the subject’s direction of gaze was specified with simple angles relative to the eye’s center of rotation. For example, the description, a “40“ eye rotation,” indicates that the eye rotated 40“ horizontally, away from straight-ahead, about its center of rotation.
2.2 FOVEAL FIXATION Foveal fixation is defined as normal fixation in which the hnage of the object of regard M is upon the fovea.' This section provides a general overview of various topics in foveal fîxation, including normal micro-eye movements, abnormal fixation, the neural integrator theory and the accuracy and precision of fixation.
2.2.1 MINIATURE EYE MOVEMENTS DURING FIXATION Subjectively, foveal fixation may appear stable, but it is actually subject to continuous, dynamic movements. Three categories of miniature eye movements occur during normal fixation: tremors, drifts and microsaccades. These “micro” eye movements are typically smaller than the diameter of the foveola, which subtends a visual angle of about 54 minutes of arc.^‘ These small eye movements do not degrade vision, and may actually improve it.^ “High-fiequency tremors” are ocular oscillations at 30-100 Hz with a relatively small amplitude (between 5 and 50 seconds of arc).^-^ “Slow drifts” are at ocular velocities of <15 minutes of arc/second and have amplitudes of <6 minutes of arc.^ Microsaccades have amplitudes ranging between 1-25 minutes of arc and occur 1-3 times per second.^^^ Of the three, only microsaccades are synchronous between the two eyes.’ Research with stabilized retinal images has suggested that tremor and drift are due to oculomotor intrinsic neural noise, which is thought to induce fluctuations in extraocular muscle fiber discharges.^ While tremors are typically too small to affect fixation, slow drifts often producing errors by moving the eye away firom the object of regard.^ Microsaccades correct this fixational error approximately.^-^ In addition, some researchers suggest that microsaccades provide the movement necessary to inhibit the Troxler phenomenon, the disappearance of a perfectly st^dy fixated object'-^ While this may be true under stabilized head conditions, it is thought that natural head movements contribute enough movement under normal conditions to stimulate vision during &ration. Furthermore, microsaccades are often suppressed during high visual acuity tasks.^“ The usefulness of microsaccades for vision is therefore a matto: of some debate. Microsaccades are thought to be involuntary, small-amplitude variations o f saccadic eye movements. Saccades are the abrupt, voluntary shifts in fixation fiom one point to another, such as those that occur in reading.^ The qre movement literature commonly
S presents saccade data as “main sequence diagrams.” These are plots of eye movement duration, peak velocity or peak acceleration, shown as a function of eye movement magnitude (i.e., amplitude). Main sequence diagrams show these parameters so clearly and conveniently that they are often used to identify saccades from otherwise unknown eye movements. Figure 22 shows a saccadic main sequence plot from Zuber and Stark.” It is obvious in this figure that the peak velocity of a saccadic eye movements increase in a non linear manner with amplitude.” "^^ Zuber and Stark found that the main sequence of microsaccades fell upon a curve that was continuous with the main sequence of the larger saccades.” This is illustrated in Figure 2.3. This led the authors to hypothesize that the microsaccades and the larger saccades “are produced by the same physiological system” within the central nervous system. Accordingly, a main sequence plot of the microsaccadic eye movements monitored in this dissertation will be created and compared to the saccade and microsaccade data of Zuber and Stark. While tremors, drifts and microsaccades are naturally associated with human fixation, “abnormal” eye movements can also occur. Since they, too, could appear in the data from this experiment, they are briefly described.
2.2.2 ABNORMAL FIXATION According to Citiffireda, there are three catagories of abnormal fixation: (1) slow drifts, (2) saccadic intrusions and (3) nystagmus.® Abnormal “slow drifts” typically occur in patients with amblyopia, and are centered aroimd a fixation point eccentric to the fovea.® These drifts are different fix>m the normal drift micro-eye movements, in that they are larger (amplitudes of < 1 degree compared to <6 minutes of arc), they are faster (velocities of ^3 degrees/second compared to 0.25 degrees/second) and they occur more irregularly.® Abnormal “intrusive saccades” include square-wave jerks, macro square-wave Jerks and macrosaccadic oscillations. All three types interfere with the foveal fixation of a target, and range in amplitude from 0.5 to 50 degrees.®’**®^® Square-wave jerks typically have amplitudes between 0.5 and 3 degrees and occur, at most, twice per second.® **^^ This intrusive saccade ‘^erkÿ’ the eye away from a fixation target. Then, following a 200 millisecond latency period, a second saccade takes the eye back to the target.*-'*^* '*^ Unlike the other two types of saccadic intrusions, square-wave jerks do not always indicate abnormal fixation, as they are also seen in 25% to 60% of normal patients.'*® Macro square-wave jerks are usually larger in amplitude than ordinary square-wave jerks. Their amplitudes are typically 20-50 degrees VA., and their fiequency of occurrence is approximately 2-3 Hz.'*^'*®*’*^ This type of intrusive saccade 'jerks" the eye away fix)m a fixation target via a saccade. Following a short latency period (80 milliseconds), a saccade returns the eye back to the target.^® Macrosaccadic oscillations have large amplitudes (up to 50 degrees), but otherwise resemble macro square-wave jerks.'*^’'*® '*^ Nystagmus is a regularly repetitive, typically involuntary, movement of the eye. The waveform of nystagmus may be either pendular (velocity is the same in both directions), or jerky (velocity is faster in one direction).' Pendular nystagmus has amplitudes between 0.5 and 10 degrees, a fiequency between 2 and 8 Hz and a peak velocity of sIOO degrees/second.® Jerk nystagmus is composed o f a slow phase (drift) away from the fixation target, followed by a fast phase (corrective saccade) back to the target. Jerk nystagmus typically has amplitudes between 0.25 and 5 degrees, a firequency between 1 and 5 Hz and peak velocities o f s 100 degrees/second.® Both pendular and jerk nystagmus attempt to briefly fbveate the target.®
2 2 3 FIXATION AND THE NEURAL INTEGRATOR Of course ocular fixation is not limited to the primary position of gaze. Therefore, many have investigated the neurological sequences required to initiate eye rotations toward an eccentric target and to maintain correct positioning of the eyes on target This dissertation research monitored the characteristics of fixation while the eye was positioned in both primary and secondary gazes. The maintenance of eye position during fixation in eccentric gaze was especially important in this regard. If the neurological control responsible for ocular fixation is inexact so, too, wül be the quality of fixation. When the eye rotates fiom primary gaze to obtain fr)veal fixation of an eccentric target rotation is initiated when the extraocular muscles (EOMs) receive commands
1 0 speci^ông eye-velocity.'*® This enables the EONfe to overcome the viscous and elastic forces of orbital tissue and to rotate the eye into the appropriate position. In saccadic eye movements, this velocity command is termed the “pulse.” Once the eye has reached the eccentric position, tonic contraction of the appropriate EOMs is required to maintain fixation. This tonic command, termed the “step,” specifies eye-position and is required so the muscles can counterbalance elastic restoring forces that tend to pull the eye back toward center.*” Research on premotor neurons has shown that only eye-velocity information is transferred out firom the brain stem toward the EOMs for primary conjugate motor commands saccades, pursuits and vestibular-ocular reflexes).” This is intriguing, since EOM motor neurons receive both eye-velocity and eye-position commands.*' These facts lead to the velocity-to-position neural integrator theory. The neural integrator is a mechanism located between the premotor and motor neurons, which mathematically integrates eye- velocity commands (originating in the brain stem) into the eye-position commands that are responsible for holding the eyes in eccentric gaze. Neural integrators are known to exist in other eye movement pathways. For example, in addition to the conjugate, there is also a vergence neural integrator and a widely-studied acceleration-to-velocity integrator specific to the vestibular-ocular system. An ideal velocity-to-position neural integrator would transform eye-velocity commands into appropriate and non-decaying eye-position commands. But even in normal subjects it has been shown that this neural integrator is actually physiologically “leaky,” causing the eye-position command to decay exponentially with time.*^ The time constant of decay for normal subjects viewing eccentrically in dark envhonments is approximately 20 to 70 seconds.*'’ A longer time constant indicates a less-leaky neural integrator, and therefore the eyes stray more slowly firom eccentric gaze (as compared to those subjects with shorter time constants). The neural integrator for horizontal conjugate eye movements is thought to be located in the medial vestibular nucleus and the nucleus prepositus hypoglossi.*'’’” The cerebellar flocculus and paraflocculus seem to improve the fidelity o f this inherently imperfoct brain stem neural integrator.^ The cerebellum works through a positive feedback mechanism to
II adjust the integrator’s time constant of decay. The cerebellum may increase the time constant to reduce drift of the eyes toward primary gaze. This would be done so as not to induce a deviation away from primary gaze and past the original eccentric fixation position. One type of nystagmus that was likely to be encountered in the current experiment was end-gaze nystagmus. End-gaze nystagmus consists ofjerlty eye movements that occur in normal subjects during eccentric (usually >30®) gaze either spontaneously or secondary to fatigue.E nd-gaze nystagmus is thought due to the velocity-to-position neural integrator. As a subject fixates eccentrically, this “leaky” neural integrator causes the eye- position command to gradually reduce. Concurrently, the eye begins to drift back toward primary gaze. This slow eye deviation (the slow phase o f nystagmus) stimulates corrective saccades in the opposite direction (the fast phase of nystagmus). Next, an overview is presented of the few studies that have actually measured the accuracy and precision of fixation in extreme horizontal gazes.
2.2.4 THE ACCURACY AND PREaSION OF FIXATION IN EXTREME GAZE While much research has dealt with ocular fixation, the majority has been restricted to the primary position of gaze. Investigations have shown that under stabilized head conditions, human monocular fixation in primary gaze is accurate {Le., with mean fixational positions centered over the visual target) and typically produces low standard deviations {i.e., high precision) around 2-7 minutes of arc.*‘‘“ Prior to pilot studies performed by Fogt and the author, only two publications have examined the accuracy of fixation in lateral gazes. While studying the stability of gaze during dynamic head rotations, Ferman et ai also collected data detailing the effects of static head deviations on gaze accuracy.^ A single, fixed target was located straight-ahead of the eye when the head was straight. Under monocular conditions, subjects fixated the target during static lateral head rotations of ±15®. For example, during a head rotation of 15®, the eye was required to rotate back 15® in order to frcate the target. The eye’s position was monitored with scleral search coil equipment (to be described in section 232) similar to that used m this dissertation’s research.
1 2 Ferman hypothesized that a linear regression of static gaze position on static head position would produce a slope of zero. If true, this would indicate accurate eye fixation during the full range of head rotations. Four of the eight subjects did produce slopes of approximately zero. However, the remaining four subjects produced slopes of over +0.01. Two of these slopes were +0.022 and +0.028, meaning that the subjects’ eyes fell short (i.e., undershot or lagged) the target by 20 and 25 minutes of arc, respectively, during 15“ head rotations. These translate into accuracies (/.«., [true eye rotation / eye rotation demand] x 100%) of 97.8 and 97.2%, respectively. Standard deviations were not listed for the eye position data collected during eccentric gaze. The overall standard deviation of straight-ahead fixation was 6.9 minutes of arc for the sample. Investigating the effects of static head rotations on gaze accurate was not the goal of Ferman’s research, so it was only briefly addressed. But clearly some subjects fixated accurately during eccentric gaze, while others tended to fall short of the target. An abbreviated article by Crone investigated the accuracy of fixation during various lateral gazes.“ A portion of the experiment used afterimage techniques to monitor the eye’s position while fixating a target during static eye rotations over ±40“. Results for the single subject indicated near-perfect target fixation during eye rotations of < 20“ During extreme excursions (^30“) however, a “slight lag” of fixation was noted. Maximum lags occurred during 40“ eye rotations but were only about 6 minutes of arc in size. The preceding two articles shed some light on the accuracy of fixation in eccentric lateral gazes, however neither utilized a statistical analysis, and the Crone results were based on only one subject. Fogt and the author have performed two pilot studies'^ to confirm Ferman’s accuracy results, and also to investigate how extreme lateral gazes affect fixation precision. In our studies, the subject’s head was held in place by means of a bite bar, contained the subjects in a sparse visual environment and utilized scleral search coil equipment similar to that of Ferman et al^ While monitoring three subjects, the first pilot study produced ^ ic a l fixation standard deviations (~ 7 minutes of arc) in straight-ahead gaze. In extrone gazes, only one
B of the three subjects showed substantially higher standard deviations (II minutes of arc). Overall, the three subjects were inaccurate in eccentric gaze, with progressively larger undershootings of the target with 20°, 30° and 40° eye rotations, respectively. In gazes greater than 30°, fixation lagged the target by 30 to 90 minutes o f arc. End-gaze nystagmus was produced in two subjects while fixating with a 40° eye rotation. This may have been due to the study’s long recording periods (30 seconds). The second pilot study measured fixation accuracy and precision during 20° and 40° eye rotations for two subjects. In straight-ahead gaze, the average standard deviation (Le., precision) o f gaze was 7 minutes of arc. Figure 2.4 plots the data collected for both subjects while in straight-ahead gaze. During a 20° eye rotation. Subject 1 overshot the target by 7 minutes of arc. Precision was ±6 minutes of arc. Subject 2 undershot by 12 minutes of arc, with precision of ±5 minutes of arc. Figure 2.5 shows the fixation data collected for both subjects during a 20° eye rotation. At a fixation position o f 40°, Subject 1 overshot the target by 8 minutes of arc. Precision was ±5 minutes of arc. Subject 2 imdershot the target by 32 minutes of arc, with precision of ±4 minutes of arc. Figure 2.6 shows the fixation data collected for both subjects during a 20° eye rotation. End-gaze nystagmus was absent in all cases, and all recording periods were 2 seconds. It should be noted that the data of the second pilot study contained significant intrinsic noise firom the scleral search coil equipment. The noise was at such a low firequency that attempts to filter it also removed critical low-firequency eye position data. Because of this, the intrinsic noise was not filtered. In this situation, the noise is expected to have a much larger effect on the standard deviation of the data than the mean eye position. The goals of this pilot study were to (I) measure the mean eye position while the eye fixated a target in extreme gaze, and (2) investigate how extreme lateral gazes affect fixation precision (i.e., does the precision of fixation change over different eye rotations). It was not as important at the time to measure the absolute precision of gaze. These study goals were reached even with significant intrinsic noise in the data. Collectively the two pilot studies suggest that at high eccentricity (r.e., 40°), fixation in subjects may be highly accurate (within 10 minutes of arc) while in others, fixation can
14 be inaccurate and lag the target by as much as 90 minutes of arc. This agrees with the work of Ferman et al.’ Precision in extreme gaze appears to be about the same as that in straight ahead gaze. Potential sources of error included the small number of subjects ancL most importantly, search coil slippage (to be described and discussed in section 2.3.3). The literature and pilot studies were valuable in creating a solid foundation for the dissertation research, however they produced another question. With the results of Ferman and the pilot studies, it was unclear whether subjects fixated inaccurately, or whether search coil slippage provided some (or all) of the observed inaccuracy. Answering this would require additional research including a larger subject pool and the use of both eye and search coil position monitoring devices. Monitoring the position of the eye can be accomplished by a number of different recording devices. Next, the two types of recording devices used in the dissertation research will be discussed, as well as the question of scleral search coil slippage.
23 OBJECTIVE MEASUREMENTS OF EYE POSITION AND MOVEMENTS Both the position of the eye and its movements can be monitored through a number of different recording devices. Table 2.1 lists common objective methods to assess eye position and movements, and lists the Qpical maximum resolution and linear tracking range for each device. Maximum resolution can be defined as the smallest eye movement measurable by the apparatus. The linear tracking range of the equipment is the range o f eye movements that, when plotted against monfeoring device output, produces a simple linear regression line with a correlation coefficient and slope of approximately 1.0. The first goal of this dissertation research was to investigate characteristics of extreme-gaze fixation. This demands that the eye position monitoring device have both excellent resolution and a large linear range. A resolution of approximately 3 minutes o f arc and a linear range of > 40° was requned. While purkinje image tracking, infiared limbal tracking, and electro-oculography are popular eye position monitors, their maximum resolution and/or linear tracking ranges are inappropriate for this experiment (Table 2.1).
15 With a resolution of < 1 minute of arc and potential linear range of ±I 80“, only the scleral search coil fit the necessary requirements. Figure 2.7 illustrates the linear tracking range of the scleral search coil equipment used in this experiment. While the scleral search coil was to be used in the experiment, there was still the question o f search coil slippage. Another goal of this dissertation research was to investigate this potential scleral search coil slippage on the eye. This was accomplished by directly photographing the search coil’s position while the eye fixated a target in various angles of gaze. This technique was identical to photography methods of monitoring eye movements (to be described in section 2.3.1). Photography and scleral search coil methods for objectively monitoring eye position will be described next.
2 J.1 PHOTOGRAPHY AND VIDEO Photography is a well-established technique used to measure eye position and movements by observing the motion of ocular landmarks or ocular reflections. The position of an ocular object is monitored over time.^ If the position changes between photographs, then the object (and the eye) has rotated. Figure 2.8 demonstrates this concept. To calculate the amplitude of an eye rotation based on the movement of an ocular landmark, two details must be known: (1) the linear distance, y, that an object has moved on the photograph and, (2) the distance, r, between the object and the eye’s center of rotation. The following equation is utilized:
y = r sin (©), Equation 2.1 where e is the angle of eye rotation. For example, an object on the comeal pole has moved horizontally on a photograph 0.5 millimeters. According to Fry and HilP, the distance between the object and the eye’s center of rotation is approximately 14.8 millimeters (±0.8). Therefore, y = 0.5 millimeters and r = 14.8 millimeters; e is calculated to be [arcsin(0.5/14.8)1, or 1.9“ (±0.I“). This example is illustrated in Figure 2.9.
1 6 Photographie methods are non-invasive and their resolution and noise are directly related to the quali^ of the camera. Disadvantages include a limited linear tracking range, the fact that subjects must be fixed immobile with a bite-bar and forehead rest (or the subject must wear a head-mounted video camera) and the diffîculty in diSerentiating between rotation and translation of the eye.
23.2 SCLERAL SEARCH COIL The scleral search coil method for recording eye positions and movements was first introduced in 1963 by Robinson.^ It has developed into a precise eye movement monitor with maximum resolution of < 1 minute of arc, low noise and a large linear range. All three dimensions of eye rotations (/.e., horizontal, vertical and torsional) can be monitored concurrently with this equipment, and it is relatively unaffected by translational head movements.**’^'^* A subject wears a scleral search coil, an annular silicone contact lens in which multiple coils of copper are imbedded. Figure 2.10 illustrates a subject wearing a scleral search coil. The subject is placed near the center of a large (e.g., 1 meter^) cube-shaped structure (Figure 2.11), where horizontal and vertical oscillating electromagnetic fields are imposed by Helmholtz field coils attached inside. When the scleral search coil is subjected to this fluctuating magnetic field, a voltage is induced in the coil.^-^® This voltage progressively changes in proportion to the sine of the angle between the search coil and the magnetic field.” -® The primary disadvantages of the scleral search coil technique are due to the contact lens: topical anesthetic is required before inserting the lens, and there is mild discomfort for the subjects while it is being worn. In addition, controversy exists about whether the search coil slips during eye rotations.
233 SCLERAL SEARCH COIL SLIPPAGE Although no studies have specifically investigated this potential slippage of the modem scleral search coil, several researchers have mentioned the possibility.*^-^*’’^ Hence,
17 one strategy is commonly used during scleral search coil studies to assess stabili^ of the scleral lens on the eye. This is an indirect method popularized by CoUewijn et ai, where variability in the recordings describing the eye’s position is monitored.** It is assumed that search coil slippage would be revealed by inconsistencies between data describing a subject’s fixation in primary gaze before and after large saccadic eye movements.’-**^‘ “ For example, Coilewijn et al. monitored subjects’ fixation eye positions in straight-ahead gaze before and after a 20° horizontal saccade was performed.** Since no significant difference was found between the two data sets, the authors concluded that the scleral lens was firmly adhered to the globe. A key assumption underlying this method is that if the search coil does slip relative to the eye, it will stabilize at its new position. The method will fail to detect search coil slippage if the lens slips during an eye movement into eccentric gaze, but then returns to its original position as the eye returns to primary gaze. Overall, this technique has never shown evidence for significant search coil slippage in any study.’•** *‘ “ A single study has shown experimental evidence of search coil slippage. While studying the instability of ocular torsion during fixation. Van Rijn et ai produced data suggesting search coil slippage over the long-term. This was possibly induced by vigorous inter-trial blinking.'® From their data, the authors inferred that: (1) the coil may rotate relative to the bulbar conjunctiva, and/or (2) the bulbar conjunctiva may concurrently rotate with the coil, with both returning to their original position because of elastic restoring forces. The consequences of search coil slippage are important. If the scleral lens does slip while the eye is positioned into eccentric gaze, then any study that has used search coils in extreme gaze may have produced artifactual data. To investigate this question, Fogt and the author performed a search coil slippage pilot study on ten human subjects.’’ High- magnification photography techniques (identical to those used in the dissertation research) were used to monitor directly the position of the scleral search coil on the globe. As compared to primary gaze, both 30° and 40° nasal eye rotations produced statistically significant search coil slippage (182 and 31.4 minutes of arc, respectively). The standard deviations of search coil position also increased with eccentricity, suggesting instability of the coil. During nasal qre rotations, the cod consistently slipped temporally, possibly because
18 of contact between the coil and the palpebral conjunctiva. In addition, the direction of this search coil slipp^e corresponded to the direction of fixation lag found in extreme-gaze accuracy research (section 22.3). Figure 2.12 illustrates the results of the study. Much like the extreme-gaze accuracy and precision pilot studies (section 22.3), this slippage pilot study was valuable in creating a solid foundation for the dissertation research. Most significant, it demonstrated that search coil slippage can occur during extreme horizontal eye rotations, and that this lens slippage could potentially masquerade as fixation lags during extreme-gaze experiments. Accordingly, this dissertation research will address whether subjects fixate inaccurately in extreme-gaze or whether search coil slippage provides some (or ail) o f the error. The dynamics of search coil slippage will also be investigated, such as whether the scleral lens consistently slips the same amount at a given angle. And, the direct high-magnification photography method of measuring search coil slippage will be compared with the classic indirect method of Coilewijn^*. Specifically, Collewijn’s assumption that if the search coil slips on the eye, it will stabilize at its new position will be questioned. Besides the scleral search coil and photography equipment, another tool, the afterimage, was used in the dissertation to investigate the characteristics of extreme-gaze fixation.
2.4 AFTERIMAGES An afterimage is a persisting sensation or image perceived after the correlated physical stimulus has been removed.' ® Afterimage techniques have been used widely in research and clinical communities to measure eye position and movements subjectively^*’®*^*, to evaluate retinal correspondence*^^ and to mvestigate saccadic suppression^, stereoscopic localization^ and the precision of eye movement monitors'^. All afterimage-based methods rely on the fact that an afterhnage provides a retmal ‘^landmark” that is visible to the subject. Displacements of an afterim^e in the visual scene dhectly reflect shifts in the direction of
19 the visual axis of the eye.’*^ In other words, afterimages are considered to be completely stabilized retinal images which move with the eyes into different gazes It is not known whether the eye's fixation pattern changes while in extreme angles of gaze. The fixation lag result found by Ferman’ and the two pilots studies'^ (section 2.2.3) suggests that some subjects may resort to eccentric fixation when viewing targets in extreme gaze. The eye would cease employing the central fovea during these situations, possibly because of conjugate stress. Afterimage techniques were used in the dissertation research to investigate this potential eccentric fixation. A camera flash created an afterimage which surrounded (but did not include) the subjects’ fovea- The afterimage was then used by the subject as aiming “cross hairs” to center about an LED target during primary and secondary gazes. Assuming a compliant subject, this task “forced” the fovea on target and eliminated eccentric fixation. The results of this will be compared to those of the same situation but without the foveal afterimage (where eccentric fixation would be permitted to occur naturally). If eccentric fixation were present, then it would be noted in this comparison of afterimage/no afterimage conditions. Since the fovea was used during the afterimage condition, the search coil recordings obtained during this condition were taken to indicate the “no eccentric fixation” values. This will be discussed fiirther throughout the upcoming chapters. The idea that an afterimage can be used to monitor the direction of the eye has never been seriously challenged.’* However, it seems possible that at extreme angles of gaze, retmal stretching’’^' or crystalline lens displacement^ could affect the perceptual localization of the fovea and afterimage in visual space.” This theory will be termed “optical sliding.” If present, optical sliding would affect the dissertation research in two ways. The first example assumes that error due to search coil slippage (if any) has already been removed fiom the data. Here, objective data describmg the eye’s position with the use of an afterimage would reveal a displacement of the mean fixation position fix>m the visual target during extreme gaze. This fixation aror would be due to optical sliding. Errors found during fixation without the use o f an afterimage would be due to eccentric fixation and optical sliding. The comparison of the afterimage/no afterimage conditions would stül indicate
2 0 eccentric fixation, and the fixation inaccuracy foimd in the afterimage condition would indicate the error due to optical sliding. The second area to be afiected by optical sliding would be the comparison of scleral search coil calibration techniques. Compared to those of mechanical devices, calibrations performed by human subjects would contain error fiom two additional sources: optical sliding and search cod slippage. The error due to optical sliding could be foimd by correcting the human’s eye position data for scleral lens slippage.
2 1 t Purkinje image tracker < 0.5 degree ± 20“ Video/Photography-based systems < 0.5 degree ± 30“ Infiared limbal reflection techniques <1 arc-min (potential) ± 10“ Electro-oculography (EOG) 1 degree ± 30“ Magnetic scleral search coil <1 arc-min ± 180“ (potential)
TABLE 2,1: Objective methods to assess eye position, and their respective resolution and linear tracking ranges.'*’’^®
2 2 C austic
C e n te r o f R otation
FIGURE 2.1; During lateral eye rotations, the lines of sight (represented by straight lines) do not cross at a single point, rather they form a caustic within the eye. The center of curvature of the caustic corresponds to the center of rotation of the eye. According to Fry and Hill^, the center of rotation of the eye is a single point 14.8 millimeters behind the comeal pole, and the radius of curvature for the caustic is approximately 0.79 millimeters. Adapted from Fry and
23 1000
a « I I 100 • ft I g s 3 10 s 3 s
1 1 10 100 1000 AMPLITUDE (MINUTES OF ARC)
FIGURE 2.2: Main sequence plot of the saccade data of Zuber and Statk/^ The peak velocity of the saccade is shown as a nonlinearly increasing function of its amplitude.
24 1000
Q
IC /3 100 - it Is Û Ï
fid1 > 10 2 a.
1 1 10 100 1000
AMPLITUDE (MIN OF ARC)
FIGURE 23: Zuber and Stark's main sequence plot of microsaccades and saccades; 36 Triangles represent microsaccadic data, while the circles represent the saccade data presented in Figure 2.2. The peak velocity of the eye movement is shown as a function of its amplitude. An obvious connection exists between microsaccades and saccades, as the two data groups produce a continous curve.
25 g -10
TIME (SECONDS)
FIGURE 2.4; Eye position relative to the target center for Subject 1 and Subject 2 while gazing straight-ahead. This data collection occurred during four separate 2-second trials (represented by A, B, C and D, respectively). Negative position values indicate gaze undershoots. Sinusoid patterns in the data are due to intrinsic noise of the scleral search coil equipment, and could not be successfully removed without damaging true low-frequency information. < u. O z
z 0 E
1fid > tà
T im e (seconds )
FIGURE 2.5: Eye position relative to the target center for Subject I (top) and Subject 2 while fixating 20" left Negative position values indicate gaze undershoots. Sinusoid patterns in the data are due to intrinsic noise of the scleral search coil equipment^ and could not be successfully removed without damaging true low-jfiequency eye position infiiimation.
27 < 0 5 S I1 u > Ed
T im e (SECONDS)
FIGURE 2.6: Eye position relative to the target center for Subject I (top) and Subject 2 wbüe fixating 40** left Negative position values indicate gaze undershoots. Sinusoid patterns in the data are due to intrinsic noise of the scleral search coil equipment, and could not be successfully removed without damaging true iow-fiequency eye position information.
28 Is £ z 0 1 s X Ë u % Q tà X 3 co < Cd S
-10
-10 0 10 20 30 40
T r u e Se a r c h C o il Po s it io n (degrees )
FIGURE 2.7; The relationship of true eye position to measured eye position for the scleral search coil equipment utilized in this experiment. The linear regression equation is |y = (-3.4 * 10*^ + Ix], producing a correlation coefficent of 1.0 through this range o f eye rotation angles.
29 FIGURE 2.8: Photographie method to monitor eye rotations. (A), The eye in strai^t-ahead gaze. A large, black dot represents a fixed landmark oa the ocular surface. (B), The eye in right gaze. The black dot landmark has linearly displaced fiom its original position due to the eye's rotation. This distance, y, is shown as a solid horizontal line.
30 FIGURE 2.9: Example of a calciüatîoii of the amplitude of an eye rotation based on the movement of an ocular landmark. ^ the comeal pole rotates about the ocular center of rotation (COR) fiom position A to position B, the lateral displacement would equal the distance firom C to B. If the distance between COR and B is 14.8 millimeters, and the distance between C and B is 0.5 millimeters, then the angle o f ^ e rotation is [Asin(0.5/14.8)], or 1.9°.
31 FIGURE 2.10; The scleral search coil after msertioa onto the eye.
32 33 10 20 30 40
E y e R o t a t io n a n g l e (degrees )
FIGURE 2.12; The mean search coil slippage for each nasal (Le., leftward) eye rotation angle. Positive units indicate temporal (Le., rightward) slippage of the coil. Error bars= ± I standard deviation.
34 CHAPTERS
METHODS AND MATERIALS
3.0 INTRODUCTION The primaiy goal of this research was to determine the characteristics of ocular fixation in extreme gaze. In this chapter, two sets o f procedures are described that were used to reach this objective. First, a scleral search coil contact lens was fitted to the right eye of ten adult human subjects. Search coil equipment was used to objectively measure the eye's fixation position through multiple nasal gazes (i.e., 0°, 10®, 20®, 30® and 40®). However, in extreme angles o f gaze, search coil slippage could have contaminated this eye position data. Therefore the second procedure was to objectively measure the amount of search coil slippage occurring during eye rotations. This was accomplished by using a bigh- magnification photography technique.
3.1 SUBJECTS Ten young, adult, human subjects (6 female, 4 male; aged 22-28) were enrolled into this study. This sample size was based on the t-test utilizing an alpha of 0.05 (two-tailed), a power of 90%, an estimated effect size of 10 minutes of arc and an estimate of population fixation standard deviation of 7 minutes of arc.'^ Eight o f the ten subjects were Ohio State University College of Optometry studoits. The remaining two were the author and his wife. Only the right eye o f each subject was employed for the study.
35 Subjects were enrolled into the study based on the criteria listed in Table 3.1. Those enrolled were educated about the study procedures, risks and their right to withdraw fiom the study at any time. An informed consent form approved by The Ohio State University Health Sciences Human Subject Review Committee was read and voluntarily signed by each subject before study initiation. A copy of this informed consent form is provided in Appendix A. Each subject was given a thorough pre-study ocular examination. The first half of the exam included a subjective assessment. The subjects had no history of binocular or monocular vision anomalies, and no complaints of diplopia. This criterion was used to exclude subjects predisposed to fixation abnormalities, the most significant being eccentric fixation. There was no history of ocular disease, surgery or trauma to the right eye. The presence o f any of these could cause improper fit of the scleral search coil, hinder ocular fixation or degrade the optical quality of the eye. There were no medical conditions, medications or allergy conditions that contraindicated contact lens or scleral search cod wear. The second half of the pre-study ocular examination was an objective screening. Refinctive status of both eyes was evaluated to insure that the subjects were within protocol. Slit lamp biomicroscopy was performed on the anterior ocular segment, and the posterior segment was assessed through undilated pupils. Binocular vision status was evaluated objectively by the unilateral and alternating cover test, and subjectively by the Maddox rod test** Eccentric fixation was assessed by direct ophthalmoscope visuoscopy™, and stereopsis was measured using the Randot stereogram. To insure adequate uncorrected visual acuity during the experment all subjects were required to have a spherical equivalent refiactive error between ±1.00 D and less than 1.00 D of cylinder in the right eye. Calculated by vector length techniques*^, the average refiactive error in the right eye was -0.09 DS -0.15 DC x 096. Uncorrected distance visual acuity for the sample included 20/15 (6 subjects), 20/20 (2 subjects), 20/30± (I subject) and 20/40 (I subject). Both subjects with distance visual acuity worse than 20/20 had refiactive errors near -0.75 D. The far point for these subjects was therefore near the plane of the visual target used in the experiment AH subjects were correctable to 20/15 visual acuity in both the right and left eyes.
36 There was no ocular tissue inflammation, infection, degeneration, trauma or structural anomaly present that would hinder the study. Retinal correspondence was normal, there was no eccentric fixation present in either eye, and stereopsis was 20 seconds of arc in all subjects. Again, these conditions were assessed in an effort to exclude subjects predisposed to fixation abnormalities, hindered fit of the scleral search coil or poor ocular optical quality. While all ten subjects completed the study, irregular scleral search coil equipment noise during data collection required that data fiom three subjects be eliminated firom the analysis. The Results chapter will explain the rationale for this in detail. Removal of three subjects did not appear to effect the outcome of the study. Overall, the average refractive error in the right eye was altered only slightly, resulting to -0.02 DS -0.22 DC x 096. Table 3.2 provides the pre-study examination profile for the remaining seven subjects.
3.2 PHOTOGRAPHY EQUIPMENT SETUP PROCEDURES Search coil slippage at extreme angles of gaze was evaluated with identical equipment and methods as those of the slippage pilot study (section 2.3.3). The equipment consisted of a non-torsional scleral search coil contact lens (Skalar), and a modified slit lamp equipped with Digivid 2000 (Helioasis), a high-resolution digital ocular photography and storage system. Before arrival of a subject, all equipment was disinfected and the scleral search coil was prepared. The inside temporal edge of the search coil was marked with a black, non toxic permanent marker. This allowed for better edge resolution on photographs. It was then sterilized by soaking in 5% hydrogen peroxide solution and rinsed in sterile saline. A dental impression bite bar was used to stabilize the head relative to the modified slit lamp (Figure 3.1). The bite bar unit could rotate the subject’s head in the horizontal meridian (±40® relative to straight-ahead) about the approximate center of eye rotation. An adjustable forehead rest helped insure that the subject’s head was fiirther stabilized and erect It was not possible to guarantee that every subject’s ocular center of rotation was exactly coincident with the bite bar’s center of rotation. During fixation of an immobile target, if the center of eys rotation was not concurroit with the bite bar’s center of rotation.
37 photographie parallax arors would occur with rotations of the head. Figure 32 illustrates this concept. Parallax errors would cause inaccurate measurements of the search coil position relative to the eye; the search coü could actually appear to slip relative to the eye when it actually did not, or conversely, the search coil could appear stationary relative to the eye when it actually had slipped. To eliminate this parallax problem, a movable LED/pinhole target system was designed. Figure 3 .3 illustrates the principle behind this equipment An LED target which subtended a visual angle of 45 minutes was placed 13 centimeters ftom the subject’s center of eye rotation. The LED was fixed within and shown through a tube of 2 centimeters length. The LED was then visible through the pinhole. With this arrangement, exiting light was always parallel to the LED tube axis and to the slit lamp optic axis. For proper placement during the study, the LED/pinhole could be translated horizontally and vertically until the subject could see the LED target as round and centered within the pinhole. This LED/pinhole arrangement is analogous to viewing a small target through a drinking straw. The target is visible and centered in the tube only when the straw is along the ocular line of sight (/.e., the axis passing firom the target center to the center of the entrance pupil, and then firom the center of the exit pupil to the fovea). If a camera is now attached to the outside o f the straw and points toward the eye, then photographs taken of the external eye would be firom a fixed viewing angle. If the eye is translated, the position of the straw can be maneuvered and repositioned until the target is again visible and centered. Assuming that the camera remains a constant distance away firom the eye, photographs of the external eye will always be taken firom identical viewing angles. This method therefore eliminates photographic parallax errors even if the eye is translated during head rotations. The subject was fixed on the bite bar with the head facing straight-ahead (Figure 3.4). The left eye was patched, and the room lights were extinguished. The subject looked through the pinhole and adjusted the LED/pinhole unit laterally and vertically until the LED was round and centered within the pinhole. At this point, the subject’s line of sight was centered along the LED^inhole axis. To insure that the range of adjustment of the LED/pinhole unit would be adequate for the subject during the experiment, the investigator then rotated and
38 fixed the bite bar unit (and the subject) 40° to the right (Figure 3.5). The subject looked through the pinhole (/.e., by making a 40° nasal eye rotation) and adjusted the LED/pinhole unit laterally until the T.RD was again round and centered within the pinhole. These procedures were successful for all subjects.
33 SEARCH COH. EQIUPMENT SETUP PROCEDURES For each subject, scleral search coil equipment was utilized to measure the position of the eye objectively during fixation. Prior to data collection, the subject was acquainted with the bite bar unit and T-FD target. The equipment utilized within this portion of the study was identical to that of the second fixation pilot study (section 2.2 J). This consisted of a scleral search coil contact lens, a Helmholtz field coil cube (CNC Engineering), signal amplifiers, a Tektronix monitor, a 16-bit analog-to-digital data converter (ComputerBoards), a Pentium-based computer, a 16-bit digital-to-analog data converter and an arc perimeter containing LED targets. Figure 3.6 presents a flowchart diagram of this instrumentation. Setup began 35-40 minutes before the subject session. The equipment was turned on and allowed to stabilize for 30 minutes. The position bandwidth was 80 Hz - 2 db with 1 minute of arc peak-to-peak noise for a 30° eye movement** The phase was selected so that positive horizontal and vertical signals corresponded to right and upward eye movements, respectively. Calibration was performed prior to the subject’s arrival. This was conducted with a special search coil permanently fixed within a solid protractor unit (CNC Engineering) using a Visual Basic computer program. The program and form are listed in Appendix B, Program 1. The protractor was rotated to preselected horizontal angles (JLe., -10°, 0°, 10°, 20°, 30°, 40° and 50°) and to preselected vertical angles (r.e., -10°, 0° and 10°). At each angle, the computer recorded 1000 digital signals at a rate o f500 Hz. The calibration protractor unit was then removed fiom the Helmholtz field coil cube. Once all the calibration angles were recorded, a simple linear regression was produced for the plot o f digital signal versus sme of the angle o f rotation. The slope of this
39 regression line was used to calculate the magnitude of eye rotations for all subjects run during that particular day. Later, each subject's average zero position (f.e, both head and eye pointed straight-ahead) data was used as the y-intercept of the calibration linear regression. All calibration regression lines produced a correlation coefficient of 1.0. The calibration was performed with a solid protractor unit rather than with the human subject for several reasons. First, there was potential for sclaal search coil slippage relative to the subject's eye during the large eye rotations required during calibration. While the issue of search coil slippage is controversial, the question was eliminated by utilizing the protractor unit. Second, the use of the protractor unit prior to the subject's arrival allowed the investigator to quickly verify that the equipment electronics were functioning correctly. If an error was found, there was still time to correct the problem before inconveniencing the subject. Third, scleral search coil-based research has relied upon these mechanical devices specifically designed for calibrations.’’^°“ *^*^ Human calibrations are typically not performed. The subject was placed on a dental impression bite bar for stabilization within the Helmholtz field cube. Figure 3.7 illustrates the wooden bite bar unit. The bite bar had the ability to rotate the head in the horizontal meridian (e.g., for a head rotation of 40° right). It could also be used to adjust the subject in three-dimensions in order to place the subject's center of eye rotation concurrently at (1) the center of the Helmholtz field cube and (2) coincident with the bite bar's axis of horizontal rotation. 1 meter from the subject's center of eye rotation (well outside the Helmholtz field cube) was placed a 1-meter-radius arc perimeter with concave surface facing the subject Hence, the subject's center of eye rotation was at the center of curvature of the perimeter. LED targets were placed at 10° intervals along the arc perimeter radius, and were consequently named by their respective position on the arc perimeter (re., the 0° LED target was straight-ahead of the eye's center of rotation, the 10° LED target was 10° to the right of the 0° LED, ere.). Individual round targets were approximately 1.5 millimeters in diameter, and subtended a visual angle of 6 minutes at the 1 meter distance. The arc perimeter was black so that only the lighted LED was visible to the subject.
40 It should noted that this dissertation attempted to use visual targets of minimal size. This was based on the hypothesis that the eye may Sxate more accurately with smaller targets. Stehunan has shown statistical differences in the mean fixation position for targets of different size (ranging firjm 1.9 to 87.2 minutes of arc), luminance and color.** However, the largest observed discrepancy was only 3.9 minutes of arc, and under most conditions it was less than 2 minutes of arc. A pinhole (subtending approximately 10 minutes of arc) was temporarily attached to the Helmholtz field cube. This pinhole was 50 centimeters firom the subject and rested between the eye and the 0“ LED target The subject was fixed on the bite bar with head facing straight-ahead. The left eye was patched. The subject looked through the pinhole and adjusted his/her orientation laterally and vertically until the 0“ LED was visible. At this point the subject’s line of sight was centered along a line fi-om the center of the field coils to the LED. The investigator then rotated and fixed the bite bar unit (and the subject) to the right 40°. Once again, the subject looked through the pinhole and adjusted his/her fore/aft position until the 0° LED was visible. At this point, the subject was properly positioned for the study; the eye’s center of rotation was over the axis of horizontal rotation of the bite bar unit. To test this placement, the subject fixated the LED through the pinhole as the bite bar unit was rotated back to the original 0° position. For all subjects, the LED was continuously visible through the pinhole. Finally, the pinhole was removed from the Helmholtz field cube.
3.4 EXPERIMENTAL PROCEDURES Two sets of procedures were performed on all subjects: (1) photography equipment procedures to measure scleral search coil slippage and (2) scleral search coil equipment procedures to objectively measure the position of the eye during fixation. Before any procedures were performed, the scleral search coil was placed on the subject’s bulbar conjunctiva and was allowed to stabilize fi)r 7 minutes. The left eye remained patched, and the room lights were extinguished throughout the experiment
41 3.4.1 PHOTOGRAPHY EQUIPMENT PROCEDURES After being fixed on the bite bar and &rehead rest, the subject’s head was rotated and stabilized at angles of 0“, 10", 20°, 30° and 40° (in random order) about an axis passing through the estimated center of rotation of the subject’s eye. At each angle, the subject looked back at the LED target (therefore making a 0°, 10°, 20°, 30° or 40° nasal eye rotation, respectively). To insure that the comeal plane was perpendicular to the slit lamp axis, the movable LED/pinhole target position was adjusted until the LED target was visible and centered in the pinhole. At this point, the subject’s line of sight was directed along the appropriate axis and photographic parallax errors were eliminated Figures 3.4 and 3.5 illustrate (a) the bite bar position and (b) subject position at head rotations of 0° and 40°, respectively. While the subject fixated the LED target, the examiner photographed the inner search coil edge nearest the temporal limbus using the slit lamp and Digivid 2000. All head rotation angles were repeated three times in random order. A total of 15 photographs were taken (three at each gaze angle). The subject was removed from the apparatus. For calibration, an additional photograph was taken of a millimeter ruler at the focal point of the camera. This placed the ruler the same distance from the camera as the search coil edge photographed earlier. For each subject, the study photographs were viewed in random order by a single reader, the author, on a 17-inch computer monitor (800 x 600 pixel resolution) at a magnification of lOOx. The reader measured the linear horizontal distance between the most anterior portion of a pre-selected limbal conjunctival blood vessel and the scleral search coil edge. Limbal blood vessels were chosen because they were unlikely to move significantly with eye rotations. Distances as small as 0.01 millimeters could be measured. Search coil slippage occurred if a measurement was different from the average search coil position for the straight-ahead eye position. This procedure was a variation ofthe photography techniques used in measuring eye movements (section 23.1). Figure 3.8 illustrates slippage of the scleral search coil.
42 Slippage was calculated based oa the appioximation that the radius of curvature of the bulbar conjunctiva was approximately 11.8 millimeters. The equation used was a manipulation of Equation 2.1 (section 2.3.1):
e = arcsin (( y / m) /11.8) x 60, Equation 3.1 where y is the linear slippage (/.e., the difference in millimeters between a measured search coil position and the average straight-ahead search coil position), m is the size of the photographed millimeter and © is the search coil angular slippage (minutes of arc). The conjunctival radius of curvature approximation introduced the most potential error into the slippage calculation. Figure 3.9 shows slippage calculation errors plotted as a function of bulbar conjunctiva radius of curvature. For example, by assuming an 11.8 millimeter conjunctival radius of curvature, this dissertation underestimated search coil slippage by approximately 8% for a subject with a 10.8 mm conjunctival radius of curvature. To the knowledge o f this author, no data is available which describes the human bulbar conjunctiva radius o f curvature. An educated guess on the normal range of diameters for the external globe (cornea excluded) might be 212 to 26.0 mm. This range corresponds to errors in search coil slippage calculations of 10% or less. Considering the size of scleral lens slippages measured in the pilot study, this amount of potential error is modest.
3.4.2 SEARCH COIL EQUIPMENT PROCEDURES The search coü equipment procedures were performed using a Visual Basic computer program. The form and code of the program are shown in Program 2 of Appendix B. Two experimenters were used for this portion o f the experiment One experimenter operated the computer whüe the other rotated the subject’s head and controUed application of the afterimage. Subjects were tested monocularly; the left eye was occluded throughout the study sœsion. The testing environment was visually “sparse.” The room windows were covered, and the three walls adjacent to the Helmholtz field cube were painted black. FinaUy, a thick
43 layer of black felt was placed between the subject and the computer operator, and the room lights were extinguished during the session. The procedures were run in the following order. 1. Head positioned straight-ahead.The subject was placed within the Helmholtz field cube on a wooden chair, and was fixed on the bite bar with the head and eye facing straight-ahead. The scleral search coil leads were connected to the recording equipment Individual LED’s were then illuminated in the following angle sequence: 0“, 10°, 0°, 20°, 0°, 30°, 0°, 40° and OP, Figure 3.10 provides a schematic representing this situation. For each LED target when the subject felt confident that (s)he was viewing the target (s)he pressed a computer mouse button. At that time, 1000 eye position signals were digitized over 2 seconds by the 16-bit A/D converter at a rate of 500 Hz. 2. Head positioned at four different angles {without an afterimage). The next series of data collection required the subject’s head to be rotated and stabilized to the right 10°, 20°, 30° and 40° about an axis passing through the center of rotation o f the subject’s right eye. The angle procession followed the sequence used during the “photography procedures,” except that the third measurements at each head angle {Le,, 10°, 20°, 30° and 40°) and all straight-ahead positions were eliminated. The LED targets were the same as those used in the previous section. Figure 3.11 provides a schematic representation of this portion of the experiment While the subject remained fixed on the bite bar, the researcher rotated and stabilized the bite bar (and therefore the head) to the right at the predetermined angle. The LED directly ahead of the subject {e,g,, the 30° LED for a 30° head rotation) was illuminated. When the subject felt confident that (s)he was viewing the target, (s)he pressed a computer mouse buttoiL At this time, the computer recorded 1000 digital signals at a rate o f500 Hz. Next, the 0° LED was illuminated. When the subject felt confident that (s)he was viewing the target, (s)he pressed a computer mouse button. At this time, the computer again recorded 1000 digital signals at a rate of 500 Hz. This procedure was repeated until data were randomly collected twice for each head rotation angle, giving a total of eight sets o f data. 3. Head positioned at four different angles {with an afterimage). As in the experiment described m the previous section, the next series of measurements required the
44 bite bar to be rotated and stabilized to the right 10°, 20°, 30° and 40° about an axis passing through the center of rotation of the subject's right eye. hi addition, a pinhole was placed between the subject and the 0° LED, and an afterimage was flashed in hront of the right eye. The angle sequence exactly matched the sequence utilized in the previous experiment, and it used the same LED targets. Figure 3.12 provides a schematic representation of this experiment While the subject remained fixed on the bite bar, the researcher rotated and stabilized the bite bar to the 0° position (/.e., the subject’s head faced straight-ahead), and attached the pinhole to the Helmholtz field cube. This is the identical pinhole described and used in the search coil equipment setup procedures listed in section 3.2. A camera flash unit (Promatic FT1700) was placed 50 centimeters firom the subject’s eye. On the flash unit was placed an LED target centered on the flash glass (for patient fixation). Surrounding the LED target was a “plus-sign” template. As the subject fixated the flash’s LED target, the investigator flashed the light, leaving a plus-sign-shaped afterimage surroimding (but not including) the subject’s fovea. A schematic of this afterimage is shown in Figure 3.13. The approximate outside diameter of the afterimage was 2° (visual angle), with arm thicknesses of 15 minutes of arc, and a center (foveal) opening of 20 minutes of arc. For each measurement, the subject was instructed to center the plus-sign afterimage over the LED targets, hereby positioning the fovea directly over the target. While the subject remained fixed on the bite bar, the researcher rotated and stabilized the bite bar to the right at the predetermined angle. After the 0° LED was illuminated, it was visible through the pinhole. Assuming a compliant subject, the afterimage “forced” the fovea on target and eliminated eccentric fixatioiL The 1 ED target, pinhole and fovea provided the exact line of sight for the eye. When the subject felt confident that (s)he was centering the plus-sign afterimage over the target, (s)he pressed a computer mouse buttoiL At this time, the computer recorded 1000 digital signals at a rate o f500 Hz. This was repeated randomly twice for each angle, for a total of eight sets o f data. The afterimage remained visible to the subject durmg most o f this data collection. Once it disappeared, the afterimage was reapplied using the procedures listed above. TypicaUy this occurred once during a sessioiL
45 3.5 DATA OVERVIEW For the goal of determining the characteristics of ocular fixation in extreme-gaze, only data collected whüe the subject viewed the 0“ LED target were analyzed fiirther. Using the eye position data collected during fixation o f any other target was not possible due to a large confounding variable; when the arc perimeter was constructed, the LED targets may not have been positioned precisely every 10°. The 0° LED was the only target properly aligned with the center of ocular rotation and line of sight Table 3 J lists the data collected during the photographic and scleral search coü procedures that were relevant to determining the characteristics of ocular fixation in extreme-gaze. Whüe not a primary goal of the dissertation research, the feasibility of using subjects to calibrate the scleral search coü equipment was also investigated. For calibrating, search coü-based research has classicaUy relied upon mechanical devices specificaUy designed for the task.’’^“‘“-*^” As described in section 3.3, the device is rotated through an appropriate range of angles, and a calibration plot is produced of the equipment’s output signal as a fimction of rotation angle. In this study, the mechanical device was considered the gold standard with which to compare the subject calibration. A significant difference between the calibration slopes of the two sources would indicate scleral search coil slippage, eccentric fixation and/or errors in the positioning of the LED targets. These errors could be found in any scleral search coil study using human subjects for equipment calibration. Eye position data were also recorded for fixation in primary gaze during various head rotations. If present, eccentric fixation wotüd produce a significant di&rence between this eye position data and the eye position data recorded during fixation in secondary gaze with a head directed straight-ahead. Table 3.4 lists the data collected during the scleral search coil procedures that were relevant to determining the feasibility of human calibrations in search coü research. Overall, aü coUected data during the dissertation research were used in investigating characteristics of extreme-gaze ocular &cation and/or human calibrations.
46 ! A6Ec:
OCULAR HISTORY: * No binocular or monocular vision anomalies, complaints o f diplopia * No history of ocular disease, surgery or trauma
qnestibm r*^(»qj5tBttife.cpiidaroBsi;Cgptpmdicatihs«^^
ALLERGIES: * No allergic conditions which contraindicate contact lens or scleral search coil wear MEEHCAMONS: *^ame(fiiatmnswhi1d>entrtwmdiWfta>titaefefeii«EflC5aîIeraEsearcfecnilwegr REFRACTIVE ERROR: • Spherical equivalent refractive errors must be within ±1.00 Diopters, with < 1.00 Diopter of cylinder in the right eye. SMFLAMPEXmE ^MtMrhfefigftftfsigniffcaimeaitemflFantEihteniaBaBnormalitfes BINOCULAR VISION: * Subjects are required to have normal retinal correspondence * No eccentric fixation * Correctable visual acuity o f20/20 or better * Stereopsis of 40 seconds o f arc or better SEARCH c o m W B # ^MiisËteaSretatDfératBËweaEmgifrusscreraËseaicEbcoil
TABLE 3.1; Subject enrollment criteria.
47 MEAN AGE (RANGE): | *24.9 (22 - 28) years
ALLERGIES: * All subjects were &ee o f allergy conditions which would contraindicate contact lens or scleral search coil wear. Specific allergies included: seasonaL seafood, dust mites. Sulfa drugs and Penicillin. *Allsa^ecteMtereifiee;ofenedicatfoiBi\g6tcfewoafiiconttamdfcatecontact ^Ëais^pE scdliEal-seatBfiEcci^t^^ su^eets
MEAN REFRACTIVE • OD: - 0.02 DS - 0.22 DC x 096 ERROR: •OS: -0.06 DS -0.14 DC x 085 REFRAGTEEVEERReR^ RANGE:: M^#(kS(IKm-,(M»DexQ6#-(-0.7SDS> VISUAL ACUITY: • All subjects correctable to 20/15 OD and OS
ECCENTRIC FIXATION: •None detected ■*Bfong(fetectBtE GORECESBONEllENCEr SLIT LAMP EXAM: • All subjects were free of significant external and intemal abnormalities.
TABLE 3.2: Pre-study examination sample profile.
4S - : ■ —nn = 5 ^ 3 - — ■ “ 3Ü K
Series*: I 2 3 . 5 6 7 « 9 10 II 12 13 14 15 3" : "RrgceBbsWhm I OP OP !fciO^_ lOP r.,OP [OP i î K H pPïIS p- Head Position: 0" 0* 0* 10- HP HP 2(P 2(P 20" 30* 30* 30* 40* 40* 40*
I. Head positioned straight-ahead - '.trr
Target Position: O' O' O' O' O' # # E b s m n : i #
2. Head positioned at four different angles {without an afterimage) - ■ * r' r z ' SenesP*: ! I i * : . 5 7 & Target Position: O' O' O' O' O' O' O' O' If- '■ ' 'f ..... ' Hiea^ositünK; ; # Î Id t : '• w 30? : 4QP [ 40P
3. Head positioned at fonr different angles {with an afterimage) 1 S e n e ^ : ; s W . f Target Position: O' O' O' O' O' O' O' O'
3 ^ . i 40? * Sequence randomized ** Sequence identical to those utilized in the photographic equipment procedures, except the third measurements at each subject head angle and all 0° head angles were eliminated.
Table 33: Relevant data collected in investigating extreme-gaze ocular fixation characteristics. For each subject, data collection occurred during photographic equipment procedures (A) and search coil equipment procedures (B). During photographic procedures, a total of 15 photographs were taken (three at each gaze angle). A total o f5000 digital data signals were collected during 5 separate trials to measure the subjects “zero position” (Bl). 8000 digital data signals were collected during 8 separate trials to measure the subject's fixational position during 10°, 20°, 30° and 40° nasal eye rotations ^ 2 ). 8000 digital data signals were collected during 8 separate trials to measure the subject's fixational position during 10°, 20°, 30° and 40° nasal eye rotations with the use of an afierimage (B3).
49 Series:
i r.i " ■W-
1, Head positioned straight-ahead p- -.-r.- r-:; [ i Target Position: 10“ 20" 30“ 40“ I- ■ , ' ! 1 1 . # 3 .-ai
2. Head positioned at four different angles {yiithoutm. afterimage) t Series^: 1. : i Ï Ê 4 É 5 i « t 7 E » Target Position: 10“ 10“ 20“ 20“ 30“ 30“ 40“ 40“ 1 ■ ‘ r V: : Hea^oshmiK [ Iff* E Iff* : 20? ^ 2ÛP i # :: 4(T * Sequence identical to those utilized in the photographic equipment procedures, except the third measurements at each subject head angle and all 0° head angles were eliminated.
Table 3.4: Relevant data collected in investigating the feasibility of human calibrations in scleral search coil research. Data collection occurred during mechanical (A) and human (B) calibration procedures. During calibrations using a mechanical device, a total o f7000 digital data signals were collected during -10°, 0°, 10°, 20°, 30°, 40° and 50° rotations, 4000 digital data signals were collected during 4 separate trials to measure the subject's fixational position during 10°, 20°, 30° and 40° temporal eye rotations (BI), 8000 digital data signals were collected during 8 separate trials to measure the subject’s fixational position in straight ahead gaze during 10°, 20°, 30° and 40° temporal head rotations (B2),
50 FIGURE 3.1; The modified slit lamp equipment. The bite bar (I) and forehead rest (2) are seen to the right. Additional photographs and explanations of this equipment will be introduced m the setup procedures listed in section 3 J2.
51 FIGURE 3.2: Photographic parallax errors. This occurs during rotations o f the bite bar if the eye’s center of rotation (COR) is not coincident with the bite bar’s COR. This example illustrates the eye COR as a and the bite bar COR as an “X.” In (A), the eye is fixating straight-ahead at the LED target. In (B), since the COR of the eye and bite bar are separated, the eye is shifted laterally as the bite bar rotates clockwise. The eye must rotate left to maintain target fixation. This produces a different camera angle than in (A) and introduces parallax error.
52 FIGURE Eliminatioa of photographie parallax errors is attained with a movable LED/pinhoIe and camera arrangement. This example illustrates the eye COR as a and the bite bar COR as an “X.” In (A), the eye is fixating straight-ahead and the LED light is visible and centered through the pinhole, hi (B), after the bite bar is rotated clockwise, if the COR of the eye and bite bar are not coincident, the eye is laterally displaced. If the LED/pinhole and camera are then moved until the collimated I.RD light is again visible and centered, the same camera angle as in (A) is produced, eliminating parallax error.
53 FIGURE 3.4; Position of the bite bar/forehead rest when set at 0“ is shown in (A). An arrow highlights the bite bar. Position of the subject when the bite bar/forehead rest is set at 0“ is shown in (B).
54 FIGURE 3^; Positîoa of the bite bar/forehead rest when set at 40“ is shown in (A). An arrow highlights the bite bar. Position of the subject when the bite bar/fbrehead rest is set at 40“ is shown in (B).
55 FIGURE 3.6; Flowchart of the search coil equipment. Voltage signals originating at the scleral search coü terminate in the Tektronix monitor and the Pentium computer. Light emitting diode targets are controlled by the computer via a 16-bit digital-to-analog converter.
56 FIGURE 3.7; Bite bar equipment as viewed from the front o f the Helmholtz field cube. The bite bar has the adjustment capabilities to move in three dimensions (up/down, lefr/iight and fr)re/afr) as well as rotate through the center o f eye rotation over angles o f ±50°. The dental impression portion of the bite bar is highlighted by an arrow.
57 FIGURE 3.8; Slippage of the scleral search coil. Slippage is indicated when the linear horizontal distance firom a preselected limbal blood vessel to the search coil edge fainted black for clarity) changes over different viewing angles. For example, in (A), the subject is set at a viewing angle of 0“ (as in Figure 3.4), while in (B), the subject is set at a viewing angle of 40° nasal (an in Figure 3.5). The search coil slippage is temporal.
58 15%
g 10% -
EdI Iu 5% I 0%
S -5% —
I< % -10%
10.0 11.0 12.0 13.0
Bu l b a r C o n ju n c t iv a R adius O f C u r v a t u r e (millimeters)
FIGURE 3.9: Search coil slippage error plotted as a fimctioa o f bulbar conjunctiva (BC) radius of curvature (ROC). This dissertation assumed that the approximate BC ROC was 11.8 mm 6 r each subject Based on Equation 3.1, this figure quantifies the error (due to this assumption) in calculating search coil s%page for subjects with BC ROC other than 11.8 mm. For example, this dissertation underestimated the amount of search coil slippage by approximately 5% fi)r a subject with an 11.2 mm BC ROC.
59 0* 10" 20 * 30 ' 40
FIGURE 3.10: Measurement of the eye position during ocular fixations, where the subject’s head is aimed straight-ahead and stationary. LED targets were viewed individually in the following order: 0®, 10®, 0®, 20®, 0®, 30®, 0®, 40® and 0®. The subject’s left eye is shown occluded.
6 0 FTGURE3.il; Measurement of the eye position during ocular fixations, while the subject’s head is rotated in random order twice throughout angles o f 10°(A), 20°(B), 30**(Qand 40*’(D). At each head angle, two targets are viewed individually: (1) The LED directly ahead of the subject (e.g., the 30° LED for a 30° head rotation) and (2) the 0°LED. The subject’s left eye is shown occluded.
61 fT\rT\
FIGURE 3.12: Measurement o f the eye position during ocular fixations, while the subject’s head is rotated in random order twice throughout angles of IO“(A), 20“(B), 30°(Q and 40“^ ) . At each head angle, the 0“LED target is viewed. The subject’s left eye is shown occluded.
62 Figure 3.13; Schematic of the “plus-sfgn” afterimage utilized in the “Head positioned at four different angles {yvith an afterimage)” experiment described in section 3 A 2 , The overall outside diameter o f the afterimage was 2", and each arm was 15 minutes of arc thick. The subject’s fovea was undisturbed and centered within the 2 0 minutes o f arc afterimage-firee middle of the “plus- sign.” During the experiment, the subject centered the afterimage over the LED targets, hereby positioning the fovea directly over the LED.
63 CHAPTER4
RESULTS
4.0 INTRODUCTION To determine the characteristics of ocular fixation in extreme gaze, this chapter presents five sections. Scierai search coil slippage is described in section 4.1. Section 4 2 corrects the subject eye position data for scleral search coil equipment intrinsic noise, describes subject fixation èe/dre correction for search coil slippage and describes subject fixation q/ter correction for search coil slippage. Section 4.3 further analyzes subject fixation by describing the microsaccades and end-gaze nystagmus that occurred during data collection. Section 4.4 details eye movements associated with blinks. And section 4.5 investigates the feasibility of using subjects to calibrate the scleral search coil equipment. Figure 4.1 displays a flowchart highlighting the chapter sequence. For three of the ten subjects, the eye position data collected by the scleral search coil equipment were contaminated with low firequency, unstable noise. This intrinsic electrical noise could not be adequately filtered without also damaging true eye position data. Removal of the three subjects firom the study was required. However, this did not appear adversely to effect the study outcome. Only data of the remaining seven subjects will be presented below, and the effects of scleral search coil intrinsic noise will be detailed in section 4.2.1.
64 4.1 SCLERAL SEARCH COH. SLIPPAGE The scleral search coil was photographed under high-magnificatfnn while the subject fixated a single LED target in multiple nasal gazes (three times randomly over angles o f 0°, 10°, 20°, 30° and 40°). For each photograph, the linear distance was measured between the search coil edge and a pre-chosen limbal blood vessel. This linear distance was then converted into an angular position relative to the search coil position during straight-ahead gaze. In other words, the angular displacement (slippage) of the search coil was determined relative to the mean position of the search coil when the head was straight and the eye was fixating in primary gaze. For each subject, true slippage of the scleral search coil was estimated by the three search coil relative position measurements at each eye rotation angle. The goal of this section is to describe the scleral search coil slippage, if any, that occurred during nasal eye rotations.
4.1.1 DISTRIBUTION SHAPES AND INDIVIDUAL VARIATION Table 4.1 lists search coil relative position data for each nasal eye rotation angle. As mentioned, a subject’s search coil position during eye rotations was the difference between the mean search coil position at that gaze and the mean search coü position in straight-ahead gaze. By definition, the mean search coil position during straight-ahead gaze was 0 minutes of arc for each subject. From Table 4.1, it is apparent that during eye rotations, most of the subject’s mean search coil relative position data were non-zero and positive. This suggests that the search coil position often slipped temporally during a nasal eye rotation. For example, while Subject 1 fixated the LED target during a 40° nasal eye rotation, the search coil slipped an average of 79 minutes of arc temporally. Overall, search coil position increased temporally as the angle o f eye rotation increased: with nasal eye rotations o f 10°, 20°, 30° and 40°, the overall search coil position shifted temporally to 2.0,5.0,11.9 and 233 minutes o f arc, respectively. The overall standard deviations of search cod position also increased as nasal eye rotation increased: with nasal eye rotations of 0°, 10^, 20°, 30° and 40*, the overall search coü position standard deviations were 4.2,4.1,6.5,15.1 and 27.7 minutes of arc, respectively.
65 However this trend was not duplicated iu individual subject standard deviations, as they did not appear to change significantly over eye rotation angles. The increase in the overall standard deviations o f search coil position as the angle of eye rotation increased was due to the large variation in mean search coil positions between subjects. That is, for some subjects, search coil slippage increased as the angle of eye rotation increased but for other subjects it did no t Individual search coil position standard deviations were typically small. This suggested not only that search coil slippage was repeatable, but also that the measurement method was valid. Individual search coil position standard deviations ranged fiom 0.0 (Subject 4 during a 30® nasal eye rotation) to 14.1 (Subject 1 during a 30“ nasal eye rotation) minutes of arc. Kghty-nine percent of all values were less than 6.0 minutes of arc. No trend in standard deviation was apparent in the values for individuals over the range of eye rotations. Figure 4.2 illustrates the overall sample data with boxplots based on the median, 10*, 25*, 75* and 90* percentiles at each eye rotation angle. Visual inspection of the figure suggests a general increase in search coil slippage in the temporal direction with increasing nasal eye rotation angles. The data appear normally distributed with eye rotation angles of 20“ and less. With larger eye rotations, the search coil position data become skewed away from 0 minutes of arc. This skew is due to more extreme search coil slippage occurring for some subjects but not for others, as seen in Table 4.1 and Slippage Plots 1-7 (Appendix C). Slippage Plots 1-7 display for each subject the search coil relative position measurements at each eye rotation angle. A nonlinear regression was performed on the individual Slippage Plots 1-7 to describe the relationship o f search cod relative position to eye rotation angle for each subject. A model quadratic equation was found to fit the data.
Search coil slippage = (c,) * (Angle^ ) Equation 4.1
66 In this equation, is a constant for each individual. Angle was expressed in degrees and search coil slippage values were expressed in minutes of arc. Fitted quadratic regressions are superimposed over the subject data in Slippage Plots 1-7. Table 4.2 lists, for each subject, the value of c, and the respective standard error of the estimate. Sample c-values ranged from 0.00 (Subjects 2,4 and 7) to 0.05 (Subject 1). It is most apparent while comparing Table 4J2 with Slippage Plots 1-7 that search coil slippage occurs more in some subjects than in others. The most substantial search coil slippage was seen in Subjects 1,5 and 6 , where c-values were 0.05,0.03 and 0.02, respectively. Subject 3 demonstrated a small amount of search coil slippage, and consequently produced a c-value of O.Ol. No evidence of search coil slippage was foimd in Subjects 2,4 or 7. The main conclusions are that scleral search coil slippage occurred in at least three of seven subjects in this study. Also important was that for each subject at each angle of eye rotation, the standard deviations were typically small. This occurred even through the angles of eye rotation were randomized. The scleral search coil repeatedly slipped to a specific position for each nasal eye rotation in individuals. This measurement repeatability also demonstrates the validity of the Photography data collection technique.
4.1.2 SLIPPAGE STATISTICAL ANALYSIS This section attempts to create a model describing the overall scleral search coil slippage encountered in the study. Conceivable predictors of search coil slippage were: order of data collection, eye rotation angle, subject and interactions of the three. The effect of data collection order on relative search coil position was investigated. This was done to determine if the lens loosened up over time. Figure 43 plots the relative search coil positions as a fimction of order. Symbols are used to show data recorded from individual subjects. The data appear fiat except those of Subject I. The search coil appears to have slipped the most early in the data collection. This early infiated slippage for Subject I was probably due to the order of eye rotation angles; three of the first six eye rotation angles were at 40°, and one of the first six eye rotation angles was at 30°. Consequently,
67 overall search coil slippage did not appear to change over the 1 0 - 1 2 minutes of photographic data collection. Slippage was not systematically greater late in testing than early in testing. Using a repeated measures ANOVA in a balanced design, search coil slippage was analyzed as a fimction of eye rotation angle, subject and the interaction of the two. This analysis was considered a mixed model, as the 6 ctor subject was random and the factor eye rotation angle was fixed. The results are listed in Table 43. All terms were found statistically significant. Significance of eye rotation angle (p = 0.011) showed that scleral search coil slippage was associated with rotations of the eye. Significance of subject (p < 0.0005) confirmed that scleral search coil slippage was subject-dependant For some subjects, the search coil slipped more than in others (i.e., the heights of the lines illustrated in Slippage Plots 1-7 varied). Significance of the interaction of eye rotation angle and subject (p < 0.0005) showed that some subjects had larger unit increases of search coil slippage over rotations of the eye than others (/.e., the slopes of the lines illustrated in Slippage Plots 1-7 varied). In other words, a significant difference between the individual c-values exists. The main effects of subject and eye rotation angle could not be investigated further due to their interaction. The Tukey method of multiple comparisons was performed on the mean relative search coil positions over the five eye rotation angles. The results are listed in Table 4.4. With a 95% confidence interval of 7.64 minutes of arc, the mean relative search coil position measured at 30° was significantly different fix>m those measured at 0° and 10°. The mean relative search coü position measured at 40° was significantly different fit)m those measured at0°,10°,20°.and30°. Figure 4.4 plots all relative search coil positions measured over the range of nasal eye rotations. A best-fit nonlinear regression line was included in the plot. While the line displayed an increasing trend in overall slippage with nasal eye rotations, it did not take into account individual subject effects. Based on Rpiation 4.1, the overall c-value describing the overall search coil slippage over q^e rotation angles was 0.014. In summary, search coil slippage increased with the angle of eye rotatiorL Search coü slippage varied between mdividual subjects, and the rate o f mcrease in search coü slippage
68 with increasing eye rotation varied between subjects. Search coil slippage was not associated with order of data collection. With 95% confidence, significant search coil slippage occurred while subjects fixated nasally 30“ and 40“. With scleral search coil slippage quantified fi>r each subject, eye position data collected via the search coil equipment can now be assessed. Search coil slippage will be treated as a constant error (for each subject) within these data and will be removed from it in section 4 2 3 .
4 2 MACRO-ANALYSIS OF EXTREME-GAZE FIXATION Scleral search coil equipment was used to measure the position of the eye while the subject fixated a single LED target in multiple nasal eye rotation angles. The first series of measurements provided the subject’s “zero” eye position (Le., the mean fixational eye position with the head and eye straight-ahead). Individual “zero” eye positions were based on five data sets, each consisting o f960 digital signals collected over a 2 -second period. The second series o f eye position measmrements were taken while the subject fixated the LED target in multiple nasal eye rotation angles (Le., twice randomly over angles of 10“, 20“, 30“ and 40“). Here the subject fixated the target naturally. The final series of eye position measurements were taken while the subject fixated the LED target in identical nasal eye rotation angles and sequence as the previous data collection. The only difference between the previous series of measurements and this series was the use of a perifbveal “plus-sign” afterimage in the latter. Subjects fixated by subjectively centering the afterimage over the LED target. This method “forced” the fovea into a conjugate position with the target A significant difference fotmd between the two measurement series, without and with an afterimage, would suggest an eccentric fixation durmg the without afterimage method. The qre position data were filtered, corrected for search coil s%page and had blinks removed. These tasks are described in sections 4.2.1 ,4 2 3 and 4.4, respectively.
69 42.1 SCLERAL SEARCH COIL INTRINSIC NOISE Figure 4.5 plots the intrinsic noise of the search coil equipment These data were obtained with a search coil afhxed to a mechanical device specihcally designed for calibrating the scleral search coil equipment (described in section 3.2.2). The standard deviation of noise was approximately 4.1 minutes of arc. While the specific generator was unknown, there were several potential sources such as the search coil equipment pre amplifier, filter, transmission cables, and/or analog-to-digital converter. For each subject session, intrinsic noise was analyzed and reduced through filtering. To begin, a fast Fourier transformation (FFT) of the noise was performed. Figure 4.6 displays the spectral density produced after FFT of the noise shown in Figure 4.5. Two obvious peaks occurred at 354.5 and 468.8 Hz. This was a typical example; all noise had two dominant frequencies at approximately 350 ± 50 Hz and 440 ± 50 Hz. It should be noted that these two dominant frequencies within the intrinsic noise may have been, in actuality, closer to 850 Hz and 940 Hz aliased as lower frequencies. Aliasing is an error in frequency information due to a multiplicative relationship between sampling frequency and signal frequency. Shannon’s sampling theorem states that a signal of frequency F, can be reconstructed without error only if the sampling rate exceeds double the frequency (2F).*® If a frequency is undersampled, then aliasing occurs. For example, if a “’true” noise frequency occurred at 850 Hz and was sampled at 500 Hz, then the frequency would alias at (850-500 Hz) or 350 Hz. Since the eye is not normally associated with such high frequency oscillations, the two dominant frequencies were considered intrinsic noise within the eye position data. Therefore, after the FFT of the intrinsic noise, the two dominant frequencies were removed via filtering. Figure 4.7 illustrates the corrected noise levels of the scleral search coil system after filtering. The standard deviation of the noise was reduced from 4.1 to 0.32 minutes of arc. This noise level agrees with past reports of scleral search coil system noise.
70 Figure 4.8 plots an example of subject eye position data before (A) and after (B) noise reduction. An arrow in both graphs highlights how a small microsaccadic overshoot is only clearly seen after noise reduction. Filtering increased data clarity without sacrificing critical low frequency information: in this example, the mean eye position was revised from - 1 . 6 to —2 . 0 minutes of arc, and the standard deviation of gaze was reduced by approximately 10 times. More importantly, minute detail was greatly enhanced. A second example is shown in Figure 4.9, where noise filtering increased the clarity of end-gaze nystagmus without forfeiting low frequency information. Beats also appeared in the data, apparently from the addition of noise at two frequencies. Beats are apparent, for example, in Figure 4.8B after filtering of two dominant noise frequencies. Unfortunately, it was not always possible to remove all or even most of the intrinsic noise. Some of the search coil data were contaminated with a low-frequency "hum". This hum (at 3.25 - 3.76 Hz in Fig. 4.10) might be from an external source (e.g.. the line voltage arriving in the data record by means of a ground loop), or it might be an alias of noise at a much higher frequency. Either way, it is much higher-amplitude than the signal, it is not clearly separated from the signal in firequency, and its frequency was not even stable over time. Therefore, it could not be removed by selective filtering of the data. It was almost impossible to reduce the intrinsic noise adequately, because of this hum. Three data sets (out of the ten) were particularly intractable, so they were discarded entirely from ftnther consideration, including both photography and scleral search coil analyses.
71 4 ^ 2 FIXATION CHARACTERISTICS BEFORE CORRECTION FOR SEARCH COIL SLIPPAGE Raw eye position data were gathered directly fiom the scleral search coil equipmenL In this section, overall characteristics of this data will be discussed. None had yet been corrected fi)r search coil slippage error, but intrinsic noise had been band-filtered and blinks were removed. Due to the presence of search coil slippage, this section serves mainly to contrast section 4.2J. Fixation Characteristics After Correction for Search Coil Slippage.
4 2 2 .1 STRAIGHT-AHEAD GAZE For each subject, the average eye position while viewing the 0“ LED target in straight ahead gaze was considered their “zero” benchmark. A subject’s average eye position was calculated based on five data collections of 960 digital data points each. Throughout the scleral search coil procedures, all eye position data were relative to the respective subject’s “zero” eye position. Table 4.5 lists the precision of fixation for subjects while viewing the 0“ LED target in primary gaze. This was simply the standard deviation of fixation while the eye was fixating straight-ahead. Standard deviations averaged 4.6 minutes of arc, with a range of 1 . 8 to 7.0. This is consistent with past studies.*"'”**® Figure 4.11 illustrates the overall sample data via a boxplot based on the median, 10*, 25*, 75* and 90* percentiles collected during straight-ahead gaze. Visual inspection shows a normal data distribution balanced over the 0 minute o f arc eye position. This is expected, as all data were relative to the subjects’ “zero” eye positions.
4 2 2 2 FIXATION IN NASAL GAZE AFTERIMAGE Table 4.6 lists the fixation accuracy and precision of each subject during each nasal eye rotation angle (r.e., 10°, 20“, 30“ and 40“) without the use of an afterimage. This data group was not yet corrected for scleral search coil slippage, and therefore will not be analyzed in great detail.
72 The overwhelming majority (51 of 56) of fixation position means were positive. With this, the search coil equipment indicated that fixation was undershooting (/.e., lagging) the
0“ LED target. In addition, a consistent trend was seen with 6 of 7 subjects. Fixation lag increased as the angle of eye rotation increased; according to the scleral search coil, as the right eye was rotated more-and-more nasally, the fixation endpoint strayed finther and further to the right of target. An obvious example of this was seen in the data collections of Subject 1. While in a 10° nasal gaze. Subject I's mean eye positions were within 2 minutes of arc of the target center. In a 20° and 30° nasal gaze, the mean eye positions slightly undershot the target but remained within 12 minutes of arc. In a 40° nasal gaze. Subject 1 undershot the target center by over 90 minutes of arc (Le., > 1.5° ) in both cases. Only one of the seven subjects did not follow this trend. In the first data set collected on Subject 4, the mean fixational eye position during all four nasal eye rotation angles was consistently within 4 minutes of arc of target center. The second data set showed only a modest increase in fixation lag over the nasal eye rotation angles, with a maximum of 1 0 . 8 minutes of arc occurring during the 40° angle of gaze. These accuracy data are similar to those obtained by the pilot studies'^ and also by Ferman et al.^ while investigating the stability of human fixation during static head rotations. It should be noted that none of these studies corrected the eye position data for scleral search coil slippage. Ferman’s study was run under similar conditions as the present experiment; scleral search coils were used to monitor the position of the eye while subjects fixated a single forward-placed laser spot through static eye rotation angles between ±15°. They too found ocular undershooting of the target during eccentric gaze. Four of the eight subjects undershot the target by over 9.9 minutes of arc during 15° eye rotations. Two individuals undershot the target by over 2 0 minutes of arc during the 15° eye rotation. From Table 4.6, it is apparent that the overall mean eye fixation positions followed the same trend seen in most individuals. Fixation lag increased as the angle of eye rotation increased. On average, during eye rotations of 10°, fixation undershot the target center by 4.4 minutes of arc. Gaze undershootmg increased to means of 10.6 and 16.3 minutes of arc for eye rotation angles of 20° and 30°, respectively. During eye rotations of 40°, fixation lagged
73 the target center by an average of 37.9 minutes of arc. This is equivalent to fixating LI centimeters to the right of target at the I meter test distance. The overall standard deviation o f gaze also increased progressively with eye rotation. However this trend was not duplicated in individual subject standard deviations, as they did not appear to change significantly over eye rotation angles. The overwhelming majority of fixation standard deviations (49 of 56) were less than 7.0 minutes of arc. This agrees with fixation standard deviations measured during straight-ahead gaze. Of the seven (of 56) fixation standard deviations larger than 7.0 minutes of arc, four were associated with Subject I. The specific amounts were 9.7,12.2,10.8 and 14.4 minutes of arc for respective eye rotations of 10“, 20“, 40“ and 40“. As with other subjects, no trend was foimd in these standard deviations over the range of eye rotation angles. The larger fixation standard deviations for Subject 1 could suggest overall gaze imprecision outside straight-ahead. This would be easily accomplished with the presence of microsaccades or end-gaze nystagmus. Section 4 J, Micro-analysis of Bctreme-gaze Fixation, will investigate the gaze standard deviations of Subject I fiirther. Figure 4.12 illustrates the overall sample data as boxplots based on the median, 10"', 25"*, 75"* and 90"* percentiles collected during each of the four nasal eye rotation angles. Visual inspection of the figure suggests a general increase in gaze lag with increasing nasal eye rotation angles. In general, the data appear normally distributed with eye rotation angles of 30“ and less. With 40“ eye rotations, the fixation eye position data become skewed away fiom 0 minutes of arc. This skew is due to more extreme gaze lag occurring in some subjects, as seen in Table 4.6.
4 2 2 3 FIXATION IN NASAL GAZE IW Iff AFTERIMAGE Table 4.7 lists the fixation acctnacy and precision of each subject during each nasal eye rotation angle with the use of a perifi)veal afterimage. Again, this data group was not yet corrected &r scleral search coil slippage, and there&re will not be analyzed in great detail.
74 The majority (41 of 56) of fixation position means were positive, indicating fixation lags of the 0“ target All negative fixation position means (te., fixation overshoots) for the sample occurred with gaze angles of 1 0 “ and 2 0 “. Again, a consistent trend was seen in all individuals. Fixation lag increased as the angle of eye rotation increased; according to the scleral search coil equipment as the right eye was rotated more-and-more nasally, the fixation endpoint strayed further and further to the right of target. This is a similar trend to that found in the previous section, in the pilot studies and in Ferman et al. research.’ *® An obvious example was seen in the second data set collected on Subject I. While in a 10“ and 20“ nasal gaze, the Subject Ts mean eye position overshot the target center by 36 and 0.1 minutes of arc, respectively. In a 30“ nasal gaze, the mean eye position undershot the target by 48.2 minutes of arc. In a 40“ nasal gaze. Subject 1 undershot the target center by over 105 minutes of arc (/.e., > 1.75“). Overall mean fixation eye positions followed the same trend seen in most individuals. Fixation lag increased as the angle of eye rotation increased. On average, during eye rotations of I0“, fixation overshot the target center by 4.0 minutes of arc. Fixation lagged the target an average of 5.9 and 24.1 minutes of arc for eye rotation angles of 20“ and 30“, respectively. During eye rotations of 40“, fixation lagged the target center by an average of 42.8 minutes of arc. This equates to fixating 1.2 centimeters to the right of target at the 1 meter test distance. The overall standard deviations of gaze only modestly increased with eye rotation. Again, this was not duplicated in individual subject standard deviations, as they did not appear to change significantly over eye rotation angles. The majority (42 of 56) of fixation standard deviations were less than 7.0 minutes of arc. This agrees with gaze standard deviations measured during straight-ahead gaze and with those measured under the same conditions but without the perifoveal afterimage. Of the remaining 14 (of 56) fixation standard deviations larger than 7.0 minutes of arc, 6 were associated with Subject I. The specific amounts were 7.6,10.5,8.3,12.2,26.9 and 13.6 minutes of arc for respective eye rotations of 10“, 20“, 20“, 30“, 30“ and 40“. No trend was found in these standard deviations ovo^ the range o f sye rotation angles. Agam, the
75 prevalence of higher fixation standard deviations for Subject 1 could suggest overall that eccentric gaze was imprecise. This might be the result of microsaccades or end-gaze nystagmus. Section 43 ^ Micro-analysis o f Extreme-gaze Fixation, will investigate fiirther the gaze standard deviations of Subject I. Figure 4.13 illustrates the overall sample data using boxplots showing the median, 10* 25* 75* and 90* percentiles of the data collected at each of the four eye rotation angles. Inspection of the figure suggests a general increase in gaze lag with increasing nasal eye rotation angles. In general, the data appear normally distributed, with no extreme skewness.
4 2 3 FIXATION CHARACTERISTICS AFTER CORRECTION FOR SEARCH COIL SLIPPAGE Evidence was presented indicating that significant overall search coil slippage occurred while the lens was worn by study subjects. Remarkable also were the small standard deviations associated with the relative search coil position data over the eye rotation angles of individual subjects (Table 4.1). This suggested that while the scleral search coil may have slipped relative to the eye, it slipped repeatedly to approximately the same location for a given eye rotation angle. For example while in a 40° nasal gaze. Subject 5 showed an average temporal slippage of 44.3 minutes of arc, with a standard deviation of only 5.9 minutes of arc. Because of the repeatability of measured scleral search coil slippage, slippage was treated as a constant error in the subjects’ eye position data. Therefore, each subject’s eye position data were adjusted for that subject’s average search coil slippage measured at that particular eyt rotation angle. For example while in a 40° nasal gaze, the average slippage for Subject 5 was +443 minutes of arc (Table 4.1). That is, the search coil physically slipped on the right eye 44.3 minutes of arc toward the right. While in a 40° nasal gaze without an afterimage. Subject 5 showed a mean eye position o f+44.4 mmutes o f arc (Table 4.6). That is, the scleral search coil indicated that Subject 5 was fixating an average of 44.4 mmutes of arc to the right of the target Since the search coil equipment really only provided data detailing the position of the search coil, the average search cod slippage could be simply
76 subtracted ôoin the eye position data to provide the true estimated eye position. For Subject 5 while in a 40“ nasal gaze without an afterimage, the true mean eye position was, (+44.4) - (+44.3) = +0.1 minutes of arc. This section describes and analyzes true eye positions estimated over the range of eye rotation angles (i.e., 0“, 10“, 20“, 30“ and 40“). All of the eye positions below are corrected for search coil slippage.
42 J.1 STRAIGHT-AHEAD GAZE For both experiment procedures. Photography and Scleral Search Coil, all data were relative to measurements taken while the eye and head were straight-ahead. As mentioned earlier, the influence of search coil slippage was removed ftom individual mean eye positions by subtracting the respective mean search coil relative position. For straight-ahead gaze data, no correction was necessary for search coil slippage; by definition for individual subjects, mean search coil slippage during primary gaze was zero. Table 4.5 lists the individual and overall fixation standard deviations while subjects were in straight-ahead gaze. Figure 4.11 illustrates the overall sample data via boxplots based on the median, 10*, 25*, 75* and 90* percentiles. As described in section 422.1, this figure shows a normal data distribution balanced over the 0 minutes of arc eye position. Since all data were relative to the subjects’ “zero” eye position, this distribution is expected.
4222 FIXATION IN NASAL GAZE AFTERIMAGE Table 4.8 lists the fixation accuracy and precision of each subject during each nasal eye rotation angle (r.e., 10“, 20“, 30“ and 40“) without the use of an afterimage. Even after correction for search coil slippage, the majori^ (45 of 56) of individual fixation position means were positive. This suggested that overall, subject fixation really did undershoot the
0 “ target while in nasal gaze.
The fixation lag-with-Qfe-rotation trend seen in 6 of 7 subjects before correction for search coil slippage, was greatly reduced. Only 2 of 7 subjects continued to be associated with a gross increase in gaze imdershooting of the target over the ^ e rotation range. An
77 obvious example o f this was seen in the data collections of Subject 7. While in a 10“ nasal gaze. Subject 7s mean eye positions were within 8 minutes of arc of the target center. In a 20“ and 30“ nasal gaze, the mean eye positions undershot the target by approximately 13.5 and 25 minutes o f arc, respectively. In a 40“ nasal gaze, fixation lagged the target center by approximately 38.5 minutes of arc. The overall mean eye positions showed a marked improvement in accuracy compared with the same data uncorrected for search coil slippage (Table 4.6). While in a 10“, 20“ and 30“ nasal gaze, the overall mean eye positions undershot the target by an average of 2.4,5.6 and 4.3 minutes o f arc, respectively. During a 40“ nasal gaze, the overall mean eye position undershot the target center by 14.5 minutes of arc. This equates to fixating 0.4 centimeters to the right of target at the 1 meter test distance (compared with 1 . 1 centimeters based on uncorrected data). The overall standard deviations o f gaze were 7.0,7.5,18.4 and 15.8 minutes of arc for eye rotations of 10“, 20“, 30“ and 40“, respectively. The larger overall standard deviations with eye rotations of 30“ and 40“ were a result of wider spreads in individual mean eye positions, hidividual subject standard deviations were identical to those before correction for search coil slippage; slippage was considered a constant error in the data, which affected the raw mean eye position data, and not the standard deviations. Mentioned in section 42.2.2, individual standard deviations did not appear to change significantly over eye rotation angles, and the overwhelming majority (48 o f 56) of these were less than 7.0 minutes of arc. Figure 4.14 illustrates the overall eye position data via boxplots based on the median, 10'**, 25***, 75'** and 90*** percentiles collected during each of the four eye rotation angles. Inspection of the figure suggests a slight increase in gaze lag with increasing nasal eye rotation angles. The data ^p% r normally distributed with eye rotation angles of 10“, 20“ and 40“. The distribution is near-normal with 30“ eye rotations, however it has a long error bar in the overshoot direction. This is due to the unusually large overshoots seen in both data collections of Subject I. These are the only cases where removal of scleral search coil slippage actually worsened the estimated accuracy of ocular fixation.
78 4 :2 3 3 FIXATION IN NASAL GAZE FFZTff AFTERIMAGE Table 4.9 lists the fixation accuracy and precision of each subject during each nasal eye rotation angle (/.e., 10°, 20°, 30° and 40°) with the use of an afterimage. Even after correction for search coil slippage, the majority (38 of 56) of individual fixation position means were positive. This suggested that, overall, subject fixation continued to undershoot the 0 ° target while in nasal gaze. The fixation lag-with-eye-rotation trend seen in all seven individuals before correction for search coil slippage, was greatly reduced. Only one of seven subjects showed a gross increase in gaze undershooting of the target after correction. An obvious example of this was seen in the data collections of Subject 7. While in a 10° nasal gaze. Subject Ts mean eye positions were within 9 minutes of arc of the target center. In a 20° and 30° nasal gaze, the mean eye positions undershot the target by approximately 15 and 35 minutes of arc, respectively. In a 40° nasal gaze, fixation lagged the target center by approximately 52 minutes of arc. Overall, the corrected mean eye positions were more accurate than the same data uncorrected for search coil slippage (Table 4.7). While in a 10“ nasal gaze, the overall mean eye position overshot the LED target by 6 .1 minutes of arc. While in a 20° and 30° nasal gaze, the overall mean eye positions undershot the target by 0.9 and 12.2 minutes of arc, respectively. During a 40° nasal gaze, the overall mean eye position undershot the target center by 19.1 minutes of arc. This equates to fixating 0.6 centimeters to the right of target at the 1 meter test distance (compared with 1 2 centimeters based on tmcorrected data). The overall standard deviations of gaze were 16.4,15.5,13.8 and 30.0 minutes of arc for eye rotations of 10°, 20°, 30° and 40°, respectively. The larger overall standard deviation with eye rotations of 40° were a result of the wide spreads in individual mean eye positions. Again, individual subject standard deviations were identical to those before correction for search coil slippage; slippage was considered a constant error in the data, which affected the raw m%n sye position data, and not the standard deviations. Mentioned in section 42.2.3, individual standard deviations did not appear to change significantly over eye rotation angles, and the majority (42 o f 56) of these were less than 7.0 minutes of arc.
79 Figure 4.15 illustrates the overall eye position data via boxplots based on the median, 10“^, 25*, 75* and 90* percentiles collected during each o f the four eye rotation angles. This figure suggests a general increase in gaze lag with increasing nasal eye rotation angles. All data are near-normally distributed.
4J.4 EXTREME-GAZE OCULAR FIXATION STATISTICAL ANALYSIS This section attempts to create a model describing the overall ocular fixation positions measured over the four eye rotation angles. Conceivable predictors o f eye fixation position included; subject, eye rotation angle, presence/absence of afterimage and interactions among the three. First, interactions among the three factors were graphically analyzed. Interaction plots were created for each possible interaction: (subject x eye rotation angle), (subject x presence/absence of afterimage) and (eye rotation angle x presence/absence of afterimage). These plots are illustrated in Figures 4.16, 4.17 and 4.18, respectively. In each figure, interactions were demonstrated by graph lines having different slopes; a lack of interaction was indicated by parallel lines. Figure 4.16 shows the interaction plot of subject and eye rotation angle. Each line shows for individual subjects, the mean eye position over the range of eye rotation angles. All subjects appeared to have positively-sloped lines, indicating that with ascending eye rotation angles, the mean eye position shifted temporally. A gross différence between the slopes of subjects was not apparent; no significant interaction between subject and eye rotation angle was expected in the statistical analysis. Figure 4.17 shows the interaction plot of subject and presence/absence o f afterimage. Symbols show for individual subjects, the mean eye position associated with the presence and absence of an afterimage. All subjects appeared to have either a gentle upward or downward-sloping line. These slopes were different enough to question the presence of an interaction between subjects and the presence/absence of afterimages. Figure 4.18 shows the interaction plot of ^ e rotation angle and presence/absence of afterimage. Symbols show for each angle, the mean eye position associated with the presence
8 0 and absence of an afterimage. Again, all angles appeared to have either a gentle upward or downward-sloping line. These slopes were different enough to question the presence of an interaction between eye rotation angle and the presence/absence of afterimages. Eye fixation position was analyzed as a function of eye rotation angle, subject, presence/absence of afterimage, the interaction between subject and presence/absence of afterimage, the interaction between eye rotation angle and presence/absence of afterimage and the interaction between subject and angle using a three-factor ANOVA. The results are listed in Table 4.10. With p values of 0.763,0.214 and 0.691, respectively, no interaction term was found significant. Presence/absence of afterimage was also insignificant (p = 0.959), showing that the presence of an afterimage had no significant influence on the accuracy of ocular fixation. Presence/absence of afterimage and the three interaction terms were discarded fi'om the Eye Fixation Position model, and the analysis was repeated. Eye fixation position was analyzed as a function of subject and eye rotation angle. The results are listed in Table 4.11. The remaining terms were statistically significant. Significance of subject (p < 0.0005) showed that the eye’s fixation position varied by subject. Some subjects were more associated with inaccurate fixation than others. Significance of eye rotation angle (p < 0.0005) showed that the eye’s fixation position varied with angle of eye rotation. That is, fixation accuracy was dependent upon the amount of eye rotation. The Tukey method of multiple comparisons was performed on the overall mean fixation positions (/.e., both with and without an afterimage) over the four eye rotation angles. The results are listed in Table 4.12. With a 95% confidence interval of 15.1 minutes of arc, the mean fixation position measured at 40° was significantly different firom those measured at 0 “ and 1 0 °. Figure 4.19 plots the overall mean eye positions for individual subjects over the range ofnasal eye rotations. These plotted eye positions were the calculated means o f all data (f.e., both with and without afterimage) collected firom each subject at each eye rotation angle. A best-fit nonlinear regression line was included in the plot, based on the model quadratic equation:
SI Eye position = (c?) * (Angle* ), Equation 4.2 where is a constant. Angle values are expressed in degrees and eye position values are expressed in minutes of arc. With a c-value of 0.01, the line displays an increasing trend in overall inaccuracy o f gaze with nasal eye rotations. In summary, mean ocular positions became progressively more inaccurate during fixation of a target over increasingly nasal gaze angles. The position of the eye varied with angle of eye rotation and individual subjects, but was not significantly affected by the presence or absence of an afterimage. Failure to detect significance in the afterimage/no afterimage comparison suggests that subjects naturally utilized the fovea for fixation into extreme angles of gaze. Statistically, only ocular fixation during 40° nasal eye rotations was significantly difièrent firom ocular fixation in straight-ahead gaze.
4 J MICRO-ANALYSIS OF EXTREME-GAZE FIXATION This section analyzes subject eye position data fiirther by detailing more specific events that occurred during fixation. The most significant of these were microsaccades and end-gaze nystagmus. To begin, graphs of each subject’s eye position data over time are provided and described. Gaze Plots 1-7 of Appendix D display the eye position over time for Subjects 1-7, respectively, while fixating in primary gaze. Each plot contains five separate 2-second trials, represented by the labels A B, C, D and E. After the removal of any blinks (to be discussed), these data provided the “zero” benchmark information listed in Table 4.5. Gaze plots 8-14 display the eye position over time for Subjects 1-7, respectively, while fixating the LED target during a 10° nasal eye rotation without the use of an afterimage. Gaze plots 15-21 display the same, but while the subject fecated the target during a 20° nasal eye rotation. Gaze plots 22-28 display the same, but Wiile the subject fixated the target durmg a 30° nasal eye rotation. And Gaze plots 29-35 display the same, but while the
82 subject fixated the target during a 40“ nasal eye rotation. Each Gaze Plot 8-35 contains two separate 2-second trials, represented by the labels A and B. Gaze plots 36-42 display the eye position over time for Subjects 1-7, respectively, while fixating the I-ED target during a 10“ nasal eye rotation with the use of an afterimage. Gaze plots 43-49 display the same, but while the subject fixated the target during a 20“ nasal eye rotation with the use of an afterimage. Gaze plots 50-56 display the same, but while the subject fixated the target during a 30“ nasal eye rotation with the use of an afterimage. And Gaze plots 57-63 display the same, but while the subject fixated the target during a 40“ nasal eye rotation with the use of an afterimage. Each Gaze Plot 36-63 contains two separate 2- second trials, represented by the labels A and B. Immediately apparent within most plots are the normal micro-eye movements, slow drifts and microsaccades. Examples of these are provided in Figure 420. Here, a typical microsaccade (indicated by an arrow) moved the eye temporally by approximately 18 minutes of arc. After the microsaccade, a small corrective eye movements occurred to place the eye approximately 10 minutes of arc temporal to the target. Ocular drifts fisllowed, and slowly moving the eye in nasal then temporal directions. The third tyrpe of micro-eye movement, tremor, was not visible due to its small size (< 1 minute of arc). While inspecting the Gaze Plots, it is obvious that plots of the same subject were similar, like a fingerprint. For example, using Gaze Plots 8 (Subject 1) and 38 (Subject 3) as choices, it is not difficult to identify Gaze Plot 15 as Subject 1 and Gaze Plot 45 as Subject 3. A large portion of this within-subjects similarity was due to consistent intrinsic scleral search coil noise. For example, all data of Subject 1 contained small amplitude, periodic noise beats, while data of Subject 3 contained noise of higher amplitude and uniformity. However, much of the within-subject similarity was due to the subjects themselves. Overall, Subject 1 consistently produced moderate-amplitude microsaccades (—30 minutes of arc), and often produced end-gaze nystagmus during 40“ nasal eye rotations. Subject 2 data contained multiple saccade plateaus, where a second saccade often followed the first saccade after approxhnately 02-03 seconds. Subject 3 showed an ability to suppress microsaccades durmg focation. Subject 4 produced multq>le, isolated moderate-amplitude
83 microsaccades. Most of these microsaccades were followed with large corrective eye movements. Subject 5 suppressed microsaccades during fixation, and produced Gaze Plots similar to Subject 3. Subject6 was the least consistent of the seven subjects. Either the data showed isolated small-amplitude microsaccades, contained large saccade plateaus or microsaccades were completely suppressed. Subject 7 showed two patterns: microsaccades were either suppressed or the data was interrupted by isolated microsaccades with associated corrective eye movements. Upcoming sections will now describe and analyze the characteristics of microsaccades and end-gaze nystagmus that occurred during the dissertation research.
43.1 MICROSACCADE CHARACTERISTICS IN LATERAL GAZES Main sequence plots of peak velocity as a function of amplitude have been used extensively in the literature to identify and describe both saccades and microsaccades. The goals of this section are to present microsaccade characteristics from this dissertation research, and to compare them with main sequence plots of previous studies. Using a computer program which employed filters similar to those specified by Tole and Youngf®, microsaccades were identified based on a minimum peak velocity criterion of 12 degrees/second. While microsaccades can have peak velocities below this number^^, due to data noise, the incidence of false-positive identifications greatly increased with any reduction in the minimum peak velocity criterion. Microsaccade amplitude was considered the eye's total displacement as it passed outside the 95% confidence interval of eye positions immediately before the microsaccade, to the peak eye position ending the microsaccade. Corrective eye movements commonly occurred after the microsaccade. The final eye position after a corrective eye movement was also calculated; this was considered the eye’s position as it passed inside the 95% confidence interval of eye positions immediately after the corrective eye movement Since microsaccades typically have amplitudes below 25 minutes of arc, an upper- limit criterion of 50 mmutes of arc was selected. This excluded only two saccades from further analysis. Both were collected while subjects viewed the target during 10° nasal eye
S4 rotations with the use of an afterimage. The first occurred in Subject 2 in Trial A (see Gaze
Plot 37), and had a duration of 8 6 msec, amplitude of 963 minutes of arc and peak velocity of 46.0 degrees/second. The second occurred in Subject 7 in Trial B (see Gaze Plot 42), and had a duration of 18 msec, amplitude of 61.2 minutes of arc and peak velocity of 90.9 degrees/second. Both examples fit the main sequence of voluntary saccades. Tables 4.13-though-4.17 list the microsaccadic data collected while subjects viewed the 0“ target in nasal eye rotations of 0“, 10“, 20“, 30“ and 40“, respectively, without the use of an afterimage. These data correspond to Gaze Plots 1-35, Appendix D. Tables 4.18- through-4.21 list the microsaccadic data collected while subjects viewed the 0“ target in nasal eye rotations of 10“, 20“, 30“ and 40“, respectively, with the use of an afterimage. These data correspond to Gaze Plots 36-63, Appendix D. The most descriptive microsaccade information are duration (in msec), amplitude (in minutes of arc) and peak velocity (in degrees/second). These are highlighted in the tables. Mean microsaccadic durations were 15.1,17.4,16.6,17.7 and 17.4 msec during nasal eye rotations of 0“, 10“, 20“, 30“ and 40“, respectively, without the use of an afterimage. Mean microsaccadic durations were 19.1,17.8,14.0 and 17.5 msec during nasal eye rotations of 10“, 20“, 30“ and 40“, respectively, with the use of an afterimage. Figure 4.21 illustrates the mean microsaccadic duration during each nasal eye rotation angle for both the without and with afterimage conditions. Error bars show ±1 standard deviation for each duration mean. Inspection of the figure suggests that mean microsaccadic durations did not change over nasal eye rotations and were not influenced by the presence/absence of an afterimage. This is confirmed by the General Linear Model ANOVA listed in Table 4.22. Duration of microsaccades was analyzed as a fimction of subject, qre rotation angle and presence/absence of an afterimage. Withp values o f0.570 and 0.930, respectively, neither eye rotation angle nor presence/absence of an afterimage was found significant. Significance of subject (p < 0.0005) showed that the duration o f microsaccades varied by subject; some subjects were associated with longer durations than others. Mean microsaccadic amplitudes were 123,15 J, 20.0,16.8 and 17.1 minutes of arc during nasal eye rotations of 0“, 10“, 20“, 30“ and 40“, respectively, without the use o f an
85 afterimage. Mean microsaccadic amplitudes were 18.8,213,14.4 and 14.5 minutes of arc during nasal eye rotations o f 10®, 20®, 30® and 40®, respectively, with the use o f an afterimage. Figure 432 illustrates the mean microsaccadic amplitude during each nasal eye rotation angle for both the without and with afterimage conditions. Error bars show ±1 standard deviation for each amplitude mean, hispection of the figure suggests that microsaccadic amplitude did not change over nasal eye rotations, and that microsaccadic amplitude was not infiuenced by the presence/absence of an afterimage. This is partially confirmed by the General Linear Model ANOV A listed in Table 433. Amplitude of microsaccades was analyzed as a fimction of subject, eye rotation angle and presence/absence of an afterimage. With a p value of0325, presence/absence of an afterimage was not found significant. With a p value of 0.044, the inftuence of angle on microsaccadic amplitude was significant, however questionable; amplitudes may have increased with gaze angle. Significance of subject (p < 0.0005) showed that the amplitude of microsaccades varied by subject; some subjects were associated with larger amplitudes than others. Mean microsaccadic peak velocities were 24.6, 24.4, 32.7, 28.6 and 30.6 degrees/second during nasal eye rotations o f 0®, 10®, 20®, 30® and 40®, respectively, without the use of an afterimage. Mean microsaccadic peak velocities were 27.9,34.8,29.9 and 23.6 degrees/second during nasal eye rotations of 10®, 20®, 30® and 40°, respectively, with the use of an afterimage. Figure 4.23 illustrates the mean microsaccadic peak velocity during each nasal eye rotation angle for both the without and with afterimage conditions. Error bars show Standard deviation for each peak velocity mean. Inspection of the figure suggests that microsaccadic peak velocity did not change over nasal eye rotations, and that microsaccadic peak velocity was not influenced by the presence/absence of an afterimage. Again, this is partially confirmed by the General Linear Model ANOVA listed in Table 434. Peak velocity of microsaccades was analyzed as a function of subject, eye rotation angle and presence/absence of an afterimage. With a p value of 0.401, presence/absence of an afterimage was not ft)und significant With a p value of 0.049, the influence of angle on microsaccadic peak velocity was significant however questionable; peak velocity may have increased with gaze angle. Significance of subject (p < 0.0005) showed that the peak velocity
86 of microsaccades varied by subject; some subjects were associated with larger peak velocities than others. Figure 4.24 is a main sequoice plot of the peak velocity data (of Tables 4.13-through- 4.21) as a function of their respective amplitude. For comparison, Zuber and Stark’s main sequence plot o f microsaccades and saccades are also shown (firom Figure 2.3).^^ Zuber and Stark microsaccade data extended into smaller peak velocities than this dissertation’s equipment could permit, however data fiom the two sources are obviously comparable. The main sequence of the dissertation’s data fits neatly along a continuous curve with microsaccade/saccade date of Zuber and Stark and others.” "^ This supports the hypothesis that a single physiological system is responsible for the wide variety of saccadic eye movements. This plot also highlights the potential difficulty in classifying an eye movement as either a microsaccade or a saccade. To further the problem, Haddad and Steinman have shown that subjects can make voluntary saccades as small as microsaccades.^' Except two isolated saccades, this dissertation asstuned that the subjects used microsaccadic eye movements to maintain target fixation. Collectively, of the 145 microsaccades measured in the dissertation research, 93 (64%) were associated with a corrective eye movement. 60%, 67%, 69%, 75% and 70% of microsaccades were associated with a corrective eye movement during eye rotations of 0 ®, 10®, 20®, 30“ and 40", respectively, without the use of an afterimage. 44%, 50%, 75% and 64% of microsaccades were associated with a corrective eye movement during eye rotations o f 10®, 20®, 30® and 40®, respectively, with the use of an afterimage. The percentage of microsaccades associated with a corrective eye movement varied greatly by subject. Of all subjects. Subject 2 most consistently ended microsaccades without a corrective eye movement. In 59 microsaccades. Subject 2 produced only 25 (42%) corrective eye movements. Of all subjects. Subject 4 consistently ended 19 microsaccades with 19 corrective eye movement (100%). Other subject percentages fell between these two extremes: 8 6 %, 80%, 55%, 43% and 8 6 % of microsaccades were associated with corrective eye movements in Subjects 1,3,5 , 6 and 7, respectively.
87 la summary, microsaccade duration, amplitude and peak veloci^ varied by subject. Both amplitude and peak velocity varied with angle of eye rotation, but with p values of 0.044 and 0.049, this association was questionable. The presence of afterimages did not significantly affect any characteristics of the microsaccades. The microsaccadic main sequence of this dissertation fits neatly along a continuous curve with previous saccade and microsaccade data. This supports the hypothesis that saccades and microsaccades are controlled by a single physiological system.
4 J J END-GAZE NYSTAGMUS CHARACTERISTICS IN LATERAL GAZE End-gaze nystagmus occurred in two subjects, and only during 40“ eye rotations. While the nystagmus data were too small for statistical analysis, this section provides information detailing characteristics of the end-gaze nystagmus occurring during this dissertation research. The computer program that identified microsaccades (section 4.3.1) also identified the fast phase component of end-gaze nystagmus. Nystagmus was separated fiom the microsaccade data based on established criteria: jerk ttystagmus typically has amplitudes between 0.25 and 5 degrees, a frequency between 1 and 5 Hz and peak velocities of s 100 degrees/second.^ Visual inspection of the computer-selected eye movements confirmed the presence o f jerk nystagmus. Table 4.25 lists characteristics of the fast-phase component of end-gaze nystagmus present in the eye movement data. These data correspond to Gaze Plots 29,35,57 and 63 of Appendix O. The overall mean and standard deviations of duration, amplitude and peak velocity (in absolute values) are also listed in the table. These values are only slightly larger than overall mean of duration, amplitude and peak velocity for the microsaccade data (Tables 13-21). A significant detail is that the fast phase component of the nystagmus attempted to move the fi)vea closer to the target every time. Most cases supported the theory that saccades (r.e., the &st phase component of nystagmus) attempt to correct (fiifts of the eye (fe., the slow phase component of nystagmus), which take the eye away fiom the target and toward
88 primary gaze. This is most ^parent in Gaze Plot 29. However, Subject 4 showed a different pattern in Gaze Plot 32, Trial A. At approximately 0.55 seconds, slow phase nystagmus drifted the eye away from the target and primary gaze. Fast phase “corrective” nystagmus occurred at 0.73 seconds, and moved the eye back toward the target and primary gaze. This pattern was then repeated. This example was the opposite of expected: the slow phase of nystagmus drifted the eye away from primary gaze, while the fast phase of nystagmus moved the eye toward primary gaze. Additional research is required to fully investigate this unusual finding.
4.4 BLINKS The goal of this section is to present eye movements that occurred during frill or partial blinks. Data associated with these blinks were eliminated from all data analysis within the dissertation, but were left in the Gaze Plots for display. The identification of blinks was done by visual inspection of the Gaze Plots, based on the research of CoUewijn and others.^^ Collewijn measured human eye movements associated with blinks in six subjects via a scleral search coil technique similar to that used in this dissertation research. In addition, these eye movements were monitored in primary gaze and in lateral gazes (tl5 degrees). Blinks were consistently accompanied by transient downward and nasalward eye movements with amplitudes of 1-5°. Gaze eccentricity only modestly affected the eye movements, and mainly only the downward component. The Collewijn figures of eye movements associated with blinks have similar shapes to those eye movements friund in Gaze Plots 6 (Trial A and E), 39 (Trial B), 46 (Trial B) and
60 (Trial A and B). Gaze Plot 6 is Subject6 , while the remaining examples are Subject 4. These carmot be saccadic eye movements, as none have the necessary latency periods. There appear to be two patterns of eye movements associated with blinks. All examples began with the characteristic nasalward eye movement described by Collewijn. However after this movement, the eye either immediately returned to its original position (e.g:. Gaze Plots 39 and 60) or it overshot the origmal position and used a corrective
89 movement finally to return (e.g.. Gaze Plot 6 , Trial A). Some o f these eye movements are smaller than those specified by Collewijn as associated with blinks. This could be due to subjects only partially blinking dining the dissertation research; subjects were asked not to blink during the experiment. This is feasible since it has been shown that blinks and their associated eye movements initiate simultaneously.^ If a blink was initiated but quickly stopped, then it is possible that the eye movement was also abbreviated.
4.5 HUMAN CALIBRATIONS IN SCLERAL SEARCH COIL RESEARCH The goal of this section is to present human subject calibration data and to compare them to data produced by the search coil mechanical calibration device. For overall calibrations, this study relied upon a mechanical device specifically designed for the task. The device was rotated through a range of angles, and data were collected detailing the equipment’s output signal as a function of rotation angle. For comparison, human subject calibrations were also produced. Scleral search coil equipment was used to measure the position of the eye while the subject fixated individual LED targets (I) during temporal eye rotations while the head was fixed straight-ahead, and (2) during primary gaze while the head was rotated into temporal angles. The mechanical calibration device was considered the gold standard with which to compare the subject data. Table 3.4 illustrates the relevant data collected for calibration analysis. As described in section 32.2, data collected fiom the mechanical calibration device produced a simple linear regression for the plot of digital signal versus angle o f rotation. The slope of this regression line was used to calculate the magnitude of eye rotations for all subjects run during that particular day. This calibration technique was validated, as all regressions produced a correlation coefficient of 1.0. The digital signal data were converted back into “measured” coil positions, and thehr relationship to “ideal” coil positions was plotted in Figure 4.25 (squares represent these data). The slope of this relationship was 1.0. Human subject calibrations will be presented relative to this regression line of the mechanical calibration device.
90 Table 4 2 6 lists the mean fixation position (in degrees) of each subject during each temporal eye rotation angle I0“, 20°, 30° and 40°) while the head remained fixed straight-ahead. These data were not corrected fi>r scleral search coil slippage. Every fixation mean position undershot the ideal eye rotation angle, hi addition, a consistent trend was seen with all seven subjects. Fixation lag increased as the angle of eye rotation increased; according to the scleral search coil, as the right eye was rotated more-and-more temporally, the fixation endpoint strayed further and further to the left o f target For ecample, during 10°, 20°, 30° and 40° rotation demands, the mean fixational eye positions for Subject 1 were 9.80°, 19.00°, 27.48° and 34.86°, respectively. Overall mean eye fixation positions followed the same lag trend witnessed in the individuals. Fixation lag increased as the angle of eye rotation increased. On average, during eye rotations of 10°, 20°, 30° and 40° eye rotations, fixation undershot the target at positions o f 9.64°, 18.74°, 27.02° and 33.80°, respectively. Figure 4.25 illustrates the relationship of this measured search coil position to the ideal position (circles represent these data). Three confounding factors could have influenced this apparent lag of fixation away fiom the mechanical device calibration; improper positioning of the LED targets on the perimeter arc, search coil slippage and “optical sliding." Optical sliding was defined (Section 2.4) as retinal stretching or crystalline lens displacement secondary to eye rotations into extreme angles of gaze, which could affect the perceptual localization of the fovea in visual space. Table 4.27 lists the mean fixation position (in degrees) of primary gaze for each subject during each temporal head rotation angle (f.e., 10°, 20°, 30° and 40°). Again, every fixation mean position undershot the ideal eye rotation angle. A consistent trend was seen with all seven subjects. Measured fixation lag increased as the angle of eye rotation increased; according to the scleral search coil, as the head was rotated more-and-more temporally, the fixation endpoint strayed further and further to the left of target For example, during 10°, 20°, 30° and 40° rotation demands, the mean fixational eye positions for Subject 1 were 9.85°, 19.11°, 27.63° and 35.03°, respectively. The overall mean g e fixation positions followed the same trend witnessed in the individuals. Measured foration lag increased as the angle of head rotation increased. On
91 average, during head rotations of 10“, 20“, 30“ and 40“, fixation undershot the target at positions of 9.70“, 18.85“, 27.19“ and 34.45“, respectively. Figure 425 illustrates the relationship of this measured search coil position to the ideal position (triangles represent these data) Under this condition, only one factor could have influenced this apparent lag of fixation away firom the mechanical device calibration: improper positioning of the LED targets on the perimeter arc. During this data collection, the head and eye were always in primary position. This therefore eliminated the influence of search coil slippage (section 4.1.2) and optical sliding (section 42.2.1 ). If the LED targets had been perfectly positioned on the perimeter arc, in theory this calibration line would have exactly matched the mechanical device calibration. With no search coil slippage or optical sliding during this data collection, it can be assumed that fixation was accurate. Therefore, the LED targets were mislaid at approximate positions o f 9.7“, 18.9“, 272“ and 34.5“ during construction. Table 428 lists the mathematical difference (in minutes of arc) between the respective data of Table 426 and Table 427. Since the former was influenced by one factor (i.e., improper LED target positioning) and the latter was influenced by three factors (i.e., improper LED target positioning, search coil slippage and optical sliding), a difierence between the two describes the influences of search coil slippage and optical sliding at each target position. The overall mean differences between the eye fixation positions of Tables
4.26 and 427 were 3.6, 6 .6 ,102 and 39.0 minutes of arc for 10“, 20“, 30“ and 40“ target positions, respectively. Figure 426 illustrates the data of Table 428 via boxplots based on the median, 10***,
2 5 Ü1, 7 5 U1 9 Qih percentiles at each target position. It is interesting that data of section 4.2.22, Fixation in Nasal Gaze Without Afterimage [before correction for search coil slippage], were influenced by the same two factors [le., search coil slippage and optical sliding). Consequently, boxplots of Figure 426 resemble the boxplots of Figure 4.12. hi addition. Table428 corresponds to Table 4.6, where durmg qre rotations of 10“, 20“, 30“ and 40“, overall mean fixation lagged the ta^et by 4.4, 10.6, 16.3 and 37.9 minutes of arc, respectively. This comparison also suggests that optical sliding and/or search coil slippage occurs durmg both nasal and temporal eye rotations.
92 In summary, calibration data collected while the head was fixed straight-ahead and the eye was rotated through a range of lateral angles were confounded by the influences of target misplacement, search coil slippage and optical sliding. Calibration data collected while the eye was fixed in primary gaze and the head was rotated through a range of lateral angles were confounded by the influences of target misplacement A difference between the two conditions showed the amount of optical sliding and/or search coil slippage present in the experiment; as it had in section 4,22% measured ocular positions became progressively more inaccurate during fixation of a target over ascending gaze angles. It also appears that search coil slippage occurs in extreme nasal and temporal gazes.
93 SUBJECT 10" ! w 30" m em : SEk mean SD = meam ; SE> mean SD 1 mean? SEk I (ko : m 4.8 4.9 4 9 40.0 14.1 790 : 2 9 2 [ m 0.9 4 J [ 0 0 ■ 2 » 43 -0.9 : M
3 0.0 0.1 -0.9 1.6 ■ ; 4 3 4.7 4.3 8L5 1.5 4 0.0 4 J 0.9 7.5 t.0 4 3 0.9 0.0 5.7 33 5 (kO 5.9 4.7 1.6 13.2 ILS: 22.6 1.6 443 5.9
6 0.0 IS 3.8 1.6 : 13.3 4.9 m 9 4 4 7 m 2L& 0.0 2.8 : 42: 0.0 4.8 3 2
Overall: 0 : 0 1 4.2 2 . 0 4.1 5;0 6 S 11.9 15.1 2 33 27.7
TABLE 4.1: Search coil posMoa and standard deviation (minutes of arc) while viewing the 0° LED target during each nasal eye rotation. Positions are relative to the respective mean search coil position measured while the head and eye are directed straight-ahead (r.e., 0°). For individual subjects, each mean and standard deviation of search coil position is calculated based upon 3 measurements. Positive values indicate temporal search coil slippage.
94 SUBJECT StdErr I 2.6 X 10-^
2 5 tfeDft 0.9 X 10'" 3 o o t 1.4x10'" 4 o m 12 X 10'"
5 m 1.8 X 10" 6 0.9 X 10" 7 o m 1.0 X 10"
TABLE 4.2: Subject c,-values and standard error of estimates describing the quadratic regression fit of relative search coil position over eye rotation angles.
95 Analysis of Variance (Balanced Designs)
Factor Type levels Values Angle fixed 5 0 10 20 30 40 Subject random 7 1 2 3 4 5
Analysis of Variance for HinSlp S o u rce DF SS MS F P A ngle 4 7498.39 1874.60 4.14 0.011 Subject 6 8730.78 1455.13 57.11 0 .0 0 0 Angle*Subject 24 10868.11 452.84 17.77 0.000 E r r o r 70 1783.55 25.48 T o ta l 104 28880.83
TABLE 43: Repeated measures ANOVA describing relative search coil position as a function of eye rotation angle (/.e., “Angle”), subject and the interaction of the two.
96 9 ^ r ...... m .... ,,':i L m [ 30P m 2.0 (-5.6-9.7) 2 T 5.0 3.0 (-2.6-12.6) (-4.7 - 10.6)
1 3(P 113 93 6.9 (4J -19.6) (2 J-I7 .5 ) (-0.7-14.6) 40P 23J 113 18J 11.4 (15.7-30.9) (13.6-2 8 J) (10.7-25.9) (3.7-19.0)
TABLE 4.4; Tukey method of multiple comparisons comparing overall relative scleral search coil positions measured over each nasal eye rotation. The difference (in minutes of arc) between the mean relative search coil positions of the respective nasal eye rotations are listed in each comparison block. Within parentheses are the 95% confidence range of the difference between the respective mean relative search coil positions. Confidence ranges not including 0 . 0 minutes of arc indicate a statistically significant difference between the respective mean relative search coil positions. Blocks containing significant differences are emphasized in bold.
97 Su bje c t I 313
2 m 3 m 4 m 5 A3 6
7 2 5
Overall:
TABLE 4.5; Precision of fixation (minutes of arc) while viewing the 0“ LED target in straight-ahead gaze. The standard deviation of fixation fisr each subject is calculated based upon 4800 digital data points.
98 SUBJECT 1 # 2 0 ’ m 40’ : mean : setdev mean stddev mean se&d&f mean stddev I : -ZÇt 12 32 L . 91.8 10.8
I I .4 ^ : _ 112 122 i;, ,M :;„ 1052 14.4 2 ; 'LOt m 6.9 62 4® 252 5.8 2 y s ; f O 3.5 42 L 15.5 52 29.6 32 3 ».4 L6 13.4 12 1 14® f 2® 18.7 1.9 3 ; &3 ; M - 11.9 2.1 1 123 '■ 2 2 20.4 1.4 4 4.ft %» 0.8 4.7 22 -1.4 102 4 ■OJ 4 2 5.4 2.4 ; 6 7 ;; ^ 6 2 10.8 42 9 - ■ . .... 5 S2. 12- 15.1 4.7 ; 2®.l M 422 3.6 5 6 3 I 24 132 12 3t2 22 44.4 32
6 6 3 m 18.6 2.0 KH® t ! 2 282 4.7 6 ; && 4® 18.1 23 i 2®4 ■ 72 30.0 3.8 7 7.4 2 6 16.6 1.6 2 m \ 44 43.8 1.8 7 2 7 12.1 52 263 12 40.6 6.8
Overall: 4.4 i 1 0 . 6 7.5 163 1 1 .® 37.9 28.6
TABLE 4.6; Before correction for scierai search coil slippage: accuracy and precision of fixation (minutes of arc) without the use of an afterimage while viewing the 0“ LED target during each nasal eye rotation. Each subject mean and standard deviation of fixation is calculated based upon 960 digital data points. Positive values indicate gaze undershoots.
99 SUBJECT 20“ 40" mean stddev mean stddev r ■ V- ‘t I [ -iM ■i . -6.7 10.5 10.8 3.6 I ; : : -O.l 83 r 105.6 13.6 2 \ B&s ^: 2 m 11.8 5.8 38.4 8.0 r ...... 2 ! _ m -33 7.5 L.. ... L 33.4 6.4 3 ' -ftÿ 2.7 32 1.9 ' ' ' m ' 19.6 1.7
3 [ ■ -22 1.6 r # 212 2.1 4 ■ -m s ; 2.7 -17.0 9.4 6 3 [ 2 3 47.6 6.1
4 -MS -7.9 2.7 ■ &2 j Z 7 22.1 3.3 5 IS ; 19.1 1.8 Î 3 # : ' 44.3 2.6 5 : ÙS -4.9 5.9 4Eft r m 46.4 2.1
6 : 8101 302 5.0 2Z& \ M 42.8 2.6 6 -&s ' z * - 22.9 133 i 303 1 211 542 10.4
7 : && [ 2.0 22.1 1.5 ' 3 8 3 : : 3 3 ; 52.1 3.5
7 [ M 14.8 2.5 . Z1 58.8 32
. . -.. t •• ■ ■ O verall: L - # : 5.9 15.2 42.8 23.3
TABLE 4.7: Before correction for scleral search coil slippage: accuracy and precision of fixation (minutes of arc) -with the use of an afterimage while viewing the 0“ LED target during each nasal eye rotation. Each subject mean and standard deviation of fixation is calculated based upon 960 digital data points. Positive values indicate gaze undershoots.
ICO ; . SUBJECT ! ^ 1 2 0 " . j 40" mean stddev mean stddev
1 ■ ■ -6.4 33 [ . . # „ 12.8 10.8 I j ..:: 3.6 122 l-r M : 26.1 14.4 2 6.9 63 : ■ L 26.1 5.8 2 T : 3.5 42 ; SS ^ 303 33 3 [ 9 S ■ M : 8.7 12 : ' 2 0 102 13 Î . . is. 3 : W - 7 2 2.1 ■ «2- 11.9 1.4
4 1 3^ : 7 3 -I.I 4.7 ; .1 2 ;; [ # -7.1 102 4 • -1.0 4 2 3.5 2.4 5,0 6 2 5 2 42
5 I 1.9 4.7 [' # ;■: M -1.8 3.6 5 = 0.0 13 LM:: A...... r : ■ - - # - *■ 0.1 33 6 1 m : iJf': 12.0 2.0 i' ( M 3 5.5 4.7
6 i m r M : : U.5 23 m o 1 T^S 7.1 3.8 t 7 lA ' ^ 15.7 1.6 = 240 4A 40.1 1.8 7 0.0 I ^ 112 52 262: 13 36.9 6.8
O verall: : / I . m J 5.6 7.5 L m : 14.5 15.8
TABLE 4.8; After correction for scleral search coil slippage: accuracy and precision of fixation (minutes of arc) without the use of an afterimage while viewing the 0 ° T,KD target daring each nasal eye rotation. These data have been corrected for search cod slippage. Each subject mean and standard deviation of fixation is calculated based upon 960 digital data points. Positive values indicate gaze undershoots.
101 SUBJECT 20“ 40“ ^ , m e# ; mean stddev mean stddev
I r . -14.3 103 ^ m B M l -683 3.6 KIT"—" I L . .. ; -7.7 83 I « 2 26.6 13.6 2 11.8 5.8 L- .... L ' i- # : 393 8.0 2 -33 7.5 343 6.4 3 ^ 0.1 -1.6 13 y '- w ■ II.I 1.7
3 ' -M: : -6.9 1.6 : -jfcs , 4 t S 12.7 2.1 4 ; r w i -18.8 9.4 - Z» ' : 41.9 6.1 4 [ ■ ^ i m i -9.8 2.7 53 ] 2 ,7 " 16.4 3.3 5 \ : # ^ 53 1.8 ; # : ^ . 0.0 2.6 5 L L5 -18.1 5.9 I 3.S 2.1 2.1 6 : # [ I0i7 23.5 5.0 I i ' L* 20.0 2.6 6 , -9:1 m 163 13.5 : IT.E I ^ 31.4 10.4 7 213 13 LM.--. 48.4 3.5
7 ! 2 1 Ï : 133 2.5 55.1 33
Overall: -6.1 ! Î&A- 0.9 15.5 122 19.1 30.0
TABLE 4.9; After correctioii for scierai search coil slippage: accuracy and precision of fixation (minutes of arc) with the use of an afterimage while viewing the 0 “ T.RD target during each nasal eye rotation. These data have been corrected for search coil slippage. Each subject mean and standard deviation of fixation is calculated based upon 960 digital data points. Positive values indicate gaze undershoots.
102 General Linear Model
Factor levels Values S u b je c t 7 1 2 3 4 A n g le 4 10 20 30 40 AI 2 0 1
Analysis of Variance for EyePosn Source DF Seq SS Adj SS Adj MS F P S u b je c t 6 5516.0 5516.0 919.3 7.25 0.000 A n g le 3 2704.1 2704.1 901.4 7.10 0.002 AI 1 0.4 0.4 0.4 0.00 0.959 S u b je c t» A I 6 419.2 419.2 69.9 0.55 0.763 A ngle»A I 3 626.7 626.7 208.9 1.65 0.214 Subj ect«Angle 18 1797.9 1797.9 99.9 0.79 0.691 E r r o r 18 2283.7 2283.7 126.9 T o ta l 55 13348.0
TABLE 4.10; General Linear Model ANOVA describing eye position as a function of subject, eye rotation angle (ie., “Angle”), presence/absence of an afterimage (ie., “AF’), the interaction of subject and AI, the interaction of angle and AI and the interaction of subject and angle.
103 General Linear Model
F a c to r Levels Values S u b je c t 7 1 2 3 4 5 6 7 A ngle 4 10 20 30 40
Analysis of Variance for EyePosn S o u rce DF S eq SS A dj SS Adj MS F P S u b je c t 6 5516.0 5516.0 919.3 8.25 0.000 A ngle 3 2704.1 2704.1 901.4 8.09 0.000 E r r o r 46 5127.9 5127.9 1 1 1 .5 T o ta l 55 13348.0
Table 4»11:General Linear Model ANOVA describing eye posirion as a function of subject and eye rotation angle (i.e., “Angle”).
104 : W L . . 4 il. ■ i. ^ 1 u r -1.9 (-17.0 -132)
2(T 32 5.1 (-11.9-182) (-10.0-202)
m 82 102 5.1 (-6.8-23.4) (-4.9-252) (-IO.I -202)
m 16.9 18.8 13.7 8.7 (1.8-32.0) (3.7-333)) (-1.4-28.9) (-6.5-23.8)
TABLE 4.12; Tukey method of multiple comparisons comparing overall fixation positions (both without and with the use of an afterimage) while the subject viewed the 0 ° target during each nasal eye rotation angle. The difference (in minutes o f arc) between the mean fixation positions of the respective nasal eye rotations are listed in each comparison block. Within parentheses are the 95% confidence range of the difference between the respective mean fixation positions. Confidence ranges not including 0.0 minutes of arc indicate a statistically significant difference between the respective mean fixation positions. Blocks containing significant differences are emphasized in bold.
105 Trial Start Position Position Position .'T Time y ; Start End Final : ,:Il J A 1.42 -1.12 -1022 -4.97 A 1.72 -1.46 19.66 525 .....t T1 B 1.02 r ; 131 -7.00 -RKQ» -1.96 1 ■ : ! E 1.61 057 -12.57 0.92 1 2. . A 027 £ 13.68 -5.45 -5.45 2 " A 0.44 T' M. -0.01 21.86 21.86 2 A 0.71 ■ m . ■ 11.07 4.09 - # s ■ -2Œ29 4.09 2 B 0.46 I» : 437 -1.94 - m e ' -1.94 2 B 0.96 CM - ^ ^ -1.56 151 £ y m : 151 2 C 0.84 I 4.18 -10.04 !; ; ' ■ -10.04 ! 2 C 1.09 h. -7.65 1.13 1' ■ M S m 4 S 1.13 r-- C 158 -1.78 -1278 -2230r -12.78 F" 2 C 1.84 -10.85 -2.81 m m -2.81 2 D 0.79 24 -0.72 -10.86 ■; -IQII4 -153® -10.86 L z j :. D 1.68 -7.48 -121 L -m S k -121 i Z. E 120 m 2.19 -553 t.; L t. - I W ■ -524 4 A 0.49 14 -339 11.97 V æ m 1 29l4(I. 732 : 4 A 1.88 m 459 2837 L WMS t 11.15 I 4 ' ^ B 0.57 1.69 1521 L z s m . . , 8.89 ! I 4 C 0.76 12 231 27.10 r'2féï».: ' : 1125 " 1 4 C 1.41 14 -1.52 754 f ' à # ISnZS 329 4 D 032 \ I6i -4.76 1458 ' , I S # 3Î5I7 10.76 4 D 1.77 IS 0.19 23.84 £ 1522 r 4 E 054 I':. ■Ijfifc/V: -11.17 -20.92 -19.07 1 7 B 0.08 - -3.04 4.87 : Z m L : # I 4 ; 2.43 : 7 C 0.19 ; 1.16 -6.11 -239 ; 7 D 0.05 -7.73 7.41 M M ' 530 !.. : 7 E 0.18 :m : J 4.61 -435 -1.42 r- ; 7 ' E 1.65 W : -227 827 827 : .7 ‘ ‘ : E 1.94 n ; 053 -1954 r # # : ; ^ -17.74
Mean fabs): r. m : ' i: 2 W - . SD: N:
TABLE 4.13; Microsaccade data collected while viewing the 0° target in primary gaze.These data correspond to Gaze Plots 1-7, Appendix D. Start time, duration, amplitude and peak veloci^ units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak velociQf (absolute values) are also listed.
106 SuBgeet Trail Start Positioa Position Position Time Start End E :• f . l > 1 Final A 150 -129 -1834 -17.41 Ï, -..L, .. .:ï A 1.70 -1225 2824 22.51 Ï ' V:': B 0.68 11.41 -1255 -959 F - .«4 B 1.45 -0.73 2136 -524 ■ A 0.13 6.01 -3.17 -3.17 : ï ; -;: A 0.64 HE [.[6 16.32 15.45 : 2 A 0.71 [2.63 -12.89 L -12.45 : % A 0.89 -8.71 6.45 6.45 I: z A 1.04 r . W i t 356 -15.05 -14.48 ^ : Z ' ; A 1.54 -8.74 5.14 L m r n " : ' 5.14
Î 2 B 056 ■...... 324 -6.72 L , 1: -5.58 2 B 0.81 r M l : : -2.14 11.95 L. [ 2M 8 : 9.93 1 2 B 0.88 6.86 -1726 i . -1726 2 B 1.09 M m ' -10.04 6.17 r ; ■ : 5.96 ..K [ 2 B 1.44 353 -7.13 I T K # ' " -7.13 2 B [.68 25.88 536 6.06 L 3L : B 136 L I Æ .'l.. 7.07 10.13 I 'M m . .: 9.90 4 A 1.38 ; m i l : 1.13 1320 429 ir . -4. . B 0.46 .. 18 .... -6.59 1123 8.90 : ■ 4T\ :: B 1.71 é iim ' i... -0.88 6.00 L # # : : 4.82
s B 0.89 8 8.40 1.12 ^ -Tm -ISftSi 1.12 i 6 B [.41 L..... 18 8.71 16.84 L .m m . 16.84
: T A 0.86 r 81 . 6.87 1.13 L - . : 279 ! 7 B 022 L l i i ; 4.98 1353 1353
M ean labs): r . ; I 'zfeA: :
SD: . '7E8k - L L m # : ' : ;9E&. : N: ...:
TABLE 4.14r Microsaccade data collected while viewing the 0° target during a 10° nasal eye rotation, without the use of an afterimage. These data correspond to Gaze Plots 8-14, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak velocity (absolute values) are also listed.
107 SûBfe# Trial Start Position Position Position Time Start End Final
I . A 1.51 6.69 -10.72 : - m æ ;: : -7.66 r '' ; § : . ft- - , A 1.86 >r----- '-f 0.03 1544 L ; # # : 1.42 1 . B 1.42 1440 -11.43 -831 1 B 1.65 m ?::i -274 4438 L m & j 43.77 B 1.81 m 1 4539 14.62 14.78 A 0.95 , IS 10.47 29.64 29.64 f ' 2 ...■- A 1.02 20.95 -837 -4 s m -832 [ 2. A 122 fe . . m : -0.64 1339 [i'jfâü,:..... 1339 2 . ' A I.7I r - Mk ■ : 1270 339 i i m g . " ' ; 339 [ 2 B 0J8 I : 9.66 -0.73 g ; : # # ' ; : -020 [ 4 A 039 -0.66 1243 - ’ m m ÎÏS46- 11.90 i S A 128 r " j 1841 540 m m 6.78 7 B 0.46 i ‘ -Ml- ; 4.82 1836 [ -2 1 .^ - ,: 16.73
Mean labs): ' ... 2 @ .. : S2E2 SD: Ï W C z i : I # ; # 1 ' : N: I m . :.. m ' m
TABLE 4.15; Microsaccade data collected while viewing the 0“ target during a 20“ nasal eye rotation without the use of an afterimage. These data correspond to Gaze Plots 15-21, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall m%n and standard deviations of duration, amplitude and peak velocity (absolute values) are also listed.
108 Trial Start Positioa Positioa Positioa Time Start Eod Fiaal A 0.42 . / m i r j 13.80 -11.63 -1028 J A 1.88 L :M ■ : 6.68 -922 -622 B 0.66 L m , : 1528 -4.14 r a m È : : -0.83 ' 2 : A 1.18 m . ; 1621 26.64 .IdbS 26.64 ' 2' : A IJ7 Ti' : M . " : 23.12 16.98 r - i m 1722 2 j B 022 15.63 2I.II 20.61 2 B 0.85 L... .2%L__ ; 11.75 23.81 L ififisr 23.81 2. : B 0.99 l a m 2027 10.00 i - m m - N im s 10. II 2 B 1.46 !: ' Ï& 10.75 1728 ' s m m a : 17.06 2 B 1.66 m . : 14.44 2.71 Ï - i i : b 4.19 2 B 1.91 E— 7.11 30.57 { 2 3 Ê S . ' 30.57 4 A 0.64 I: W 4.07 21.06 ^ m » 2.44 : 4 A 124 - -2.13 21.48 " : I W k : : 1328 4 B 0.77 I: 3.57 3522 t . ï j s m . 18.45 5 B 022 30.08 2620 .. 28.41 s B 1.49 w . : 33.01 26.76 I M m 27.03 ^ 6 A 127 is ; 1720 43.81 " a m : Ï 3820
6 . A 120 É m 3126 -15.76 r Æ & i M m -15.76 6 A 1.86 " 16 -5.74 19.18 : 2 m t Sf.75 19.18 ! 6 B 126 IS 28.00 5226 2S5& m m 51.15 i s B 1.81 i im . .. 42.07 3020 3020 7 A 0.17 Ï ' M ; 13.65 28.73 L C M # " :r m # " 24.49 7 A 020 i..... m . : 3029 1222 F ' T # # ' 1723 7 A 1.73 m - 2225 29.00 m o s 27.42
Mean tabs); EEÎ - ■; I6t& : ZS6 : ■ g " SD: ' « Ê t . N: : m ■ m '
TABLE 4.16; Microsaccade data collected while viewing the 0° target during a 30° nasal eye rotation without the use of an afterimage. These data correspond to Gaze Plots 22-28, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes o f arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak veloci^ (absolute values) are also listed.
109 Trial Start Positioa Positioa Position Time Start End Final r Z 1 A 0.70 r : 20.44 3156 b isiïÊ L i 30.88 L - z v . ' ; A 0.97 L 30.14 21.99 23.06 Ï A 0.49 22.98 -16.71 -10.44 ; 4 / B 1.57 ' m \ 5.07 22.19 15.78 . 5- A 125 L. z m j 44.05 38.14 38.14 ■ s- : ' - B 020 4750 36.18 39.40 Ï' i A 1.60 28.04 16.65 16.65 G B 126 F 2659 38.95 E -msiSr': ; m i# 38.95 7 B 021 57.45 26.64 - w m " ' : - a m # 33.85
7 B 1.51 ' m . 40.94 17.48 ^ -m m 28.99
b. .... - -■ Mean tabs): ... r ;
SD: ;r.. im * : . ..
N: ' . m . m
TABLE 4.17; Microsaccade data collected while viewing the 0“ target during a 40® nasal eye rotation without the use of an afterimage. These data correspond to Gaze Plots 29-35, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject's “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak velocity (absolute values) are also listed.
n o swajgec# Trial Start Position Position ' ■ Position Time Start End m adÊ s^ Final ' I : A 0.13 2024 -12.89 r \ # 2 3 _ : : . I - m m .. -10.56 1 A 1.93 -7.16 -29.04 ■l.rmM- -27.19 2 A 026 II25 -6.15 -6.15 2 . A 0.77 -14.48 -57.61 I. . i ; -57.61 2 ; A 122 4322 1629 CTW#:: 16.39 i B 0.51 -4.02 -9.72 a m . -9.72 i 2 : B 0.71 r " m :: -7.94 1.84 J 1.66 i ÎA 027 » 2.18 8.50 L m m 6.51 3 B 0.71 " 12 -0.05 4.74 ; 13.71 4.74
Mean tabs); i m i :&8i : m . » SD: r j ü s
N: Ï" W ~ '" i: ..-Jf ,
TABLE 4.18: Microsaccade data collected while viewing the 0“ target during a 10° nasal eye rotation with the use of an afterimage. These data correspond to Gaze Plots 36-42, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes o f arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak veloci^ (absolute values) are also listed.
I ll w w Trial Start Positioa Positioa V i m ! Positioa Time Start Ead Final ■ A 0.88 l: : 2.66 11.02 1022 A IJ3 L_ M 123 -2226 -2226 t '• B 0.67 16 6.67 -1539 r -sEifik : -15.59
. 2. A 0J7 L 1224 120 ■ 420 '2 ■; A 0.70 r a g 4.46 19.03 :.. 17.76 2 A 125 : È r 12.89 3.95 325 ; 2 B 025 i:: m . / ; 3.13 -6.72 : ^ . 1 -22SI' -6.72
2 B 1.47 : _ M : -721 2320 ; . 3#% . 2320
2 B 1.55 ■ -M ..... 19.70 -8.63 V S ^ . z -639 3 A 0.90 [ ' : Æ r i 6.34 1635 V 8.93 : 4 A 0.44 ' I -2831 16.99 ïV m m V . 126 ; s B 0.89 m ■ -135 9.74 m # 2 s m 9.74 : 5 , B 1.19 2.84 -12.98 r Tm80L . -1228 s B 122 m 27.87 47.75 M m . 45.65 B 1.58 ! . # J 4132 5.64 5.64 6. B 1.78 1 m 1138 54.89 I M m ' 48.03
Mean tabs): 2 ilé 3m& SD: m I . ■
N: '■ m m ...'m '" ‘
TABLE 4.19: Microsaccade data collected whüe viewing the 0“ target during a 20“ nasal eye rotation with the use of an afterimage. These data correspond to Gaze Plots 43-49, Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations of duration, amplitude and peak velocity (absolute values) are also listed.
112 SuBfect Trial Start Position Position Position
Time E. . Start End Final I A 1.41 54.84 24.48 24.48
2 A 1.58 s . .. I8Z2 8.00 r l i m .: 8.01
„2 . B 029 . s 15.00 9.80 f m r n 11.71 ZB 1.69 - 16 1133 2437 [ i6J& 22.96 4 B 1.05 [...T6 : 3.49 30.48 I I 10.67
5 A 0J3 1: M 34Z1 22.46 - m m . J L m r n : . 24.42 5 . . B 029 Î ' J 49.07 3734 L a e s E :" ! 40.46 ' 6 B 0.96 M ' - 23.03 16.79 - i ^ 26.13
Mean tabs): ! MOr : 20® SD: !' ^ ' ■ ; lOlZ^ N: R ...... R .....
TABLE 4.20; Microsaccade data collected while viewing the 0“ target during a 30“ nasal eye rotation with the use of an afterimage. These data correspond to Gaze Plots 50-56, Appentüx D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s ‘"zero” eye position. Overall mean and standard deviations of duration, amplitude and peak velocity (absolute values) are also listed.
113 Triai Start Positioa Position : m m Position
Time Start End ■ . V d b m r Final 2 A 024 ' m 3137 41.64 r , m e , [ m o z 41.64 2. A 0.65 L.. 36.55 28.88 30.68 2 A 133 37.81 53.42 [ : 5236 2 A 1.62 i..: Ist.;.. 54.85 43.51 r ■ 4332
2 B 033 , m ...... 3839 25.18 m a • M m . 27.81 2 B 0.72 r 2a 2236 36.68 U33L I m e s 35.88
Ï 2. B 1.85 Ï 26 3932 23.88 _, I M s s 23.88
I Î B 0.51 [ 6 2134 30.48 ' ' t m s 6 , 2431 5 , B 0.68 4638 42.38 I 42.38 S & B 1.49 $2 5435 3634 r -m m ' ' r # # 36.54 6 B 1.61 4139 8237 L 4Ô9& s& m 78.07
Mean labs): ' m s 1 . . M S. ! 2 S 2 SD: r r w t I 3 N: 11 . n II
TABLE 4.21; Microsaccade data collected while viewing the 0" target during a 40° nasal eye rotation with the use of an afterimage. These data correspond to Gaze Plots 57-63, Appendix D. Start time, duration, amplitude and p ^ velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subject’s “zero” eye position. Overall mean and standard deviations o f duration, amplitude and peak veloci^ (absolute values) are also listed.
114 General Linear Model
Factor levels Values S u b je c t 7 1 2 3 4 5 6 7 A ngle 5 0 1 0 2 0 30 40 AI 2 0 1
A n a ly s is of Variance for D u ra tio n S o u rc e DF Seq SS Adj SS Adj MS F P S u b je c t 6 1605.93 1605.98 267.66 5.89 0 . 0 0 0 A ngle 4 142.07 133.40 33.35 0.73 0.570 AI 1 0.35 0.35 0.35 0 . 0 1 0.930 E r r o r 133 6041.61 6041.61 45.43 T o ta l 144 7789.96
TABLE 4.22: General Linear Model ANOVA describing the duration of microsaccades as a fimction of subject, eye rotation angle {Le., “Angle”) and presence/absence of an afterimage {Le., “AF’).
115 General Linear Model
Factor Levels Values S u b je c t 7 1 2 3 4 5 6 7 A ngle 5 0 1 0 2 0 30 40 AI 2 0 1
Analysis of Variance for Amp S o u rc e DF Seq SS Adj SS Adj MS FP S u b je c t 6 3433.31 3617.54 602.92 8.55 0 . 0 0 0 A ngle 4 1004.88 711.19 177.80 2.52 0.044 AI 1 104.96 104.96 104.96 1.49 0.225 E r ro r 133 9382.49 9382.49 70.55 T o ta l 144 13925.64
TABLE 4.23; General Linear Model ANOVA describing the amplitude of microsaccades as a function of subject, eye rotation angle (Le., “Angle”) and presence/absence of an afterimage (f e., “AI”).
116 General Linear Model
Factor Levels V a lu e s S u b je c t 7 1 2 3 4 5 6 7 A ngle 5 0 1 0 2 0 30 40 AI 2 0 1
A n a ly s is of Variance for PeakV el S o u rc e DF S eq SS Adj SS Adj MS FP S u b je c t 6 4938.76 4645.29 774.22 8.27 0 . 0 0 0 A ngle 4 1227.47 915.54 228.88 2.45 0.049 AI 1 66.35 66.35 66.35 0.71 0.401 E r r o r 133 12444.08 12444.08 93.56 T o ta l 144 18676.65
TABLE 4^4; General Linear Model ANOVA describing the peak velocity of microsaccades as a function of subject, eye rotation angle {Le., “Angle”) and presence/absence of an afterimage {Le., “Ai”).
117 ; Siifij;ee£ Trial After Start Buamtibm Positioa Positioa Amg#adb image Time Start Ead %lbc%F A No 0.04 99.11 6227 ; 4 a m : * . 1 A No 0.S6 J 112.83 81.99 1 -3ft8!4 ; : -3S3S IA No IJ6 : : 106.55 8425 i -223ft
E A No 1.65 L " 102.75 HAS 1 -2 s m - - 2 ^ I A No 1.94 z z 99.49 82.01 ^ -1748 -2ft.64 IB No 026 121.83 95.44 [ -m ift : % , I B No 052 2S 11523 69.41 ! I B No 091 24 111.62 68.07 -<&35 i B No 1.54 2Z 136.62 8338 ‘ -5451 1 I B No 1.84 1 zz 110.46 76.19 \ -3427 ; -4135
Î B Yes 0.53 24 12633 101.11 i -25.06 IB Yes 1.09 ■ # 109.95 89.76 ; m i f t -285ft I B Yes 1.61 2ft 9752 75.85 - 3 f t^
4 A No 0.73 1 -16.60 -3.51 1 m # L : ; # k r"‘ ...... 1 4 A No 0.97 ; 14 -13.01 2.97 ; E&% r 2&# 4 A Yes 135 2ft 55.12 43.07 ■ -tZftS -202.7 4 A Yes 1.90 r 2ft 58.66 44.85 ; -13M -1838
Mean fabsl: ..ZÈ8L. J 1..3 m ...... SD ! 3 # " r mm : IftT N !. m Ï m
TABLE 4.25: Characteristics of the fast-phase component of end-gaze nystagmus. Nystagmus occurred in two subjects, but only while viewing the 0° target during 40° nasal eye rotations without and with the use o f an afterimage. These data correspond to Gaze Plots 29,35,57 and 63 of Appendix D. Start time, duration, amplitude and peak velocity units are seconds, milliseconds, minutes of arc and degrees/second, respectively. Position data are relative to the respective subjects “zero" qre position. Overall mean and standard deviations o f duration, amplitude and peak velocity (absolute values) are also listed.
118 Su b je c t m 2 0 “ 30t 40“ I 19.00 23t4S 34.86
2 18.65 33.86 3 18.53 Ï # # 33.51 4 9:67 18.79 : m 31.34 ! 5 18.47 ; 26.5» 33.40
6 i 9i6S 18.93 2755 35.11 7 18.83 34.53 9M [ .. .
Overall: ! 18.74“ i 33.80“
TABLE 4.26: Mean fixation position (in degrees) o f each subject during each temporal eye rotation angle while the head remained fixed straight-ahead. Each subject mean is calculated based upon 960 digital data points.
119 r Su b je c t 20" w
I I9.II . ## 35.03 2 18.67 L # # ... 3351 3 9 # 18.66 33.80
4 9 m 18.88 2T.B .... 34.29 5 18.60 . ■ 2 iS m "' 3351 6 a ^ 19.II 2 m 3534 7 18.92 27AI 34.85
O verall: 18.85" J 34.45"
TABLE 4.27: Mean fixation position (in degrees) of primary gaze for each subject during each temporal head rotation angle. Each subject mean is calculated based upon 1920 digital data points.
1 2 0 Subject 2 0 “ 40“
I L. 6.6 m 1 0 2
2 : : 12 : m 3.0 3 42 7.8 .. 17.4
4 5.4 1 2 1 0 177.0 5 m 7.8 i # ■ 30.6 6 m - ' 1 0 .8 f; -/M 13.8
7 ’ ' - ■ 5.4 -1 IÆ ' 192
Overall: - 3 ^ 6 . 6 I 39.0
TABLE 4.28; The mathematical drfiference (minâtes of arc) between the respective data of Tables 420 and 4.21. These inaccuracy data describe the influences of search coil slippage and subject eccentric fixation at each target position.
121 4J Sefecaf SearebrCoilS^sage » Quantités sampfe
MlBcro-aiia^^snofEMrenie-gazeFbEatHiD » Cocrects subject datar&r sckral seatcb coS equipment mtsmsicnoise
Macro-ana^s» o f Extrane-gaze Fixation * Describes subject âcarion: collection fer slippage
4 3 .1 Micro>aiiafysi4afExtreme-0UEe^Fixatfon< *- Describes subject microsaccacfes 4 .1 .^ Mfcco-aiia^ni»of l^rtreme-ffueeFfaoitfoit »D(escribes subject end-gazeo^stagmus 4.4 Blinks •Corrects subject data k>r eye movements assocÎBteé with bimks 4 3 Human Calibrations •bivestigatesthe fiasibfli^ofusmgsubiectsto^ calibrate tbe scleral search co&eqp%ment FIGURE 4.1; Flowchart of the Results chapter. Each block indicates the chapter section and an abbreviated section goal 122 < u. O z I I ■ r 8 i I u > I -10 10 20 30 40 50 E y e R o t a t io n a n g l e (degrees ) FIGURE 4.2: Overall search coil positions while viewing the 0“ target during each nasal eye rotation angle. These positions were relative to the mean search coil position measured while the head and eye were straight ahead. The median, 10th, 25th, 75th and 90th percentiles are represented as boxes with error bars. Positive position values indicate temporal search coil slippage. 123 Subject t 80 Subject 2 < Subject 3 o Subject 4 5 Subject S ë □ Subject 6 60 ♦ Subject 7 o 40 I.j g 1 20 %2 (d > I 5 I S -20 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 D a t a C o l l e c t io n O r d e r FIGURE 4J; Measured search coil positions as a function of data collection order. Each position was relative to the subject's mean search coil position while the head and eye were straight-ahead. Positive position values indicate temporal search coil slipp%e. 124 < 80 tu 0 5 60 1 % 2 0 2 _i 0 5 Œ - 2 0 y < -40 u CQ M -60 I -80 g * -100 0 1 0 20 30 40 50 E y e R o t a t io n a n g l e (deg rees ) FIGURE 4.4; Overall search, coil positions while viewing the 0“ target during each nasal eye rotation angle. Positions are relative to the mean search coil position for individual subjects while the head and eye were straight-ahead. The best-fit non-linear regression line is also shown. Positive position values indicate temporal search coil slippage. 125 y < Cb 0 z 1 V3Cd 5 z T im e (seconds ) FIGURE 4.5; Intrînsîc noise of the scleral search coil equipment collected during calibration procedures. The standard deviation of noise was approximately 4.1 minutes o f arc. 126 2500 2000 t 1500 z fid Q j 1000 « : & 500 0 100 200 300 400 500 F r e q u e n c y (Hz) FIGURE 4.6: The spectral density produced after fast fourîer transfomiatioa of the intrinsic search coil equipment noise seen in Figure 4.5. The two most dominant peaks occur at 354.5 and 468.8 Hz. Due to the 500 Hz sampling âequency, these peaks are aliases of the true dominant noise fiequencies o f854.5 and 968.8 Hz. 127 40 ^ 2 0 < u. O 0 5 w -2 0 u 22 O -40 Z -60 -80 -100 0 1 2 T im e (seconds ) FIGURE 4.7: Corrected noise levels of the scleral search coil equipment after the mtrinsic noise (seen in Figure 4.5) was band-filtered of its two dominant ftequencies (seen in Figure 4.6). The standard deviation of noise was reduced ftom 4.1 to 0.32 minutes of arc. 128 I o 2 1 0 2 .20 I -40 I -60 .0 0 .100 0 1 2 U 40 0 20 1 ” 2 .20 £ -40 I -60 .too 0 t 2 TIM E (SECONDS) FIGURE 4.8: Example of eye position data before noise correction is shown in (A). Tbe same data after band-filtering of the two dominant noise jfieqnencies is shown in (B). Band-filtering noise reduction was utilized to increase data clari^ without sacrificmg low-frequency information. This is demonstrated by the arrow in both graphs, where a small microsaccadic overshoot is only clearly seen after noise reduction. 129 y 40 0 20 1 ° 2 -20 I -40 -60 -80 -100 0 1 2 O z 1 0 I -20 I -40 I -60 -80 -100 0 1 2 TIM E (SECONDS) FIGURE 4.9: Example of eye position data before noise correction is shown in (A). The same data after band-lSltering of the two dominant noise firequencies is shown in (B). This example demonstrates increased clari^ of end-gaze nystagmus via noise filtering without sacrificing true low-firequency information. The fast phase components of nystagmus are seen as the sharply downward sloped eye position lines, such as those highlighted by the arrows. 130 -20 -40 -60 -80 -100 0 1 2 Tim e (seconds ) FIGURE 4.10: Example of discarded subject eye position data. These data are typical of three subjects where electrical noise occurred. 131 80 " ' 60 - I 4 0 - 0 20 - 1 0 - - 2 -20 - % o ^ 0 - - fid M -60 - -80 - 0 0 1 0 2 0-1 30 40 50 E y e Ro t a t io n A n g l e (d eg rees ) FIGURE 4.11: Overall fixation positions while subjects viewed the 0“ target with head and eye straight-ahead. Individual subject components of these data are relative to the respective subject's mean fixation position measured while the head and eye were straight-ahead. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with, error bars. Positive values indicate gaze undershoots. 132 < Cl. o 5 ë 0 1 >Cd Cd 0 10 20 30 40 E ye R o t a t io n a n g l e (d eg r ees ) FIGURE 4.12: Before correctîoa for scierai search coil slippage: overall fîxation positions without the use of an afterimage while the subjects viewed the 0 ° target during each nasal eye rotation angle. Individual subject components of these data are relative to the respective subjects mean fîxation position measured while the h ^ and eye were straight-ahead. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with error bars. Positive values indicate gaze undershoots. 133 < u. o 5 2 z 0 E 1 fid > Ed -100 - E y e R o t a t io n A n g l e (degrees ) FIGURE 4.13; Before correctîoa for scierai search coil slippage: overall fixation positions with the use of an afierim%e while the subjects viewed the O*’ target during each nasal eye rotation angle. Individual subject components of these data are relative to the respective subject's mean Station position measured while the head and eye were straight-ahead. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with error bars. Positive values mdicate gaze undershoots. 134 < 0 z BBH 1 J B 9 B L 0 1 Ed -100 - 0 10 20 30 40 Eye Ro ta tion Angle (degrees ) FIGURE 4.14; Overall Sxatioa positions without the use of an afterimage while the subjects viewed the 0 ° target during each nasal eye rotation angle, hidividual subject components of these data are relative to the respective subject's mean fîxation position measured while the head and eye were straight-ahead. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with error bars. Positive values mdicate gaze undershoots. 135 < u. o S s 0 1H bd W -100 - 10 20 30 E y e R o t a t io n A n g l e (degrees ) FIGURE 4.15; Overall fîxation positions with the use of an afterimage while the subjects viewed the 0° target during each nasal eye rotation angle. Individual subject components of these data are relative to the respective subject's mean fîxation position measured while the head and eye were straight-ahead. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with error bars. Positive values indicate gaze undershoots. 136 Subject 2 • 1 ( 0 45 ■ 2 35 ♦ 3 I ^ 4 Ç 25 a 5 & a 6 B o 15 * 7 w 5 £ 5 c 15 1 0 2 0 30 40 Eye Rotation Angle (degrees) FIGURE 4,16; Interactioii plot of (subject x eye rotation angle). 137 Subject 2 • 1 es 25 ■ 2 *5 ♦ 3 A. 4 I 15 5 a 6 *. c * 7 0 5 5 1 5 c ( 0 -15 0 1 Presence/Absence of Afterimage FIGURE 4.17: Interactioii plot of (subject x presence/absence of afterimage). 138 Angle 2 ( 0 2 0 • 1 0 ■ 2 0 ♦ 30 Ic ‘ 40 t 1 0 § s l 0 C ( 0 0 1 Presence/Absence of Afterimage FIGURE 4.18: ùiteraction plot of (angle x presence/absence of afterimage). 139 < 0 40 z 1 z 2 t % £ -20 k u H -40 - z U -60 — S -80 - -100 0 1 0 2 0 30 40 EYE R o t a t io n a n g l e (d eg r ees ) FIGURE 4.19: Mean eye positions for individual subjects during each nasal eye rotation angle. The best-fit non-linear regression line is also shown. 140 < 40 o 5 ë 0 -20 1u -40 -60 -80 -100 0.0 0.5 1.0 1.5 2.0 T im e (SECONDS) FIGURE 4J&Q: Eye position relative to the target center for Subject 4 while fixating straight-ahead These data illustrate the typical appearance of two m icro-^e movements, microsaccades and slow drifts. A microsaccade, indicated by an arrow, moves the eye right by approximately 18 minutes of arc. A small corrective movement occurs, to place the eye approximately 10 minutes of arc right of the target Slow left then right ocular drift is apparent finm 0.75 seconds to the end of the data collection. 141 60 50 a ë 40 2 2 -} 30 0 1 3 2 0 a 1 0 0 0 1 0 2 0 30 40 E y e R o t a t io n a n g l e (d eg r ees ) FIGURE 4.21: Mean microsaccadic duration during each nasal eye rotation angle. Circles represent data collected without the presence of an afterhnage, while triangles represent data collected during the presence of an afterimage. Error bars = ± I standard deviation. 142 60 50 'à < o 40 5 S Cd a 30 3 j 0 . S 20 < 10 0 0 10 20 30 40 E ye R o t a t io n a n g l e (d eg rees ) FIGURE 4.22: Mean microsaccadic amplitude during each nasal eye rotation angle. Circles represent data collected without the presence of an afterimage, while triangles represent data collected during the presence o f an afterimage. Error bars = ± I standard deviation. 143 û c/3I I S û > t § U > < fà eu 10 20 30 40 E y e R o t a t io n a n g l e (degrees ) FIGURE 4.23: Mean microsaccadic peak velocity during each nasal eye rotation angle. Circles represent data collected without the presence of an afterimage, while triangles represent data collected during the presence of an afterimage. Error barsI standard deviation. 144 1000 • I. û * gI 100 I I § Cd > < fà Pm 101 100 1000 AMPLITUDE (MIN OF ARC) FIGURE 4.24: Main sequence plot of microsaccade data firom this dissertation research, along with Zuber and Stark microsaccade and saccade data.^^ Squares represent Zuber and Stark microsaccadic data, cross-hairs represent microsaccadic data firom this dissertation research and circles represent Zuber and Stadc saccade data. The peak veloci^ of the eye movement is shown as a function o f its amplitude. 145 40 I I 30 f 20 u X % o u os 3 10 < u S 0 0 10 20 30 40 I d e a l S e a r c h C o il P o s it io n (degrees ) FIGURE 4.25: Relationship of ideal search coil position to measured search coil position for three calibration techniques. Squares: produced by a mechanical device specifically designed for scleral s ^ c h coil equipmenL This is considered the gold standard calibration. Triangles: produced while the subject's head was rotated into temporal angles, but the eye remained in primary gaze. Circles: produced while the subject's eye rotated into temporal angles, but the head was fixed straight-ahead. 146 < U. 0 5 S Ed U Z Ed 1 Z < Ed 10 20 30 40 T a rg et Po sitio n (degrees ) FIGURE 4.26: Mean differences between two human calibration techniques. This data effectively describes the e& cts of search coil slippage and subject eccentric fixation at each target angle. The median, 10th, 25th, 75th and 90th percentiles are represented by boxes with error bars. Positive coil position values indicate measured gaze undershoots. 147 CHAPTERS DISCUSSION 5.1 SCLERAL SEARCH COIL SLIPPAGE A goal of this dissertation was to measure and define scleral search coil slippage. To accomplish this, such things as the relationship between slippage amplitude and the angle of gaze, and the consistency of the slippage at a given angle will be described. In addition, the direct method of the author for detecting search coil slippage will be compared with the classic indirect method of Collewijn.** Quantification o f search coil slippage is necessary if search coils are to be used to determine whether subjects fixate inaccurately in extreme-gaze. 5.1.1 SLIPPAGE CHARACTERISTICS The data presented here show evidence of scleral search coH slippage during extreme nasal gazes. Scleral lens slippage was always in the temporal direction, possibly due to contact between the lens and the eyelids. Furthermore, scleral lens slippage progressively increased with the angle of eye rotation. Overall, mean lens slippage was 0.0,2.0,5.0,11.9 and 23.3 minutes o f arc for nasal eye rotations o f 0°, 10°, 20°, 30° and 40°, respectively (Table 4.1). Significant search coil slippage occurred in the sample while subjects fixated nasally 30° and 40° (Table 4.4). Search coH slippage varied between individual subjects. Some subjects showed more overall search coil slippage, and some subjects had larger unit increases in search coil slippage as the angle o f qre rotation increased. However, the standard deviations fi)r slippage were small for all subjects at each eye rotation angle (Table 4.1). This suggests that for each 148 individual, the scleral search coil repeatedly slipped to a specific position during each eye rotation. The scleral lens then returned to its original position once the eye returned to primary gaze. 5.1.2 SLIPPAGE THEORY After producing the only experimental evidence of scleral search coil slippage. Van Rijn et al. theorized about the cause of the slippage.-" They speculated that slippage could occur for one of the following reasons. First, the coil may rotate relative to the bulbar conjunctiva. Second, the bulbar conjunctiva may concurrently rotate with the coil, with both returning to their original position via elastic restoring forces, hi the dissertation experiment, the position of the underlying bulbar conjunctiva during eye rotations was not monitored. However the characteristics of scleral lens slippage obtained in this experiment can still allow evaluation of Van Rijn’s theories. The first theory ofVan Rijn proposed that the coil rotates atop the bulbar conjimctiva. In determining if this were the reason for search coil slippage, one might assume that the eyelids provide the force necessary to overcome the static friction between the scleral lens and the bulbar conjimctiva. Once this friction is overcome during an eye movement, the lens could slide along the conjunctival surface. At the completion of the eye movement, the scleral lens would stabilize at its new position. As the eye returned to its original position, the scleral lens could also return to its original position, but only if the eyelids provided exactly the right force to the lens. This seems improbable, as the lens is likely to come to rest at (hfforent positions along the surface of the uneven conjunctival surface. To determine the consistency of the scleral lens slippage at each angle of eye rotation, one can look at the standard deviations of scleral lens position over the range of eye rotation angles (Table 4.1). fr^the scleral lens slides atop the bulbar conjunctiva with eccentric eye rotations, then these standard deviations are likely to be large. On the contrary, the standard deviations o f scleral lens slippage were small for individual subjects; eigh^-nine percent of all values were less than 6.0 minutes o f arc. Furthermore according to this theory, sliding the scleral lens atop the bulbar conjunctiva with gentle foiger pressure should have been possible, but this could not 149 be done. These results oppose the first theory of Van Rijn, and suggest that search coil slippage was under the control of something in addition to the eyelids. The second theory of Van Rijn proposed that the bulbar conjimctiva and the scleral lens slide together with eye rotations into eccentric gaze. Movement of the bulbar conjunctival overlying the sclera is easily demonstrated with gentle finger pressure. At an eccentric position, eyelid pressure would provide enough force to hold the scleral lens/conjunctiva in the “slipped” position. During the return eye movement, the scleral lens and conjunctiva would progressively return as a unit to their original positions via elastic restoring forces within the bulbar conjunctiva. This arrangement is analogous to a dish of gelatin dessert: as a force parallel to the dish is applied to the gelatin top, the dessert deflects an amount proportionate to the force. When the force is removed, the gelatin returns to its original position by internal elasticity. Sliding of the bulbar conjunctiva and scleral lens explains the data collected in this dissertation best Consistent elastic forces within the bulbar conjunctiva could have resulted in the low variability in search coil slippage with eye rotations in individuals. It is concluded that the scleral lens and bulbar conjunctiva most likely slid together during eccentric eye rotations, then returned to their original positions in primary gaze. The next section discusses two methods for detecting scleral search coil slippage. This information further supports the second theory o f Van Rijn. 5.1 J METHODS FOR DETECTING SLIPPAGE One strategy is commonly used during scleral search coil studies to assess stability of the scleral lens on the eye. This is the indirect method popularized by Collewijn et a i, where variability in the recordings describing the eye’s position is monitored.** It is thought that search coil slippage should be revealed by inconsistencies between data describing a subject’s fixation (and therefere the search coil’s position) in primary gaze before and after large saccadic eye movements.’’***'’®^ ff^no significant difference is found between the two data sets, the scleral lens is assumed to be firmly adhered to the conjunctiva. If a significant difierence is found, it must be assumed that (I) the scleral lens slipped atop the bulbar 150 conjunctiva during the eye rotation, and (2) the lens did not return exactly to its original position once the eye returned to primary gaze. Overall, significant search coil slippage has never been found using this technique.®’^*’®*’® In this dissertation research, a direct method for measuring scleral lens slippage was utilized. High-magnification photographs were taken of the scleral lens while the subject fixated a single target in multiple nasal gazes (three times randomly over angles of 0°, 10°, 20°, 30° and 40°). Thus the position of the search coil was determined at eye positions other than primary gaze. Since the indirect method of Collewijn is concerned only with primary gaze data, it may fail to detect scleral lens slippage during eccentric gazes that the direct method could successfully identify. The inverse is not true. The direct method can also detect any scleral search coil slippage identified by Collewijn’s indirect method. It too examines for inconsistencies in the search coil position during primary gaze before and after saccadic eye movements. This dissertation research has concluded that scleral search coil slippage can occur during extreme lateral gazes. In addition, for each subject at each eye rotation angle, the standard deviation of lens position was fypically small. Therefore the scleral lens repeatedly slipped to a specific position for each nasal eye rotation, and then repeatedly slipped back to its original position as the eye returned to primary gaze. This result supports the idea that the scleral lens and conjunctiva both slide during eye movement. The overall search coil position mean durmg primary gaze was 0 minutes of arc, with a standard deviation of 4.2 minutes of arc (Table 4.1 and Figure 42). In addition, the overall fixation position mean during primary gaze was 0 minutes of arc, with a standard deviation of 4.6 minutes of arc. (Table 4.5). The indhect method of Collewijn would have failed to detect scleral search coil slippage based on primary gaze data fiom this research. 151 5^ OCULAR FIXATION IN ECCENTRIC GAZE The primary goal of this dissertation research was to quantify and analyze the accuracy and precision of extreme-gaze ocular fixation. This was possible after the confounding influence of scleral search coil slippage was removed ftom subjects’ eye position data. This section describes the mean and standard deviation of fixation during primary gaze and at multiple nasal eye rotations. The concept of conjugate stress-induced eccentric fixation is analyzed, and a theory that describes fixation in extreme angles of gaze is proposed. A secondary goal of this dissertation research was to examine characteristics o f the eye movements occurring during ocular fixation in extreme gaze. This section describes the mean duration, amplitude and peak velocity o f microsaccades over a the range of eye rotation angles. Main sequence microsaccadic data fiom this dissertation research are also compared to the main sequence microsaccade and saccade data of Zuber and Stark and others. End-gaze nystagmus characteristics will also be described and compared with the results of previous studies. A unique end-gaze nystagmus case is discussed, along with a theoretical explanation. 52.1 ACCURACY AND PRECISION OF GAZE Ocular fixation studies have classically described the position of the eye in terms of its mean and standard deviation.®'^*’*^ ** This dissertation research relied upon the same approach. Eye position data collected during primary gaze were normally distributed, with an overall mean of 0 minutes of arc and a standard deviation of 4.6 minutes of arc (Table 4.5). This standard deviation was within the typical range (~2-7 minutes of arc) found in previous studies.*"*”'’® Outside of primary gaze, mean eye positions became progressively more inaccurate during fixation of a target over ascending nasal gaze angles. When subjects were permitted to view the target normally (/.e., without an afterimage), overall fixation was nearly exact for 10°, 20“ and 30“ nasal eye rotations. For these gazes, overall mean eye positions lagged the target center by only 2.4, 5.6 and 4.3 minutes of arc, respectively (Table 4.8). These correspond to accuracies (r.e., [true eye rotation/ tye rotation demand] x 100%) o f99.6,99.5 and 99.8%, respectively. Such accurate 152 fixation demonstrates the remarkable ability of the central nervous system to control fixation. During 40“ nasal eye rotations, the overall mean eye position was less accurate. Here the eye lagged the target center by 14.5 minutes o f arc (Table 4.8). However this still produced an accuracy of 99.4%. Standard deviations of fixation position for individuals did not appear to change significantly over eye rotation angles, and most were less than 7.0 minutes of arc (Table 4.8). These results were similar to those published by Ferman et al. (Section 2.2.4).’ That experiment was run under conditions similar to those of this dissertation research. The eye’s position was monitored with scleral search coil equipment, and under monocular conditions, subjects fixated a target during static lateral head rotations of ±15“. While fixation accuracy was approximately 100% for four of the eight subjects at this eye rotations of 15“, accuracy for the remaining was worse than 99.9% ^9 minutes o f arc lag). Two subjects produced accuracies of 97.8% and 972% {Le., 20 and 25 minutes of arc lag, respectively). It should be noted that these accuracies may be artificially low: this Ferman experiment did not correct for scleral search coil slippage. During the dissertation research when subjects fixated the target with a foveal afterimage, overall fixation was accurate for 10“ and 20“ nasal eye rotations. For 10“ nasal gazes, the overall mean eye position overshot the target center by 6.1 minutes o f arc. For 20“ nasal gazes, the overall mean eye position lagged the target center by only 0.9 minutes of arc. During 30“ and 40“ nasal gazes, fixation was less accurate. Here the overall mean eye positions lagged the target center by 122 and 19.1 minutes o f arc, respectively. However this still produced accuracies of 99 J and 99.2%, respectively. Again, fixation standard deviations for individuals did not appear to change significantly over eye rotation angles, and most were less than 7.0 minutes of arc. Statistically, eye position was analyzed as a ftmction of subject (p < 0.005) and eye rotation angle (p < 0.0005). Affirming past Ferman’ data, this result indicated that fixation became more inaccurate with gaze eccentricity, and that some subjects showed larger fixation inaccuracies than others. Overall, only the mean focation position measured at 40“ was significantly difforent firom that measured durmg primary gaze. 153 522 GAZE ACCURACY THEORY It was hypothesized in the hitroductioa chapter that in extreme gaze, the eye may be under conjugate stress in its attempt to maintain fixation. This could cause a perceptual adaptation in which the person believes the eye is rotated to a greater extent than it actually is. A different point on the retina would come to represent the visual direction formerly represented by the fovea, a condition frequently called eccentric fixation.' Two requirements must be met in the dissertation to establish the presence of conjugate stress-induced eccentric fixation. First, overall mean eye positions must have significantly lagged that of the visual target This was the case, at least for eye positions measured during 40° eye rotations. Second, a significant difference must have been found between the mean eye positions in the without and with afrerimage conditions. It was proposed that the afterimage condition would “force” the subject’s fovea on target and eliminate eccentric fixation, while the without afterimage condition would permit eccentric fixation to occur naturally. A significant difference between the eye positions under the two conditions would gauge the magnitude of eccentric fixation. However, no eccentric fixation was detected in the dissertation data: the presence of an afterimage did not significantly influence the accuracy of ocular position (p = 0.956). It is assumed that subjects used the fovea to fixate the visual target under both conditions. Since both requirements were not met, conjugate stress-induced eccentric fixation did not occur. However one problem remained. Even when scleral lens slippage was accounted for, the data indicated that the scleral search coil (and therefore the anterior surface of the eye) significantly lagged the visual target during 40° eye rotations. Yet concurrently, subjects were fixating the target with their fovea. This suggests that during extreme angles of gaze, the anterior globe did not accurately represent the position of the fovea. Three potential situations could allow for proper foveal fixation while also inducing an apparent ocular lag in the scleral search coil data; foveal shifting, lateral translation of the globe or tilt of the crystalline lens. The idea that at extreme angles of gaze, retinal stretchmg or crystalline lens displacement could affect the paceptual localization o f the fovea was introduced m the 154 Historical Review chapter and was termed “optical sliding (Section 2.4). Before the theoretical basis of the three potential explanations are offered, the “normal" path of the ocular line of sight (LOS) through the Gullstrand Simplified Schematic Eye (Schematic Eye) will be explained. The remainder of this section will use the distances and refiactive indices of the Schematic Eye listed in Table 5.1 in its calculations. Angles A, B and D represent the angles between the LOS and the optic axis at the plane of the entrance pupil, the true pupil and exit pupü, respectively. Angle C represents the angle between the LOS and the optic axis after refraction by the anterior lens surface. All relevant angles, distances, refractive indices and calculations will be highlighted in figures listed below. The LOS travels from the visual target to the center of the eye’s entrance pupil.' During primary gaze, the LOS produces an angle of ^roxim ately 1.5° with the ocular optic axis at the entrance pupil plane {Le., Angle A).^ Once the LOS strikes the anterior comeal surface, its course is refracted so that the LOS travels to the center of the true pupil {Le., Angle B). Figure 5.1(A) illustrates and calculates the path of the LOS through the cornea of the Schematic Eye. Figure 5.1(B) illustrates and calculates by Snell’s Law, the path of the LOS through the anterior crystalline lens surface {Le., Angle C). Once the LOS strikes the posterior lens surface, its course is refracted so that the LOS travels from the center of the exit pupil to the fovea {Le., Angle D). Given that Angle D is calculated as 1.23“, and the distance between the retina and «dt pupil plane is approximately 20.26 millimeters, the fovea is positioned about 0.44 millimeters temporal to the optic axis in the Simplified Eye. Figure 5.1(C) illustrates and calculates the path of the LOS from the posterior lens surface to the fovea. Foveal shifting is one situation that would allow proper foveal fixation while also inducing an apparent ocular lag. It is conceivable that during extreme rotations of the eye, force is transferred from the contracting extra-ocular muscle to the globe itself. ^ large enough, this force could potentially buckle the retina and shift the position of the ft)vea relative to the anterior globe surface. Retinal shifts have been reported before, but only as a result of accommodation. It has been shown that marked accommodation can produce a 155 distortion in monocular space perception in the horizontal meridian, with the effect due largely to retinal shifting ” Here, contraction of the ciliary body causes the ora serrata to extend anteriorly 0.5 millimeters.” ’ “ Retinal shifting can also occur in the posterior pole. Hollins has shown that during 9 diopters o f accommodation, the central region o f the human retina can shift approximately 20 minutes of arc.** Figure 5.2 calculates the foveal shift necessary to induce an apparent ocular lag of 14.5 minutes of arc. This amount of ocular lag was chosen since it was the overall mean eye position lag found during a 40“ eye rotation without the use of an afterimage (Table 4.8). Assuming foveal fixation remains accurate and the target remains stable. Angle A must change with a foveal shift Figure 52 shows that based on an anterior ocular surface lag of 14.5 minutes of arc, the resultant Angle A is approximately 1.503“ during 40“ eye rotations. From this. Angles B, C and D are calculated as 1.48“, 1.40“ and 1.43“, respectively. Angle D is used to calculate the new foveal position as 0.51 millimeters temporal to the optic axis. Since the original position of the fovea was calculated to be 0.44 millimeters temporal to the optic axis (Figure 5.1(C)), the fovea has shifted temporally by approximately 0.07-0.08 millimeters. Based on previous research, this level of foveal shift is possible. Nasal translation of the right eye during eye rotations is another situation that would allow proper foveal fixation while also inducing an apparent ocular lag. This is possible for two reasons. First, the insertion of the medial rectus muscle into the globe is temporal to its origin at the Annulus of Zinn.^^ Second, a relatively large force is required of the medial rectus to overcome elastic restoring forces and rotate the eye into extreme nasal gaze. Considering the muscle-globe geometry and increased force demands during extreme globe adductions, it is possible that a medial rectus contraction could induce a nasal eye translation. However, this theory is not supported in literature. While measuring the center of ocular rotation. Fry and Hill used a large range o f lateral eye rotation angles, including ± 40“, and found no evidence of translation.^ Enright, on the other hand, found that the globe can displace within the orbit by 02 millimeters during strong convergence.^^ However, this displacement was in the temporal direction, not in the nasal direction required to induce an apparent ocular lag. 156 Nevertheless, Figure 53 calculates the nasal globe translatioa necessary to induce an apparent ocular lag of 14.5 minutes of arc. With a stable foveal position on the retina. Angle A must be 1.50“c^er the globe translation for proper foveal fixation (Figure 5.1(A)). If the eye is translated nasally. Angle A is altered firom 1.50° to a smaller amount To produce an Angle A of 1.50°, the eye must then rotate in the temporal direction. This new eye position would appear as an ocular lag to the scleral search coil equipment As illustrated in Figure 5.3, the right eye must translate nasally approximately 4 millimeters to induce an apparent ocular lag of 14.5 minutes of arc. Considering that the eye is thought to translate only fractions of a millimeter or not at all, 4 millimeters of ocular translation during extreme eye rotations seems unlikely. In addition, the design of the bite bar and pinhole used in the experiment prohibited eye translations of this size (Section 333). During the with afterimage condition, this dissertation research placed a pinhole (subtending approximately 10 minutes of arc) 50 centimeters from the subject It rested directly between the eye and the 0“ LED target (which subtended a visual angle of 6 minutes of arc at its 1 meter test distance). Since subjects were required to have the full target in view through the pinhole during data collection, equipment geometry permitted less than 1 millimeter of lateral globe translation. Considermg the success of subjects in viewing the frill target through the pinhole during extreme eye rotations, this dissertation suggests that the line of sight truly rotated about an approximate, single center of eye rotation. Crystalline lens tilt during eye rotations is a third situation that would allow proper foveal fixation while also inducing an apparent ocular lag. It is conceivable that during extreme rotations of the eye, force is transforred from the contracting medial rectus muscle to the globe itself. If large enough, this force could potentially rotate the position of the crystalline lens withm the globe. A compensating eye rotation would be required to correct for this lens tilt and allow for proper foveal fixation. Figure 5.4 calculates the crystalline lens rotation necessary to induce an apparent ocular lag of 14.5 minutes of arc. To minunize complicity, it is assumed that the lens rotates about its anterior pole at the optic axis, and that the location of the exit pupü center does not significantly change with small lens rotations. A lens tüt would requfre an adjustment in the 157 size of Angle A, so that the LOS can travel finm the stable visual target, refract though the altered lens and still fall on the stable fovea. All four angles are known: Angles A and B are 1.74“ and 1.48“, respectively, when the globe lags the target by 14.5 minutes of arc (Figure 52). Angle D is the angle between the LOS and the optic axis at the plane of the exit pupil. Since the fovea and exit pupil center are fixed, this angle is 1.23“ (Figure 5.1(C)). Angle D can be used to calculate Angle C (r.e., [tan(Angle C) = (3.52 * tan(Angle D)) / 3.60] ). As shown in Figure 5.1(C), Angle C is 120“. Figure 5.4 illustrates Angle Delta, the angle separating the optic axis and the lens optical axis after a lens rotation. Using Snell’s Law and the known magnitudes of Angles B and C, Angle Delta is calculated as 3.56“ (r.e., [(1.336 * sin(1.478“ + Angle Delta)) = (1.413 * sin(l .203“ + Angle Delta))] ). Therefore, the optical axis of the crystalline lens must tilt approximately 3.6“ to induce an apparent ocular lag of 14.5 minutes o f arc. The temporal side of the lens rotates in a posterior direction, and the nasal side of the lens rotates in an anterior direction. To the knowledge o f this author, no research has studied dynamic crystalline lens tilt. Literature studying static lens tilt have been concerned only with measuring posterior chamber intraocular lens decentration and tilt following cataract surgery.’*^ Therefore the explanation to follow is purely theoretical. It may be possible for the crystalline lens to tilt 3.6“ during extreme eye rotations. However, the direction of tilt calculated in Figure 5.4 seems opposite to what would be expected. Upon contraction of the medial rectus, force could be transferred fiom the muscle to the crystalline lens. This force would tug the nasal side o f the crystalline lens back in a posterior direction. The calculations in Figure 5.4, rather, predict that the nasal side of the crystalline lens would move in an anterior directiotL Admittedly this is a simplistic view; additional research is necessary to investigate the true interactions of the extra-ocular muscles and the crystalline lens. Data finm this dissertation indicated that the position of the fovea was not perfoctly represented by the position o f the anterior globe during 40“ adductions, h i this angle o f gaze, contradictory information was collected: the scleral search coH equipment indicated that the globe lagged the visual target, Wnle concurrently the afterimage technique suggested proper 158 fbveal fixation. Of the three suggested situations that could allow for foveal fixation while also inducing an apparent ocular lag, fbveal shifting is the most plausible. Only -0.08 millimeters of shift is necessary to induce a 14.5 minute of arc ocular lag. Accommodation research has shown that the retina at the posterior pole can shift the necessary amount to accomplish this. Another situation, crystalline lens tilting, could also allow foveal fixation but produce an apparent ocular lag. Unfortunately no research has studied this question of dynamic lens tilt. However it is possible that the lens could tilt 3.6“ during extreme eye rotations to induce a 14.5 minute of arc ocular lag. The third situation, translation of the globe, does not seem probable. The eye would have to translate nasally 4 millimeters to induce a 14.5 minute of arc ocular lag. First, the research equipment geometry could not have permitted globe translations of this magnitude. And, translations of this size could not have escaped detection during past studies, especially in center of eye rotation research. 5J23 MICROSACCADE CHARACTERISTICS Microsaccades occurred during fixation in all seven subjects. Over the range of nasal eye rotation angles (f.e., 0“, 10“, 20“, 30“ and 40“), mean microsaccadic durations fell between 14.0 and 19.1 milliseconds (Tables 4.13-4.21). This compares favorably to reports that microsaccades typically occur in under 25 milliseconds.^'""'"" Mean amplitudes fell between 12.9 and 21J minutes of arc (Tables 4.13-4.21). Again this is comparable to other studies, where typical microsaccades have been found to have amplitudes under 25-30 minutes of arc wioo pcaij velocities fell between 23.6 and 34.8 degrees/second (Tables 4.13-421). This range of velocities is slightly higher than estimations found in eye movement literature. Microsaccade peak velocities Qfpically range firom 1 to 20 degrees/second.^^ There are two potential explanations ferthe higher-than-expected microsaccade mean peak velociti^ found in the dissertation research. First, microsaccades were identified based on a minimum peak velocity of 12.0 degrees/second. Setting such a high velocity criterion was required because of electrical noise within the subject data; the incidence of false- positive identifications was greatly increased with any reduction in this minimum peak velocity threshold. With less equipment noise, this minimum peak velocity criterion could 159 have been lowered, and more slower-velocity microsaccades may have been identified. Consequently the mean peak velocities for microsaccades may have dropped significantly. A second explanation for higher-than-expected microsaccade mean peak velocities, was that some of the microsaccades were actually voluntary saccades. This could be due to the upper-limit criterion of 50 minutes of. arc amplitude used for identification of microsaccades. By eye movement literature standards, this threshold was slightly high (see above). Based on main sequence plots, the presence of saccades would have elevated the mean peak velocities measured in the dissertation research. However without a method to monitor for the voluntary or involuntary nature of recorded eye movements, this dissertation assumed that eye movements which fit the main sequence plot of saccades/microsaccades were microsaccades unless clearly falling inside the characteristics of a saccade. The argument for this was that since subjects were exposed to only one visual target within a dark environment, there was no stimulus for voluntary saccades. Furthermore, there is a no clear division between microsaccades and saccades by amplitude or peak velocity. For example, Haddad and Steinman have shown that subjects can make volimtary saccades as small as typical microsaccades.’* Other researchers have reported that the amplitude of a microsaccade can be as large as typical volimtary saccades (r.e., ^50 minutes of arc).'°^ In general, eye movements are classffîed as either a microsaccade or saccade based on arbitrary, albeit educated, guesses. Certainly this is an area open for additional research. Nevertheless, data from this dissertation clearly bridged the gap between the microsaccade and saccade data of Zuber and Stark and others.^^ Figure 4 2 4 plots the main sequence of the dissertation’s peak velocity data as a frmction of their respective amplitude. Alongside is plotted Zuber and Stark’s main sequences of microsaccades and saccades. A continuous curve can be envisioned linking the three data sets. This supports the hypothesis that saccades and microsaccades are controlled by a single physiological system.^ All three microsaccade characteristics, duration, amplitude and peak velocity, varied by subject (p < 0.0005 for each). Both amplitude and peak velocity varied with angle of eye rotation, but with p values o f0.044and 0.049, respectively, this association was questionable 160 at best. The presence of afterimages did not significantly affect any characteristic of the microsaccades. This dissertation research provided microsaccadic data detailing duration, amplitude and peak velocity. These data were similar to those found in previous microsaccade studies, except for a slightly high mean peak velocity finding. This was thought due to the inability of the search coil equipment to clearly identify slow-velocity microsaccades, and/or the presence of voluntary saccades in the data. Nevertheless, main sequence plots detailing microsaccade data of this dissertation research fit neatly within the main sequence plots of previous microsaccade and saccade research. This suggests a single physiological oculomotor control system for both microsaccades and saccades. Microsaccade duration, amplitude and peak velocity varied by subject The presence of afterimages was not found a significant influence on these characteristics. Both amplitude and peak velocity varied by angle of eye rotation. However, with p values close to 0.05 in both cases, this association was questionable; additional research is necessary before conclusions can be formed. 52A END-GAZE NYSTAGMUS CHARACTERISTICS End-gaze nystagmus occurred in two of the seven subjects, and only during 40“ eye rotations. All cases fit typical jerk nystagmus criteria: amplitudes were between 025 and 5 degrees, fiequencies between 1 and 5 Hz and peak velocities were s 100 degrees/second.* ” '** The duration, amplitude and peak velocity for fast phase components (Table 4.25) were similar to corresponding descriptions of microsaccades (Tables 4.13-21) and saccades.^*^*^ This was an expected result since the fost phase component of jerk nystagmus is considered a rapid saccadic eye movement.* End-gaze nystagmus is thought due to a “leaky” velocity-to-posMon neural integrator (Section 2.2.3).* ' ^ As a subject fixates eccentrically, the “lealty” neural integrator causes the eye-position command to gradually reduce. Concurrently, the eye begins to drift back toward primary gaze. This slow eye deviation (the slow phase of nystagmus) stimulates a corrective saccade in the opposite direction (the fost phase of nystagmus). This theory was supported in most cases by the end-gaze nystagmus occurring m this dissertation research. 161 Always, the fast phase component of the nystagmus attempted to move the fovea closer to the target However, one example showed an. unexpected pattern. Trial A of Gaze Plot 32 shows the eye position data collected from Subject 4 while fixating during a 40“ nasal eye rotation. At approximately 0.35 seconds, a slow phase of jerk nystagmus drifted the right eye temporally. This moved the eye away from the target and toward primary gaze. At 0.45 seconds, a fast phase corrective movement initiated, and moved the eye back toward the target and away from primary gaze. These steps were expected, based on the “leaky” neural integrator theory mentioned above: the slow phase drift moved the eye away from the target and toward primary gaze, while the fast phase component returned the eye to the target and away from primary gaze. As approximately 0.55 seconds, a slow phase drift took the eye away from the target and away finm primary gaze. Fast phase corrective nystagmus occurred at 0.73 seconds, and moved the eye back toward the target and primary gaze. This pattern was then repeated. This example was the opposite of expected: the slow phase of nystagmus took the eye away from primary gaze, while the fast phase moved the eye toward primary gaze. To the knowledge of this author, this unusual occurrence has never been reported in nystagmus literature.*' This may be a case where the cerebellum provided excess input to the neural integrator. It is theorized that the cerebellum works through a positive feedback mechanism to adjust the “leaky” neural integrator’s time constant of decay.® The cerebellum increases the time constant to reduce slow drift of the eyes away fiom the visual target and toward primary gaze. If excessive innervation were provided by the cerebellum to the neural integrator, it is possible that the eye could actually begin a slow drift in the opposite direction, away from the visual target and primary gaze. Displacement of the visual target would then induce a corrective saccade, which would move the eye back toward the target and primary gaze. This scenario exactly describes the odd end-gaze nystagmus example outlined above. Unfortunately this imusual end-gaze nystagmus «cample only occurred in one subject during one 2-second data collection. Additional research is required to properly investigate this finding. 162 This dissertatîoa research provided end-gaze nystagmus data detailing the duration, amplitude and peak velocity o f fast phase components. Ail characteristics of these data were similar to those found in previous nystagmus studies, except for the direction of slow and fast phases in one case. A theory was provided that explained this phenomenon by excessive cerebellar innervation to the nemal integrator. Unfortunately end-gaze nystagmus occurred in only two subjects, and only during eye rotations of 40“. No formal statistical analyses were performed on the nystagmus data. 53 HUMAN CALIBRATIONS IN SCLERAL SEARCH COIL RESEARCH A goal of this dissertation was to determine the feasibility of using subjects to calibrate the scleral search coil equipment rather than using a mechanical device specifically designed for the task. The dissertation research was calibrated with a special search coil permanently fixed within a solid protractor unit. This mechanical device was rotated to preselected horizontal angles (/.e., -10“, 0“, 10“, 20“, 30“, 40“ and 50“) about a center of rotation which coincided with the subject’s center of eye rotatioiL At each angle, the computer recorded data detailing the device’s position, and a simple linear regression line was produced for the plot of digital signal versus sine of the angle of rotation. The slope of this regression line was used to calculate the magnitude of eye rotations for all subjects run during that particular day. Even though this calibration method relied on the ability of the experimenter to precisely position the calibration device at each rotation angle, all calibration regression lines of this dissertation research produced correlation coefficients of 1.0. For comparison, similar calibration data was collected fiom the subjects themselves. Scleral search coil equipment was used to measure the position of the eye while the subject fixated mdividual LED targets during temporal eye rotations (r.e., 10“, 20“, 30“, 40“ and 50“) while the head was foced straight-ahead. During this condition, the factors that influenced subjects’ fixational position were: improper LED ta%et positioning, search cod slippage (Section 5.1.1) and imperfect representation of the foveal position by the search coil 163 equipment during extreme angles of gaze (Section 522). As seen in Figure A29, calibration data firom this condition consistently lagged that of the mechanical device. Subject calibration data was also collected during primary gaze while the subject’s body was rotated into temporal angles {le., 10", 20", 30", 40" and 50"). Therefore the head and eye were always in the primary position. This eliminated the influences of search coil slippage and imperfect representation of the foveal position by the search coil equipment {Le., optical sliding or lateral ocular translation). Under this technique, the subject’s fixational position was influenced only by improper LED target positioning. As seen in Figure 429, calibration data firom this condition consistently lagged that of the mechanical device. However this lag was slightly less than the calibration data collected during temporal eye rotations while the head was fixed straight-ahead. The difference between these two conditions {Le., subject calibrations during primary gazes minus subject calibrations during temporal eye rotations) estimated the overall influence of scleral search coil slippage and/or the imperfect representation of the foveal position by the search coil equipment Therefore this suggests that during extreme temporal eye rotations, search coil slippage and/or imperfect representation of the fbveal position by the search coil equipment did occur. This also supports the result that these influences were present during extreme nasal eye rotations (Sections 5.1.1 and 5.22). Since the mechanical device calibration differed so greatly firom that of the human subjects in extreme positions, one might question the validity of relying on it to calibrate the dissertation research. After all, the primary goal of the dissertation was to describe the accuracy and precision of extreme-gaze fixation. This argument is dismissed when reminded that the subjects’ heads may have been rotated through angles of 0" to 40° during data collection, but the eye always attempted fixation on the same 0" LED target. The actual range of eye positions never passed outside of ±2" firom the target hi this confined range, the human and mechanical device calibrations were identical (Figure429). Outside of 10", this was not true. For search coil-based «rperhnents where the head is fixed straight-ahead but the eye is rotated into eccentric lateral angles greater than 10", it may be more accurate to calibrate 164 with hinnan subjects rather than the mechanical device. Eye rotations of at least 30° can be calibrated by fixing a subject’s head straight-ahead, and having them fixate individual LED targets in temporal gazes (e.g:, 0°, 10°, 20° and 30°). Since scleral search coil slippage during extreme nasal gazes was shown to be repeatable (Section 4.1.1), this calibration technique would eSectively eliminate the influence of search coil slippage firom research data. Since improper LED target positioning would be present during the subject calibration and experimental data, this confounding variable would be eliminated firom research data. And imperfect representation of the foveal position by the search coil equipment during extreme gazes would be present during the subject calibration and experimental data. Its influence would also be effoctively eliminated firom research data. This dissertation research conducted calibratioas using a mechanical device specifically designed to calibrate scleral search coil equipment. At extreme angles, the calibrations firom this mechanical device dififored firom calibrations collected firom subjects. However due to the study design, this factor did not adversely influence the data of the dissertation research. For search coil studies that require subjects to gaze into eccentric gazes > 10°, it was recommended that calibrations be performed by the subjects themselves. This would effectively eliminate the influences o f s^rch coil slippage, improper target positioning and imperfoct representation of the foveal position by the search coil equipment. However the range of human calibration angles should be minimized (e.g., g30°) to eliminate the presence of end-gaze nystagmus. 165 D is t a n c e F r o m C o r n e a l Po l e : 3:05 |mi!!imefeES> Pupil 3.60 Antenor&eniFSuE^eet Exit Pupil 3.68 FostenorLeiis SiiEâee 1 7.20 Retina 23.94 INDEX O f R e f r a c t io n : AqumugBumoF 1 1336 Crystalline Lens 1.413 Table 5,1: Relevant positions and refractive indices for the #2 Gullstiand Simplified Schematic Eye.” 166 3.60 mm 3.05 mm X X FIGURE S.lfAh Path of the ocular line of sight (LOS) through the Gullstrand Simplified Schematic Eye: Comeal refiaction. By definition, the LOS travels fiom the fixation target to the center of the eye^s entrance pupil. Angle A is created as the LOS intersects the optic axis at the entrance pupil; this angle is approximately 1.5°.** Comeal refiaction changes the LOS's path so that it intersects the optic axis at the center of the true pupil. Here, the two axes create Angle B. Given Angle A is 1.5°, the distance finm the comea to the entrance pupil is 3.05 mm and the distance fiom the comea to the trae pupil is 3.60 mm. Angle B is 12 T (f.e., [tan(Angle B) = (3.05 * tan(Angle A)) / 3.60] ). 167 B FIGURE Path of the ocular line of sight (LOS) through the Gullstrand Simplified Schematic Eye: Refiaction at the anterior lens. The deviation of the LOS through the anterior lens can be calculated with Snell’s Law: [(Aqueous,^ * sin(Angle B) = (Lensw _ Reftjeàon) * sin(Angle C)]. Given Angle B = 1 2 T , the aqueous index of refiaction = IJ36 and the lens index of refiaction = I.413, Angle C (the an^e between the LOS and optic axis at the anterior lens surface) is 1.20®. 168 C. 3 .5 2 mm 3.60 mm FIGURE 5.1(0; Path of the ocular line of sight (LOS) through the Gullstrand Simplified Schematic Eye: Refiaction at the posterior lens. Refiaction at the posterior surfice of the lens changes the LOS’s path so that it travels fiom the center of the exit pupil to the fovea. The intersection of the LOS and optic axis at the center of the exit pupil creates Angle D. Given Angle C is 12°, the distance fiom the anterior to the posterior lens surfaces is 3.60 mm and the distance fiom the exit pi^il to the posterior lens surface is 3.52 mm. Angle D is 123" {Le., [tan(Angle D) = (3.60 ♦ tan(AngIe Q ) / 3.52] ). Given the distance fi»m the exit pupil to the posterior ocular pole is 2026 and Angle D is 123°, the fovea is positioned 0.435 mm temporal to the posterior pole {Le., [tan(Angle D) = (fovea position) / (202QJ ). 169 25.87 mm P5.87 ♦ 0.05) mm target (987.92-0.0001) mm LOS 14.5 987.92 mm LOS Entrance Pupil COR FIGURE 5^: Approximately 0.08 millimeters of foveal shear is necessary to induce an apparent “fixation lag” of 14.5 minutes of arc. (A) schematically illustrates the ocular line of sight (LOS) as it passes firom the fixation target to the entrance pupil under normal conditions in the Gullstrand Simplified Schematic Eye. The target plane is -98.8 centimeters firom the ocular entrance pupil, and the target is -2.6 centimeters tangent to the optic axis (assuming Angle A is 1.5°). This schematic is identical to the example shown in Figure 5.1(A). ^ ) illustrates how Angle A changes when the globe lags the target by 14.5 minutes of arc. The new Angle A (r.e.. A’) is now (1.503° + 0242°) = 1.744°. By following the steps in Figure 5.1(A, B and C), the displaced position of the fovea can be calculated by using Angle A’ to calculate new Angle B [tan(Angle B) = (3.05 * tan(1.744°)) / 3.60], Angle B = 1.478°), by using new Angle B to calculate new Angle C (i.e., [sin(Angle C) = (1.336 * sin(l.478°)) / 1.413], Angle C = 1398°) and by using new Angle C to calculate new An^e D (f.e., [tan(Angle D) = (3.60 ♦ tan(1398°)) / 3.52], Angle D = 1.429°). The new position of the fovea is 0.51 millimeters temporal to the optic axis (f.e., [(tan(1.429°) * 2026) = x)]). Smce the original position of the fovea was calculated to be 0.435 millimeters temporal to the optic axis (Figure 5.1(C)), the foveal shear necessary to induce an apparent ‘N ation lag” of 14.5 minutes of arc would be approximately 0.08 millimeters in the temporal direction. 170 21.87 mm ^1.87 * 0.05) mm target (987.92 - 0.0001) mm y Optic Axis 1.267 degrees LOS ^ Optic Axis 987.92 mm LOS Entrance Pupil 11.75 COR FIGURE 53; The right eye must translate nasally approximately 4 millimeters to induce an apparent “fixation lag” of 14.5 minutes of arc. (A) schematically illustrates the ocular line of sight (LOS) as it passes firom the fixation target to the entrance pupil after a 4 millimeter nasal translation of the Gullstrand Simplified Schematic Eye (compare to Figure 52(A)). The target plane is -98.8 centimeters firom the ocular entrance pupil, and the target is -2 2 centimeters tangent to the optic axis. The creates an Angle A of 127°, which moves the target image off the fovea. (B) illustrates how the eye must rotate 14.5 minutes of arc to the right in order to produce a new Angle A of (1267 + 0242) = 1.5°. With an Angle A of 1.5“, foveal fixation is permitted (See Figure 5.1(A, B and C)). 171 Optic Axis □ ■ I Lens Optical Axis FIGURE 5.4; The crystalline lens must rotate approximately 3.6“ to induce an apparent “fixation la ^ o f 14.5 minutes of arc. (A) illustrates the ocular line of sight (LOS) as it passes through a Gullstrand Simplified Schematic Eye containing a rotated lens. Angles A and B are 1.744“ and 1.478“, respectively, when the globe lags the target by 14.5 minutes of arc (Figure 5.2). (B) illustrates the angles involved in the refiaction at the rotated anterior lens surface. Angle Delta is the angle between the optic and lens optical axes. LOS angles of incidence and emergence are calculated as (Angle B + Angle Delta) and (Angle C + Angle Delta), respectively, hi order for the LOS to intersect the fovea. Angle C must be 120“ (Figure 5.1(C)). Therefore lens rotation. Angle Delta, is calculated as 3.56“ by Snell's Law (î.e. [(1.336 * sin(1.478“ + Angle Delta)) = (1.413 * sm(1203“ + Angle Delta))]). 172 CHAPTER 6 CONCLUSION 6.1 OCULAR FIXATION IN ECCENTRIC GAZE Conjugate stress-induced eccentric fixation was not present in the dissertation data, since no difference was found between the fixation positions with and without a foveal afterimage. Yet concurrently, the scleral search coil measurements (corrected for slippage) indicated that the accuracy of fixation diminished as the gaze angle increased. The combination of these contradictory findings, that ocular fixation was inaccurate in extreme gazes but the fovea was being used for fixation, suggested that the position of the fovea was not perfectly represented by the position of the anterior globe (and therefore the scleral search coil). The theory o f‘"optical sliding” best explains this phenomenon: it seems possible that at extreme angles of gaze, retinal stretching/shifting or crystalline lens tilting could affect the perceptual localization of the fovea in visual space. Of the two “optical sliding situations that could allow for foveal fixation while also inducing an apparent fixation lag, foveal shifting is the most plausible. Only -0.08 millimeters of shift is necessary to induce a 14.5 minute o f arc fixation lag (the overall mean eye position lag ftnmd during a 40° eye rotation without the use of an afterimage). Previous studies have shown that the retina at the posterior pole can shift sufficiently to produce this effect The other “optical sliding” situation, crystalline lens tilting, could also allow foveal fixation while inducing an apparent Station lag. Unfortunately no research has studied this question of dynamic lens tilt However it is possible that the lens could tût 3.6° during extreme eye rotations, thereby inducmg a 14.5 minute of arc ocular lag. 173 Microsaccades occurred during fîxadon in all seven subjects. Over the range of nasal eye rotation angles 10“, 20“, 30“ and 40“), mean microsaccadic durations fell between 14.0 and 19.1 milliseconds. Mean amplitudes fell between 12.9 and 21.3 minutes of arc, and mean peak velocities fell between 23.6 and 34.8 degrees/second. Microsaccade duration, amplitude and peak veloci^ data were similar to those feund in previous studies, except for a slightly higher mean peak veloci^ finding. This was thought due to the inadequacy of the equipment in detecting slow-velocity microsaccades, and/or the presence of voluntary saccades in the data. Nevertheless, main sequence plots detailing microsaccade data of this research fit neatly within the main sequence plots of previous microsaccade and saccade studies. This supports the theory that a single physiological oculomotor control is responsible for both microsaccades and voluntary saccades. It is possible that both microsaccade amplitude and peak veloci^ increased with angle of eye rotation, but additional research is necessary before this association can be made with confidence. End-gaze nyst%mus occurred in two o f the seven subjects, and only during 40“ eye rotations. All cases fit typical nystagmus criteria: amplitudes were between 025 and 5 degrees, fiequencies between 1 and 5 Hz and peak velocities were £ 100 degrees/second. This research provided data detailing characteristics of the nystagmus’ fast phase component: mean duration was 21.8 milliseconds, mean amplitude was 26.9 minutes of arc and mean peak velocity was 33.3 degrees/second. These characteristics were similar to those of microsaccades and saccades. This was an expected r^ult since the fast phase component of jerk nystagmus is considered a saccadic eye movement. Overall, end-gaze nystagmus data firom this research were similar to those found in previous studies, except the direction of slow and fast phases in one case; the slow phase of nystagmus took the eye away firom primary gaze, while the fast phase moved the eye toward primary gaze. Excessive innervation provided by the cerebellum to the conjugate neural integrator could, in theory, explain this phenomenon. Unfortunately end-gize nystagmus occurred in only two subjects, and only during eye rotations of 40“; no formal statistical analyses were performed on this data. 174 62 SCLERAL SEARCH COH, SLIPPAGE It was concluded that scierai search coil slippage can occur during extrone nasal gazes. Scleral lens slippage was always in the temporal direction, possibly due to contact between the lens and the eyelids. Furthamore, lais slippage progressively increased with the angle of eye rotation (p =0.011). Overall, mean lens slippage was 0.0,2.0,5.0,11.9 and 233 minutes o f arc for nasal eye rotations of 0“, 10°, 20°, 30° and 40°, respectively. With 95% confidence, significant slippage occurred in the sample while subjects fixated nasally 30° and 40°. Search coil slippage varied between subjects. Some subjects showed more overall search coil slippage (p <0.0005), and some subjects had larger unit increases in search coil slippage as the angle of eye rotation increased (p <0.0005). However, the standard deviations for slippage were small for all subjects at each eye rotation angle. Therefore the scleral lens repeatedly slipped to a specific position for each nasal eye rotation, and then repeatedly slipped back to its original position as the eye returned to primary gaze. This result supports the idea that the scleral lens and bulbar conjimctiva both slide during eye movement. Small standard deviations for slippage at each eye rotation angle in individuals made it possible to treat slippage as a constant error in fixation position data collected by the scleral search coil equipment. 175 APPENDIX A INFORMED CONSENT FORM 176 THE OHIO STATE UNIVERSITY Protocol No. 98H0360 CONSENT To DMVESTIGATIONAL TREATMENT OR PROCEDURE I.______, hereby authorize or direct Dr. Nick Poet's aMociates or assistants of his/her choosing, to perform the foltowing treatment or procedure (describe in general terms). In this experiment, a specially designed contact lens will be placed on my right eye by a licensed optometrist to measure eye movements.. The contact lenses are carefully disinfected before and after each use by the experimenter. Anesthetic will be applied to tvy right q e to reduce discomfort. My left eye will be covered with a patch, I will hold my head in position by biting onto a dental-impression o f my teeth, and I will assist in positioning my head in the correct location. All measurements are taken in a dark room. In the first half of the experiment, measurements will be taken while I view various light targets ahead o f me. Later, a light will be flashed at my right eye While this light is shone at a safe level the light will still be seen after the flash as an "after image" In the second half of the experiment, 1 will aim my eye with the after-image toward various light targets ahead o f m e This light will disappear fiom sight over a period o f minutes. Prior to participation in this study, the experimenter will ask me about my ocular and systemic health and hiaory, and whether or not 1 may be pregnant. 1 will not be allowed to participate in this study if pregnant upon (myself or name of subject) The experimental (research) portion o f the treatment or procedure is: The research portion of this experiment is to monitor the alignment of my gaze while 1 look at the targets, both with and without the after-image being present The specially designed contact lenses and the accompanying eye movement monitor are commercially available. This is done as part of an investigation entitled: The accuracy and precision of extreme-gaze ocular fixation in sparse visual surroimdings. Purpose o f the procedure or treatment: The purpose of this experiment is to measure the alignment o f my gaze while 1 look at the targets, both with and without the sAer-image being present Possible appropriate alternative procedure or treatment (not to participate in the study is always an option): 1 may choose to not participate at any time during the experiment My grades will not be adversely effected if 1 choose not to participate, or if 1 withdraw fiom partidpatioit Discomforts and risks reasonably to be expected: 1 may experience mild irritation fiom the contact lens. 1 may also experience mild eye irritation if 1 am allergic to the topical anesthetic. Irritation symptoms may include mild redness, mild tearing, mild itching and mild burning of the eye I stilt may notice the after-image in my vision for a number of minutes after completion o f the study session. There will be no permanent changes to my vision. Possible benefits for subjects/society: 1 will not benefit fiom this stut^, other than being paid $10 per session (five sessions maximum). This experiment should help the researchers to understand if and how ^ e alignment with a target changes as the eye rotates to cfifiTerent angles. FORM 1; Difonned consent foim. (continued) 177 FORM 1 continued Anticipated duration of subject’s participation (inciuding number o f visits): Maximum of 2.5 hours total; No more than 30 minutes per session I hereby acknowledge that______has provided information about the procedure described abovey about my rights as a subject; and he/she answered ail questions to my satislhction. I understand that I may contact him/her at Phone No, f614> 688-4594 should I have additional questions. He/She has explained the risks described above and I understand them; he/she has also offered to explain all possible risks or complications, I understand that, where appropriate, the U.S, Food and Drug Administration may inspect records pertaining to this study, I understand fhrther that records obtained during my participation in this study that may contain my name or other personal identifiers may be made available to the sponsor o f this study. Beyond this, I understand tiiat my participation will remain confidentiaL I understand that I am free to withdraw my consent and participation in this project at any time after notifying the project director without prejudicing future care. No guarantee has been given to me concerning this treatment or procedure. I understand in signing this form that, beyond giving consent, 1 am not waiving any legal rights that I might otherwise have, and I am not releasing the investigator, the sponsor, the institution, or its agents from any legal liability for damages that they might otherwise have. In the event of injury resulting from participation in this study, I also understand that immediate medical treatment is available at University Hospitals of The Ohio State University and that the costs of such treatment will be at my expense; financial compensation beyond that required by law is not available. Questions about this should be directed to the Office of Research Risks at 292-5958, [ have read and fdlfy understand the consent form, I sign it freely and voluntarily. A copy has been given to me. Date:______Time:______AM PM Signed:______(Subject) Witness (es):______if requited (Person Authorized to Consent for Subject if Required) 1 certify that I have personally completed all blanks in this form and explained them to the subject or his/her representatnre before requesting the subject or his/her representatwe to sign it. Date:______S^ed_ (Signature of Project Director or his/her Aulhorned Representative) 178 APPENDIX B COMPUTER PROGRAMS 179 PROGRAM 1: Horizontal and vertical scleral s ^ c h coil calibration program. The computer form is shown above, while the code is listed on the following pages. 180 "Horizontal and Vertical Coil Calibration Program "By: Tyson J. Bnmstetter, OD., M.S. "Date: June 23,1998, Revised May 21,1999 "Adapted from: Computer Boards, Inc. Universal Library Rev 4.0 'File: Calibrate.vbp 'Purpose: Reads two A/D Input channels while the search coil is turned in horizontal directions of-10,0,10,20,30,40,50 and in vertical dhrections of-10,0,10 degrees. The horizontal and vertical data are saved in separate, user-defined files within: C:\TysonCal\'*.dat. Library calls: cbAInScan%0, cbErrHandling%0, cbDeclareRevisionO, cbWinBufAlloc%0, ' cbWmBufToArray% 'Requirements: * Board 0 must have an A/D converter. * Analog signal on an input channel. 'Include CBW32.bas 'Mandatory include file to access default parameters Const BoardNum% = 0 ' Board number Const NumPointsA = 10000 ' Total number of data points to collect Const FirstPoint& = 0 'set first element in buffer to transfer to array Dim ADData%(NumPoints&) ' dimension an array to hold the input values Dim MemHandIe% ' deAie a variable to contain the handle for ’ memory allocated by Windows through cbWinBufAlloc%0 Private Sub CmdO_CIickO LowChan% = 0 ’ first channel to acquire HighChan% = 0 ' last chaimel to acquire CBCount& = (NumPoints& /10) ' total number of data points to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS 'set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer easts ÜLStat% =cbAIhScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.'*, 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data &om the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat%= cb WmBufroArray%(MemHandIe%, ADData%(0), FhstPoiht&, CBCount&) If ULStat% o 0 Then Stop 181 Fori% = 0To999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j=ADData%(i%) + 0 End If Print #l,j LabeIData.Captîon = Fonnat$(ADData%(i%), "0") LabeIRate.Caption = Fonnat$(CBRate&, "0") LabelPoints.Caption = Formal$(CBCount&, "0") Nexti% CmdlOÆnabled = I CmdOÆnabled = 0 End Sub Private Sub CmdlO ClickQ LowChan% = 0 ' first channel to acquire HighChan% = 0 ' last channel to acquire CBCount& = (NumPoints& / 10) ' total number of d^ points to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data fiom the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print# I, j LabeIData.Captfon = Formal$(ADData%(i%), "0”) LabeIRate.Caption = FormatS(CBRate&, "0") LabeIPoints.Caption= Format$(CBCount&, "0") Nexti% Cmd20.EnabIed= I 182 CmdlO^nabled = 0 End Sub Private Sub Cmd20_ClickO LowCban% = 0 ' fust channel to acquire H!ghChan% = 0 ' last channel to acquhre CBCount& = (NumPoints& / 10) ' total number of data pomts to collect = 1000 CBRate& = 500 ‘ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS ' set the gain [f MemHandle% = 0 Then Stop ' check that a handle to a memory bu%r exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%)’ If ULStat% = 30 Then R^gBox "Change the Gain% argument to one supported by this board.”, 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPointA, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j LabelData.Caption = Format$(ADData%(i%), "0") LabelRate.Caption = Format$(CBRate&, "0") LabelPomts-Caption = Formatf(CBCount&, "0") Nexti% Cmd30.Enabled = t Cmd20.Enabled = 0 End Sub Private Sub CmdSOjClickQ LowChan% = 0 ' first channel to acquire HighChan% = 0 ' last channel to acqufre CBCount& = (NumPomts& / 10) ' total number of data points to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options»/»= NOCONVERTDATA ' use NOCONVERTDATA if usmg 16 bit board Gam% = BIP5VOLTS 'setthe gam 183 [f MemHandle% = 0 Then Stop ' check that a handle to a memory bu ^ r exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) [f ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data fiom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For 1% = 0 To 999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j LabeIData.Caption = Format$(ADData%(i%), "0") LabeIRate.Caption = Format$(CBRate&, "0") LabeiPoints.Caption = FormaÀ(CBCount&, "0") Next i% Cmd40.EnabIed = I CmdSOÆnabled = 0 End Sub Private Sub Cmd40_CIickO LowChan% = 0 ' first channel to acqufie HighChan% = 0 ' last channel to acquire CBCount& = (NumPoints& /10) ' total number of data points to collect = 1000 CBRate& = 500 'sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gam If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then B^gBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% <>91 Then Stop ' Transfer the data fi-om the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cb WmBufroArr^f%(MemHandI^, ADData%(0), FfistPomt&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 999 184 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,J LabeIData.Caption = FonnatS(AOOata%(i%), "0") LabelRate.Caption = Format$(CBRate&, "0") LabelPoints-Caption = FormatS(CBCount&, ”0") Nexti% Cmd40ÆnabIed = 0 Cmd50£nabled = I End Sub Private Sub Cmd50_CIickO LowChan% = 0 ' first channel to acquire HighChan% = 0 'last channel to acquire CBCount& = (NumPoints& /10) ' total number of data points to collect = 1000 CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HlghChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else i = ADData%(i%) + 0 End If Print #I,J LabeIData.Caption = FormatS(ADData%(i%), "0") LabeIRate.Capûon = Format$(CBRate&, ”0") LabeIPomts.Caption = Fonnat$(CBCount&, "0") Notti% Cmd50.EnabIed = 0 Close #I 185 End Sub Private Sub CmdDownIO_CIickO LowChan% = 1 ' first channel to acquire HighChan% = I ' last channel to acquire CBCount& = (NumPoints& /10) ' total number of dma pomts to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS 'set the gam If MemHandle% = 0 Then Stop * check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then ^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If f*rint#2,J LabelData.Caption = Format$(ADData%(i%), "0") LabelRate.Caption = Format$(CBRate&, "0") LabeiPoints.Caption = FormatS(CBCount&, "0") Nexti% CmdZeroÆnabled = 1 CmdDown 10.Enabled = 0 End Sub Private Sub CmdExftjClickO ULStat% = cbWinBufFree%(MemHandle%) If ULStat% o 0 Then Stop End End Sub Private Sub CmdNeglOjCIickQ 186 LowChan% = 0 ' Gist channel to acquire HighChaa% = 0 ' last channel to acquire CBCount& = (NumPoints& /10) ' total number of points to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ' set the gain [f MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% - cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData»/o(i%) + 0 End If Print #1,J LabeiData.Caption = Format$(ADData%(i%), "0") LabelRate.Caption = FormatS(CBRate&, "0") LabelPoints.Caption = Format$(CBCount&, "0") Next i% CmdNeg 10.Enabied = 0 CmdOÆnabled = 1 End Sub Private Sub CmdUp lO CIlckQ LowChan% = 1 ' fust channel to acquue HighChan% = 1 ' last channel to acquue CBCount& = (NumPoints& /10) ' total number of data pomts to collect = 1000 CBRate& = 500 ' samplmg rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if usmg 16 bit board Gam% = BIP5V0LTS 'set the gam If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighCban%y CBCount&, CBRateA, Gain%, MemPbndle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.”, 0, 187 "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buf&r set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To999 If ADData%(i%) < 0 Then i = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #2, j LabeIData.Caption = Format$(ADData%(i%), "0") LabeIRate.Caption = Format$(CBRate&, "0") LabelPoints.Caption = FormatS(CBCount&, "0") Nexti% CmdUp 10 JEnabled = 0 End Sub Private Sub CmdZero ClickQ LowChan% = I ' first chaimel to acquire HighChan% = I * last chaimel to acquire CBCount& = (NumPoints& /10) ' total number of data points to collect = 1000 CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, NdemHandle%, Options%) If ULStat% = 30 Then ^^gBox "Change the Gain% argument to one supported by this boarcL'\ 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data fiom the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPomt&, CBCount&) If ULStat% o 0 Then Stop Fori%=0To999 If ADData%(i%) <0 Then j = ADData%(i%)+65536 Else j=ADData%(i%)+0 188 End If Print #2» j LabelData.Caption = Format$(ADData%(i%), "0") LabelRate.Caption = Format$(CBRate&, "0") LabeIPoints.Caption = Format$(CBCount&, "0") Next i% CmdUp IO.EnabIed= I CmdZero.Enabled = 0 End Sub Private Sub Commandl CIickQ Open HorizontalFiIe.Text For Output As CmdNeg I O.Enabled= I Command I Enabled = 0 End Sub Private Sub Coramand2_CIickO Open VerticalFiIe.Text For Output As #2 CmdDownIO.Enabled= I CommandZÆnabled = 0 End Sub Private Sub Form LoadQ ' declare revision level of Universal Library ULStat% = cbDecIareRevision(CURRENTREVNUM) ' Initiate error handling ’ activating error handling will trap errors like ' bad channel numbers and non-configured conditions. ' Parameters; ' PRINTALL rail warnings and errors encountered will be printed ’ DONTSTOP :if an error is encountered, the program will not stop, errors must be handled locally ULStat% = cbErrHandlmg%(PRINTALL, DONTSTOP) If ULStat% o 0 Then Stop ' If cbErrHandIihg% is set for STOPALL or STOPFATAL durmg the program ’ design stage. Visual Basic will be unloaded when an error is encountered. ' We suggest trapping errors Ioca% until the program is reac^ for compQmg ' to avoid losmg unsaved data during program design. This can be done by ' setting cbErrHandlmg options as above and checkmg the value of ULSt^% 189 ’after a call to the library, [f it is act equal to 0, an error has occurred. MemHandle% = cbWmBufA.lloc%(NuniPomts&) ’ set aside memory to hold data If MemHandle% = 0 Then Stop End Sub 190 Al * ui.](: y .jriiJ P ic c r - m n iif J ix.ihufi in f xlft-intr l y .un J [* i ijrr.h;! I n 1 . The computer fbim is shown above, while the code is listed on the following pages. 191 ’Program to Measure the Accuracy and Precision o f fixation in Extreme Gazes "By: Tyson J. Brunstetter, O J)., M.S. 'Date: July 20,1998; Revised: March 18, May 17 and 21,1999 'Adapted firom: Computer Boards, hic. Universal Library Rev 4.0 'File: PhD.vbp 'Purpose: After the subject fbcates the point object, this program reads two A/D Input channels (0 = horizontal, I = vertical). The combined d ^ are saved in a user defined fHe within: C:\TysonPhD\Data\*.dat 'Library calls: cbAlnScan%0, cbDBitOut%0. cbDConfigPort%0, cbDeclareRevisionO, ' cbDOut%0, cbErrHandling%0, cbWmBu£AUoc%0, cbWinBufFree%0> cbWmBufroArray%0 'Requirements: ""Board 0 must have an A/D converter. *Board 0 must have two digital output ports. * Analog signal on an input channel. 'Include CBW32.bas 'Mandatory include file to access default parameters Const BoardNum% = 0 "Board number Const NumPoints& = 2000 Total number of data points to collect Const FirstPoint& = 0 'Set first element in buffer to transfer to array Const PortNum% = FIRSTPORTA Use "A" digital port for LED output Const PortNum2% = FIRSTPORTB Use "B" digital port for LED output Const Dfrection% = DIGITALOUT 'Program first digital port for "output" mode Dim ADData%(NumPoints&) 'Dimension as array to hold the input values Dim MemHandIe% 'Define a variable to contain the handle for memory ' 192aIIocated by Windows through cbWinBufAlIoc%0 Private Sub ChecklOA_ClickO CmdlO IOA.Enabled = I OrderListAddltem " 10; 10,0" End Sub Private Sub Check lOBjClickQ CmdlOIOBÆnabled = I OrderListAddltem " 10; 10,0" End Sub Private Sub ChecklOC CIickQ CmdlOlOCJEnabled = I OrderListAddltem " 10; 10,0" End Sub Prwate Sub Check20A_CIickO Cmd2020AEhabled = I OrderListAddltem " 20; 20,0" End Sub 192 Private Sub Check20B_CIickO Cmd2020BÆnabIed = I OrderListAddltem " 20; 20,0" End Sub Private Sub Check20C_CIfckO Cmd2020CÆnabIed = I OrderListAddltem" 20; 20,0" End Sub Private Sub Check30A_CIickO Cmd3030A.EnabIed = I OrderListAddltem " 30; 30,0" End Sub Private Sub Check30B_ClickO Cmd3030BÆnabled = I OrderListAddltem " 30; 30,0" End Sub Private Sub Check30C_CIickO Cmd3030C.EnabIed = I OrderListAddltem " 30; 30,0" End Sub Private Sub Check40A_ClickO Cmd4040AÆnabled = I OrderListAddltem " 40; 40,0" End Sub Private Sub Check40B_CIickO Cmd4040B^nabied = I OrderListAddltem " 40; 40,0" End Sub Private Sub Check40C_CIickO Cmd4040CEnabIed = I OrderListAddltem " 40; 40,0" End Sub Private Sub CheckAIIOA ClickQ CmdAIlOOA.EnabIed= t OrderListAddltem " 10; 0 AI" End Sub Private Sub CheckAIlOBjCIickO CmdAIIOOB£nabIed= 1 OrderListAddltem " 10; 0 AI" End Sub Private Sub CheckAIIOCjClickO CmdAIlOOCÆnabied = I 193 OrderListAddltem " 10; 0 AI" End Sub Private Sub CheckAI20A_CIickO CmdAI200A.EnabIed = l OrderListAddltem " 20; 0 AI" EndSub Private Sub CheclcAI20B_CIickO CmdAI200B.Enabled = l OrderListAddltem " 20; 0 AI" EndSub Private Sub CheckAI20C_CIickO CmdAI200C>EnabIed = l OrderListAddltem " 20; 0 AI" End Sub Private Sub CheckAI30A_CIickO CmdADOOAÆnabled = l OrderListAddltem " 30; 0 AI" End Sub Private Sub CheckAI30BjCllckO CmdAI300BÆnabled = I OrderListAddltem " 30; 0 AI" End Sub Private Sub CheckAI30C_ClickO CmdAI300C^abIed = l OrderListAddltem " 30; 0 AI" End Sub Private Sub CheckAI40A_CIickO CmdAI400AÆnabled = I OrderListAddltem " 40; 0 AI" End Sub Private Sub CheckAI40B_CIickO CmdAMOOBÆnabled = I OrderListAddltem " 40; 0 AI" End Sub Private Sub CheckAI40C_CIickO CmdAI400CÆnabled = l OrderListAddltem " 40; 0 AI" EiidSub Private Sub CmdOOAjCKckQ PortType% = PortNum% BitNum% = 0 BitVaIue% = I 194 ULStat% = cbDBitOiit%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.Vaiue = I EndSub Ehivate Sub CmdOOA_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ’ last channel to acquire (vertical) CBCount& = (NumPoInts&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA If using 16 bit board Galn% = BIP5V0LTS ' set the gain If MemHandle% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Galn%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufToArray%(MemHandle%, ADData%(0), FIrstPomt&, CBCount&) If ULStat% o 0 Then Stop ForI% = OTo 1999 If ADData%(I%) < 0 Then i = ADData%(I%) + 65536 Else j = ADData%(I%) + 0 End If Print #I,j Nextl% Beep PortType% = PortNum% BItNum% = 0 BItVaIue% = 0 ULStat% = cbDBItOut%(BoardNum, PortType%, BhNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.Value=0 ChkButtomValue = 0 195 ChkLEDoÉf-Value = I CmdOOAÆnabled = 0 CmdO lOAÆnabled = I End If EndSub Private Sub CmdOOB_CIickO PortType% = PortNum% BitNum% = 0 BitVaIue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = 1 EndSub Private Sub CmdOOB_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0ToI999 If ADDato%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,i Nocti% Beep 196 PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNunu PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.Value = 0 ChkLEDoffValue = I CmdOOBEnabled=0 Cmd020AEnabled = I End If EndSub Private Sub CmdOOCjCIickO PortType% = PortNum% BitNum% = 0 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = I EndSub Private Sub CmdOOC_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of d ^ points to collect (see General Code) CBRate& = SOO ' sampling rate (samples per second) Oprions% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gam If MemHandIe% = 0 Then Stop ' check that a handle to a memory bufter exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gam%, VIemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data fiom the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWmBufFoArray%(MemHandIe%, ADData%(0), FirstPomt&, CBCount&) If ULStat% o 0 Then Stop 197 Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%)+0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon.Value = 0 ChkButton. Value = 0 ChkLEDoff. Value = I CmdOOCJEnabled = 0 CmdOSOAÆnabled = I End If End Sub Private Sub CmdOOD_ClickO PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BcardNum, PorfType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon.VaIue = I End Sub Private Sub CmdOOD_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.VaIue= I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPomts&) ' total number of data points to collect (see General Code) CBRate& = 500 'sampling rate (samples per second) Options»/» = NOCONVERTDATA ’ use NOCONVERTDATA if usmg 16 bit board Gam% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory bufkr exists 198 ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gam%, MemHandle%, Options%) If ULStat% = 30 Then t^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory bufiër set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print #l,j Next i% Beep PortType% = PortNum% BitNum% = 0 BitVaiue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.VaIue= I CmdOOD.Enabled = 0 Cmd040A.EnabIed = I End If End Sub Private Sub CmdOOEjCIickO PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = I End Sub Private Sub CmdOOE_MouseDown(Button As Integer, Shift As Integer, X As Smgle, Y As Single) If Button = 2 Then ChkButton. Value = I 199 LowChaa% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquhe (vertical) CBCount& = (NumPomts&) ' total number of dîûa points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options®/» = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, N/ïemHandle%. Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray®A(MemHandle®/o, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 1999 If ADData%(i%) < 0 Then j = ADData®/o(i®/o) + 65536 Else j = ADData®/o(i®/o) + 0 End If Print #l,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cfaDBitOut®/o(BoardNum, PortType%, BitNum®/», BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.VaIue = 0 ChkLEDofflVaIue= I CmdOOEÆnabled = 0 ChecklOAÆnabled = I Check20AJBnabled= I Check30A-Enabled= I Check40A.Enabled= I OrderList.AddItem " Head; Eye" End If End Sub Private Sub CmdOIOAjClickQ PortType% = PortNum% 200 BitNum% = I BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub CmdOIOA_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button =2 Then ChkButton. Value = I LowChan% = 0 ' Erst channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& - (NumPoints&) ' total number of d ^ points to collect (see General Code) CBRate& = 500 ' samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print#I,j Nexti% Beep PortType% = PortNum% BitNum% = I BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, Porffype%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value=0 201 ChkButton.Value=0 ChkLEDoff.Value = I CmdOIOA.EnabIed = 0 CmdOOB.£nabIed = I End If End Sub Private Sub Cmd020A_CIickO PortType% = PortNum% BitNum% = 2 BitValue% = L ULStat% = cbDBitOut%(BoardNum, PorfType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff-Value = 0 ChkLEDon.Value = I End Sub Private Sub Cmd020A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% = I ’last channel to acquire (vertical) CBCount& = (NuntPoints&) ’ total number of data points to collect (see General Code) CBRate& = SOO 'sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS ’ set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data ftom the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) <0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Prmt#I,j Necti% Beep 202 PortType% = PortNum% BitNum% = 2 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = 1 Cmd020A.EnabIed = 0 CmdOOCÆnabled = 1 End If End Sub Private Sub CmdOSOAjClickQ PortType% = PortNum% BitNum% = 3 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon.Value = 1 End Sub Private Sub Cmd030A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value = 1 LowChan% = 0 ' first channel to acquire Qiorizontal) HighChan% =1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) 'total number ofd^pomts to collect (see General Code) CBRate& = SOO 'samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data firom the memory buffer set up by Windows to an array for use by Visual Basic ULStat%= cb WmBufroArray%(MemHandIe%, ADData%(0), FnstPomt&, CBCount&) IfULStat% o 0 Then Stop 203 Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(L%) + 65536 Else j = ADData%(i%)+0 End If Print #Uj Nexti% Beep PortType% = PortNum% BitNum% = 3 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.VaIue = I Cmd030A.EnabIed = 0 CmdOOD.Enabted = I End If End Sub Private Sub Cmd040A_ChckO PortType% = PortNum% BitNum% = 4 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon.VaIue = I End Sub Private Sub Cmd040A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button =2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquhe (vertical) CBCount& = (KumPomts&) ' total number of data points to collect (see General Code) CBRate& = 500 'samplmg rate (samples per second) OptionsVo = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ' set the gam If MemHandIe%=0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAhiScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gam%, MemHandIe%, Options%) 204 If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data &om the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 4 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon.Value = 0 ChkButton. Value = 0 ChkLEDoff.VaIue= 1 Cmd040A.Enabled = 0 CmdOOE.Enabled = 1 End If End Sub Private Sub CmdlOOAjClickQ PortType% = PortNum% BitNum% = 0 BitValue%= I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub CmdIOOA_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Smgle) IfButton=2Then ChkButton.Value = I LowChan% = 0 ' fust channel to acquire (horizontal) 205 HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ’ total number ofrfata points to collect (see General Code) CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’set the gain If MemHandle% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j=ADData%(i%) + 0 End If Print #1,J Next i% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoffValue = I CmdlOOAEnabled = 0 Checkl OBEnabled = I End If End Sub Private Sub CmdlOOB CIickQ PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNum^ PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop 206 ChfcLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub CmdlOOB_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquhe (horizontal) HighChan% = 1 ’ last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gam If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan*’/o(BoardNum%, LowChan%, HighChanVo, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then R^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% -o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData“/o(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,i Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.Value = 0 ChkLEDoffValue = 1 CmdlOOBEnabled=0 ChecklOCEnabled = 1 End If 207 End Sub Private Sub CmdlOOCjClickO PortType% = PortNum% BitNum% = 0 BitVaIue% = 1 ULStat% = cbDBitOut%(BoardNuni^ PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = I End Sub Private Sub CmdlOOC_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data pomts to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) <0 Then j = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BftNum% = 0 BitVaIue%=0 208 ULStat% = cbDBitOut%(BoardNum, PortType%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.VaIue = 0 ChkButton. Value = 0 ChkLEDoffValue = I CmdlQOC£nabled = 0 CheckAI lOAÆnabled = I End If End Sub Private Sub Cmdl 0 lOA ClickQ ChecklOAJEnabled = 0 PortType% = PortNum% BitNum% = I BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub CmdIOIOA_MouseOown(Button As Integer, Shift As Integer. X As Single, Y As Single) If Button = 2 Then ChkButton.Value = I LowChan% = 0 ' fust channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 'sampling rate (samples per second) Options»/» = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS 'set the gain If MemHandIe% = 0 Then Stop ’ check that a handle to a memory buffer adsts ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gam” If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat%= cbWmBufToArray%(MemHandIe%, ADData%(0), FustPomt&, CBCount&) If ULStat% o 0 Then Stop Fori%=OTo 1999 If ADData%(i%) < 0 Then 209 j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Nexti% Beep PortType% = PortNum% BitNum% = I BitValue% = 0 ULStat% = cbDBitOut%(BoardNunu PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDofF.VaIue = I CmdIOIOA.EnabIed = 0 CmdIOOA.EnabIed= I End If End Sub Private Sub CradIOlOB_ClickO Checkl OBÆnabled = 0 PortType% = PortNum% BitNum% = I BitValue% = I ULStat% = cbDBitOut%(BoardNunu PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDofflValue = 0 ChkLEDon. Value = I End Sub Private Sub CmdIOIOB_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' ftrst channel to acquire (horizontal) HighChan% = I ' last channel to acqunre (vertical) CBCount& = (NumPoints&) ' total number ofdata, pomts to collect (see General Code) CBRate& = 500 ' samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAftiScan%@oardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) 210 If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = GTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,J Nexti% Beep PortType% = PortNum% BitNum% = L BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = I Cmd 10 IOB.Enafaled = 0 CmdlOOB.Enabled = 1 End If End Sub Private Sub CradI010C_ClickO CheckIOC.Enabled = 0 PortType% = PortNum% BitNum% = I BitVaIue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue=0 ChkLEDon.Value = I End Sub Private Sub CmdlOlGC_MouseDown(Button As hiteger. Shift As hiteger, X As Single^ Y As Single) IfButton=2Then ChkButton.Value= I 211 LowChan% = 0 ' Qrst channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gain% = B1P5V0LTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Opuons%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #1,J Next i% Beep PortType% = PortNum% BitNum% = 1 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon.Value = 0 ChkButton. Value = 0 ChkLEDoffValue = 1 CmdlO 10C.EnabIed = 0 CmdlOOCÆnabled = 1 End If End Sub Private Sub CmdlOOAjClickQ PortTyp^ = PortNum% BitNum% = 0 BhValue% = I ULStat%= cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop 212 ChkLEDoff-Value = 0 ChkLEDon-Value = 1 End Sub Private Sub Cmd200A_MouseDown(Button As Integer, Shift As hiteger, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options»/» = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) IfULStat% o O Then Stop For i% = 0 To 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton-Value = 0 ChkLEDoffValue = I CmtBOOAEnabled = 0 Check20BEiiabIed = I End If 213 End Sub Private Sub Cmd200B_CIfckO PortType% = PortNum% BitNum% = 0 BitValue% = I ULStat% = cbDBrtOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.Value = L End Sub Private Sub Cmd200B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first chaimel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number ofdata, points to collect (see General Code) CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If VIemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then R^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Wmdows to an array for use by Visual Basic LTLStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) IfULStat% o 0 Then Stop Fori% = 0To 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Prmt#l,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 214 ULStat% = cbDB[tOut%(BoardNum, PortType%, BttNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoiuValue = 0 ChkButton. Value = 0 ChkLEDoffValue = I Cmd200B.EnabIed. = 0 Check20C£nabIed= 1 End If End Sub Private Sub Cmd200C_ClickO PortType% = PortNum% BitNum% = 0 BitValue% = 1 ULStat% = cbDBitOut%(BoardNunu PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = 1 End Sub Private Sub Cmd200C_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% = 1 ’ last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = B1P5VOLTS set the gain If MemHandle% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAinScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data 6om the memory bufkr set up by Windows to an array for use by Visual Basic ULStat% = cbWnaBufroArray%(MemHandIe%, ADData%(G), FnstPomt&, CBCount&) If ULStat% o 0 Then Stop Fori%=0Tol999 If ADData%(i%) < 0 Then j = ADData“/o(i%) + 65536 215 Else j = ADData%(i%) + 0 End If Print #l,j N«cti% Beep PoitType% = PortNum% BitNum% = 0 BrtValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = I Cmd200C.£nabIed = 0 CheckAI20A.EnabIed = I End If End Sub Private Sub Cmd2020A_CIickO Check20A.Enabled = 0 PortType% = PortNum% BitNum% = 2 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BttNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon.Value = I End Sub Private Sub Cmd2020A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value= 1 LowChan% = 0 ' fhst channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data pomts to collect (see General Code) CBRate& = SOO ’samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ’ set the gam If MemHandIe% = 0 Then Stop ’ check that a handle to a memory bu&r exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gam%, MemHandIe%, Options%) If ULStat%=30 Thea MsgBox "Change the Gam% argument to one supported by this board.", 0, 216 "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data firom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADOata%(0), FhstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #Uj Next i% Beep PortType% = PortNum% BitNum% = 2 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNuitu PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = I Cmd2020A.EnabIed = 0 Cmd200A.EnabIed = I End If End Sub Private Sub Cmd2020B_CIickO Check20B.Enabled = 0 PortType% = PortNum% BitNum% = 2 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDofF.VaIue=0 ChkLEDon. Value = I End Sub Private Sub Cmd2020B_V(ouseDown(Button As Integer, Shift As Integer, X As Smgle, Y As Smgle) IfButton = 2Then ChkButton.VaIue = I 217 LowChan% = 0 ' fnrst channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) C6Count& = (NumPoints&) ’ total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = B1P5V0LTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buAer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRateA, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print #l,j Next i% Beep PortType% = PortNum% BitNiun% = 2 BitValue% = 0 ULStat% = cbOBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoffValue = I Cmd2020B.Enabled = 0 Cmd200B.Enabled= 1 End If End Sub Private Sub Cmd2020C ClickQ Check20C.Enab(ed=0 PortType% = PortNum% BitNtnn% = 2 BitValue% = I 218 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue=0 ChkLEDon.Vaiue = I End Sub Private Sub Cmd2020C_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ Erst channel to acquhre (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = SOO ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 2 BitVaIue% = 0 ULStat% = cbDBftOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoo-Value=0 ChkButtomValue=0 ChkLEDoffValue = I 219 Cmd2020C.EnabIed = 0 Cmd200C.£nabIed = I End If End Sub Private Sub Cmd300A_CUckO PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBttOut%(BoardNunu PortType%, BttNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = I End Sub Private Sub Cmd300A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = SOO ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory bufter exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Priht#I,j Nexti% Beep 220 PortType% = PortNum% BitNum% = 0 BitVaIue%=0 ULStat% = cbDBitOut%(BoardNum, PortType%» BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon-Value = 0 ChkButton.VaIue=0 ChkLEDoff-Value = I CmdSOOA-Enabled = 0 Check30B-EnabIed = I End If End Sub Private Sub CmdSOOBjCIickQ PortType% = PortNum% BitNum%=0 BitVaIue% = I ULStat% = cbDBttOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff-Value = 0 ChkLEDon-Value = I End Sub Private Sub Cmd300B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton-Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last chatmel to acquire (vertical) CBCount& = (NumPoints&) ' total number of dûa pomts to collect (see General Code) CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS ’ set the gam If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then B^gBox "Change the Gain% argument to one supported by this board-", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cb WmBufToArray%(MemHandIe%, ADData%(0), FftstPomt&, CBCount&) If ULStat% o 0 Then Stop 221 Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #Uj Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBttOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.VaIue = 0 ChkButton. Value = 0 ChkLEDoff. Value = I Cmd300B.EnabIed - 0 CheckSOC.Enabled = I End If End Sub Private Sub Cmd300C_ChckO PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNunw PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = I End Sub Private Sub Cmd300C_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' fust channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data pomts to collect (see General Code) CBRate& = 500 ' samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS 'set the ^m If MemHandIe%=0 Then Stop ’ check that a handle to a memory bufiër exists ULStat%= cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gam%, 222 MemHandIe%^ Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data 6om the memory buSer setup by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHantUe%, ADData%(0), FirstPoiht&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff:Value= I Cmd300C.EnabIed = 0 CheckAI30A.EnabIed = I End If End Sub Private Sub Cmd3030A_CIickO Check30A£nabIed = 0 PortType% = PortNum% BitNum% = 3 BitVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue=0 ChkLEDon.VaIue= I End Sub Private Sub Cmd3030A_MouseOown(Button As hiteger. Shift As Integer, X As Single, Y As Single) If Button=2 Then ChkButton.VaIue= I 223 LowCban% = 0 ' Grst channel to acquire (horizontal) HlghChan% = I ’ last channel to acquire (vertical) CBCount& = (NumPomts&) ' total number of data pomts to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = B1P5V0LTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, VfemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print#l,j Nexti% Beep PortType% = PortNum% BitNum% = 3 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff Value = I Cmd3030A.Enabled = 0 Cmd300AÆnabled = 1 End If End Sub Private Sub Cmd3030B_ClickQ Check30B£nabled=0 PortType% = PorfKum% BitNum% = 3 BitVaIue% = 1 224 ULStat% = cbOBitOut%(BoardNum, PortType%, BttNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDofF-Value = 0 ChkLEDon. Value = I End Sub Private Sub Cmd3030B_MouseDown(Button As Integer. Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% =1 ’last channel to acquire (vertical) CBCount& = (NumPoints&) ’ total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandle% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCountA, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j Netti% Beep PortType% = PortNum% BitNum% = 3 BitValue%=0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.Value=0 ChkButton. Value =0 ChkLEDoff.Value = I 225 Cmd3030BJEnabIed = 0 Cmd300B£nabIed = 1 End If End Sub Private Sub Cmd3030C_CIickO Checks OCJEnabled = 0 PortType% = PortNum% BitNum% = 3 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub Cmd3030C_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cb WinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = 0To 1999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print #l,j Nocti% Beep 226 PortType% = PortNum% BitNum% = 3 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BttNum%, BrtValue%) [f ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.VaIue= I Cmd3030C.EnabIed = 0 Cmd300C.Enabled = I End If End Sub Private Sub Cmd400A_CIickO PortType% = PortNum% BitNum% = 0 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff. Value = 0 ChkLEDon. Value = I End Sub Private Sub Cmd400A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& - (NumPoints&) ' total number of d ^ points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCoimt&, CBRate&, Gam%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argiunent to one supported by this board.", 0, "Unsupported gain" If ULStal% o 0 And ULStat% o 91 Then Stop ’ Transfer the data 6om the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWmBufroArray%(MemHandIe%, ADData%(0), FirstPomt&, CBCount&) If ULStat% o 0 Then Stop 227 Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j Nexti% Beep PorfType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = 1 Cmd400A.EnabIed = 0 Check40B.Enabled = I End If End Sub Private Sub Cmd400B_ClickO PortType% = PortNum% BitNum% = 0 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = 1 End Sub Private Sub Cmd400B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value = 1 LowChan% = 0 ’ rirst channel to acquhe (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if usmg 16 bit board Gain% = BIP5V0LTS ' set the gam If MemHandIe%=0 Then Stop ' check that a handle to a memory buffer exists 228 ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&^ Gam%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.”, 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.VaIue = 0 ChkButton.VaIue = 0 ChkLEDoffValue = I Cmd400B.Enabled = 0 Check40C.EnabIed = I End If End Sub Private Sub Cmd400C_ClickO PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNiun, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoff.VaIue=0 ChkLEDon.VaIue = I End Sub Efrroate Sub Cmd400C_MouseDown(Button As Integer, Shift As Integer, X As Smgle, Y As Smgle) If Button = 2 Then ChkButton. Value = I 229 LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ’ last channel to acquire (vertical) CBCount& = (NumPomts&) ’ total number of data points to collect (see General Code) CBRate& = 500 'samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if usmg 16 bit board Gam% = BIP5VOLTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&» Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori%=OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else J = ADData%(i%) + 0 End If Print #1,] Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = I Cmd400C.EhabIed = 0 CheckAI40A.Ei»bled = I End If End Sub Private Sub Cmd4040A_CIickO Check40AJEnabIed = 0 PortType% = PortNum% BitNum% =4 BitVaIue% = I 230 ULStat% = cfaDBitOut%(BoardNuin, PortType%, BitNum%, BitVaIue%) If ULStal% o 0 Then Stop ChkLEDoff.VaIue = 0 ChkLEDon. Value = I End Sub Private Sub Cmd4040A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% =1 'last channel to acquire (vertical) CBCount& = (NumPoints&) ’ total number of data points to collect (see General Code) CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandle% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAJnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then i = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Prmt#I,j Nexti% Beep PortType% = PortNum% BitNum%=4 BitVaIue% = 0 ULStat%=cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value=0 ChkButton. Value = 0 ChkLEDofF-Value = I 231 Cmd4040A.EnabIed = 0 Cmd400A.EnabIed= I End If End Sub Private Sub Cmd4040B_ClickO Check40B.EnabIed = 0 PortType% = PortNum% BitNum% = 4 BitValue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon.VaIue = I End Sub Private Sub Cmd4040B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = 1 LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ’ total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cb WinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) <0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Prmt#I,i Necti% Beep 232 PortType% = PortNum% BitNum% = 4 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = I Ctnd4040B.EnabIed = 0 Cmd400B.EnabIed = 1 End If End Sub Private Sub Cmd4040C_ClickO Check40C.Enabled = 0 PortType% = PortNum% BitNum% = 4 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.VaIue = I End Sub Private Sub Cmd4040C_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value = 1 LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data pomts to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If VlemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HfghChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory b u ^ r set up by Windows to an arr^ for use by Visual Basic ULStat% = cbWmBufFoAtray%(MemHandl^^ ADData%(0), FirstPomt&, CBCount&) 233 If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(L%) + 0 End If Print #I,i Nexti% Beep PortType% = PortNuin% BitNum% = 4 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.VaIue = 0 ChkLEDoff.Value = I Cmd4040C.EnabIed = 0 Cmd400C.Enabled = I End If End Sub Private Sub CmdAI I OOA CIickQ CheckAIIOA.EnabIed = 0 PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBItOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDoiu Value = I End Sub Private Sub CmdAIIOOA_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) IfButton = 2Then ChkButton.VaIue = I LowChan%=0 ' first channel to acqttûre (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount&= (NtnnPomts&) ' total number of data pomts to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options»/» = NOCONVERTDATA * use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS 'set the gam 234 If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Optfons%) If ULStat% = 30 Then R^gBox "Change the Gam% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data Gom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandle%, ADData%(0), F&rstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then ] = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoffValue = I CmdAI lOOAÆnabled = 0 CheckAIIOB.EnabIed= I End If End Sub Private Sub CmdAI lOOB ClickQ CheckAI I OB.Enabled = 0 PortType% = PortNum% Bi^um% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.Value = I End Sub 235 Private Sub CmdAIIOOB_MouseOown(Buttoa As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.Value = I LowChan% = 0 ' ftrst channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5VOLTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then f^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPointA, CBCountA) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then i = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon.VaIue = 0 ChkButtotLValue = 0 ChkLEDoffValue = I CmdAI 100B.Enabled = 0 CheckAIIOCÆnabled = I End If End Sub Private Sub CmdAIIQOCjCückO CheckAIIOC.Enabled=0 236 PortType% = PortNum% BitNum% = 0 BitVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BttNum%, BitVaIue%) If ULStal% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = I End Sub Private Sub CmdAJ100C_MouseDovm(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ' set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufToArray%(MemHandIe%, ADData%(0), FirstPomt&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then i = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PorfType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNian%, BitVaIue%) 237 If ULStat% o 0 Then Stop ChkLEDon-Value=0 ChkButton. Value=0 ChkLEDoff.Value = I CmdAIIOOC.EnabIed = 0 End If End Sub Private Sub CmdAI200A_CIickO CheckAJ20A.EnabIed = 0 PortType% = PortNum% BitNum% = 0 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVatue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.Value = I End Sub Wvate Sub CmdAI200A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I 'last channel to acquire (vertical) CBCount& = (NumPomts&) ' total number of data points to collect (see General Code) CBRate& = 500 ’ sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandIe% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, NfemHandle%, Options%) IfULStat94 = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported pin" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cb WihBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = GTo 1999 If ADData“/o(i%) < 0 Then j = ADData%(i%) + 65536 Else 238 j = ADData%(i%) + 0 End If Print #I,j Next i% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNiun, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.Value = 0 ChkLEDoffValue = 1 CmdAI200A.EnabIed = 0 CheckAOOBJEnabled = I End If End Sub Private Sub CmdAI200B_CIickO CheckAI20B.EnabIed = 0 PortType% = PortNum% BitNum% = 0 BttVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BrtVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon.VaIue = I End Sub Private Sub CmdAI200B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' fûst channel to acquire (horizontal) HighChan% = I ' last channel to acqune (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 'sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gam% = BIP5VOLTS ' set the gam If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% =cbAInScan%(BoardNum%, LowCban%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, 239 "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' ' Transfer the data from the memory buffer set up by Wmdows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut“/o(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.VaIue = 0 ChkButton. Value = 0 ChkLEDoff;VaIue= I CmdAI200B.EnabIed = 0 CheckAI20C.EnabIed = I End If End Sub Private Sub CmdAI200C_CIickO CheckAI20C.Enabted = 0 PortType% = PortNum% BitNum% = 0 BitValue% = 1 ULStat% = cbOBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDoiuValue = I End Sub Private Sub CmdAI200C_MouseDown(Button As Integer, Shift As Integer, X As Single^ Y As Single) IfButton=2Then ChkButton.VaIue= I 240 LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of points to collect (see General Code) CBRate& = 500 ' sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BEP5V0LTS ' set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.”, 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.Value = 0 ChkLEDoff.Value= I CmdA1200CÆnabled = 0 End If End Sub Prwate Sub CmdAI300A_ClickO CheckAISOAÆhabled=0 PortType% = PortNum% BhNum%=0 BftValue% = 1 ULStat% = cbDBAOut%(BoardNum^ PortType%, BitNum%, BitValue%) 241 If ULStal% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = I End Sub Private Sub CmdAI300A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton.VaIue = 1 LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ’ last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 ' samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gatn% = B1P5V0LTS ’ set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then R^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data from the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop For i% = 0 To 1999 If ADData%(i%) < 0 Then J = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #1,] Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue%=0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value=0 ChkButton.VaIue=0 ChkLEDoffValue = I CmdAI300A.5iabIed=0 242 CheckAJ30B.EnabIed = I End If End Sub Private Sub CmdADOOBjCIickO CheckAOOB-Enabled = 0 PortType% = PortNum% BitNum% = 0 BitVaiue% = 1 ULStat% = cbDBitOut%(BoardNuin, PortType%, BItNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoff.Value = 0 ChkLEDon. Value = I End Sub Private Sub CmdAI300B_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRate& = 500 'sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory bufter set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandle%, ADData%(0), FftstPointA, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep 243 PortType% = PortNum% BitNum% = 0 BitValue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%» BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoff.VaIue= I CmdAI300B.Enabled = 0 CheckAI30C.Enabled = I End If End Sub Private Sub CmdAlSOOCjClickO CheckAI30C.Enabled = 0 PortType% = PortNum% BitNum% = 0 BitValue% = 1 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BltValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = 1 End Sub Private Sub CmdAUOOC_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ first channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data pomts to collect (see General Code) CBRate& = SOO 'samplmg rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if using 16 bit board Gain% = B1P5V0LTS ’ set the gain If MemHandle% = 0 Then Stop ' check that a handle to a memory bufter exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandl^, Optioos%) If ULStat% = 30 Then MsgBox "Chan^ the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory bufter set up by Wmdows to an amy for use by Visual Basic 244 ULStat% = cbWmBufroArray%(MemHandIe%, ADData%(0), FirstPomt&, CBCount&) If ULStat% o 0 Thea Stop Fori% = 0Tol999 If ADData%(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #l,j Next i% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBttOut%(BoardNunu PortType%, BttNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton. Value = 0 ChkLEDoffValue = I CmdAI300C£nabled = 0 End If End Sub Private Sub CmdAI400A_ClickO CheckAI40A.Enabled = 0 PortType% = PortNum% BltNum% = 0 BitValue% = 1 ULStat% = cbDBitOut%(BoardNunu PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDoffValue = 0 ChkLEDon. Value = I End Sub Private Sub CmdAI400A_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquhe (vertical) CBCount& = (NumPomts&) ’ total number of data points to collect (see General Code) CBRate&=500 'samplmg rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gam% = BIP5V0LTS set the gam 245 If MemHandIe% = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAInScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data &om the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufroArray%(MemHandIe%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData“/o(i%) < 0 Then j = ADData%(i%) + 65536 Else j = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Then Stop ChkLEDon.Value = 0 ChkButton. Value = 0 ChkLEDoff.Value = 1 CmdAI400A.Enabled = 0 CheckAI40B.Enabled = I End If End Sub Private Sub CmdAJ400BjClickO CheckAI40B.Enabled = 0 PortType% = PortNum% BitKum% = 0 BhVaIue% = I ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValud^) If ULStat% o 0 Then Stop ChkLEDoffValue=0 ChkLEDon. Value = I End Sub 246 Private Sub CmdAI400B_MouseDown(Buttoa As Integer, Shift As Integer, X As Single, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ’ftrst channel to acquire (horizontal) HighChan% = 1 ' last channel to acquire (vertical) CBCount& = (NumPomts&) ’ total number of data points to collect (see General Code) CBRate& = SOO 'sampling rate (samples per second) Options% = NOCONVERTDATA ’ use NOCONVERTDATA if using 16 bit board Gain% = BCP5V0LTS ' set the gain If MemHandleVo = 0 Then Stop ’ check that a handle to a memory buffer exists ULStat% = cbAlnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandle%, Options%) If ULStat% = 30 Then A^gBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gam" If ULStat% o 0 And ULStat% o 91 Then Stop ' Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWinBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) <0 Then j = ADData%(i%) + 65536 Else j = ADData*/o(i%) + 0 End If Print #l,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitValue% =0 ULStat% = cbDBitOut%(BoardNum, PortType%, BitNum%, BitValue%) If ULStat% o 0 Then Stop ChkLEDon. Value = 0 ChkButton.Value = 0 ChkLEDoffValue = 1 CmdAI400B.Enabled = 0 CheckAI40C.Enabled = 1 End If End Sub Private Sub CmdAI400C_ClickQ CheckAI40C.EnabIed = 0 247 PortType% = PortNum% BitNum% = 0 BitValue% = I ULStat% = cfaDBftOut%(BoardNuin, PortType%, BitNum%, BitVaIue%) If ULStat% o 0 Thea Stop ChkLEDoff.VaIue = 0 ChkLEDon.Value = I End Sub Private Sub CmdAI400C_MouseDown(Button As Integer, Shift As Integer, X As Smgle, Y As Single) If Button = 2 Then ChkButton. Value = I LowChan% = 0 ' first channel to acquire (horizontal) HighChan% = I ' last channel to acquire (vertical) CBCount& = (NumPoints&) ' total number of data points to collect (see General Code) CBRateA = 500 'sampling rate (samples per second) Options% = NOCONVERTDATA ' use NOCONVERTDATA if usmg 16 bit board Gain% = BIP5V0LTS ’ set the gain If MemHandIe% = 0 Then Stop ' check that a handle to a memory buffer exists ULStat% = cbAJnScan%(BoardNum%, LowChan%, HighChan%, CBCount&, CBRate&, Gain%, MemHandIe%, Options%) If ULStat% = 30 Then MsgBox "Change the Gain% argument to one supported by this board.", 0, "Unsupported gain" If ULStat% o 0 And ULStat% o 91 Then Stop ’ Transfer the data ftom the memory buffer set up by Windows to an array for use by Visual Basic ULStat% = cbWmBufToArray%(MemHandle%, ADData%(0), FirstPoint&, CBCount&) If ULStat% o 0 Then Stop Fori% = OTo 1999 If ADData%(i%) < 0 Then i = ADData%(i%) + 65536 Else ] = ADData%(i%) + 0 End If Print #I,j Nexti% Beep PortType% = PortNum% BitNum% = 0 BitVaIue% = 0 ULStat% = cbDBitOut%(BoardNmn, PortType%, BitNum%, BitVaIue%) 248 If ULStat% o 0 Then Stop ChkLEDon-Value = 0 ChkButton. Value=0 ChkLEDoffValue = I CmdAI400C.Enabted = 0 End If End Sub Private Sub CmdExitjCIickO ULStat% = cbWmBufFree%(MemHandIe%) If ULStat% o 0 Then Stop DataValueS = 0 ULStat% - cbDOut%(BoardNum, PortNum%, OataValue%) If ULStat% o 0 Then Stop Close#! End End Sub Private Sub CmdSavejCIickQ Open PhDFUe For Output As #l CmdSaveÆnabled = 0 PhDFileÆnabled = 0 CmdOOA.EnabIed = I End Sub Private Sub Form LoadQ 'Declare revision level of Universal Library ULStat% = cbDeclareRevision(CURRENTREVNUM) Initiate error handling 'Activating error handling will trap errors like 'bad channel numbers and non-configured conditions. 'Parameters: ’ PRINTALL :all warnings and errors encountered will be printed ' DONTSTOP rifan error is encountered, the program wül not stop, ' errors must be handled locally ULStat% = cbErrHandImg%(PRINTALL, DONTSTOP) If ULStat% o 0 Then Stop Tf cbErrHandImg% is set fbr STOPALL or STOPFATAL during the program 'design stage. Visual Basic will be unloaded when an error B encountered. 'We suggest trappmg errors locally until the program is reacfy for compQmg to avoid losmg unsaved data durmg program desigL This can be done by settmg cb&rHandlmg options as above and checkmg the value of ULStat% 'after a call to the library. If it is not equal to 0, an error has occurred. 249 MemHandIe% = cbWmBu£^oc%(NumPomts&) 'Set aside memory to hold data If MemHandle%=0 Then Stop ULStat% = cbDConfigPort%(BoardNum, PortNum%, Direction%) 'Configure Port A If ULStat% o 0 Then Stop ULStat% = cbDConfigPort%(BoardNum, PortNum2%, Direction%) 'Configure Port B If ULStat% o 0 Then Stop ChkLEDoff. Value = I End Sub 250 APPENDIX C SLIPPAGE PLOTS 251 80 60 40 2 0 0 -20 -40 -60 -80 -100 0 2 010 30 40 E y e R o t a t io n a n g l e (deg rees ) SLIPPAGE PLOT 1: Measured search coil slippage for each nasal eye rotation angle in Subject I are represented by solid circles. The best tit non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements* respectively. 252 80 60 40 2 0 0 -20 -40 -60 -80 -100 1 00 2 0 30 40 E y e R o t a t io n A n g l e (degrees ) SLIPPAGE PLOT 2: Measured search coil slippage for each nasal eye rotation angle in Subject 2 are represented by solid circles. The best fit non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements, respectively. 253 ^ 60 i - I « I Icd . 0 u % d -40 s X - 6 0 M -80 % -100 0 1 0 2 0 30 40 E y e Ro ta tio n An g le (degrees ) SLIPPAGE PLOT 3: Measured search coil slippage for each nasal eye rotation angle in Subject 3 are represented by solid circles. The best fît non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements, respectively. 254 80 60 40 u 2 0 0 -20 -40 -60 -80 -100 0 1 0 2 0 30 40 E y e Ro ta tio n a n g l e (degrees ) SLIPPAGE PLOT 4: Measured search coil slippage for each nasal eye rotation angle in Subject 4 are represented by solid circles. The best fit non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements^ respectively. 255 ^ 60 < ° "O g 20 i Iu «0 % d -40 8 X -60 ' i u -80 50 -100 0 0 2 001 30 40 E y e Ro ta tio n A n g l e (degrees ) SLIPPAGE PLOT 5: Measured search coil slippage for each nasal eye rotation angle in Subject 5 are represented by solid circles. The best fît non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements» respectively. 256 80 60 < El. 0 40 ; 3 5 2 0 ë Gd 0 1 -20 co3 -40 8 X -60 < Cd -80 % -100 0 1 0 2 0 30 40 Eye Ro ta tio n An g l e (degrees ) SLIPPAGE PLOT 6 : Measured search coil slippage for each nasal eye rotation angle in Subject 6 are represented by solid circles. The best fit non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements, respectively. 257 u oc 60 < o 40 S 3 Z U 0 t . à -40 8 X -60 ceBd 6 0 -100 - 0 1 0 2 0 30 40 Eye Ro ta tio n A n g le (degrees ) SLIPPAGE PLOT 7: Measured search coil slippage fiir each nasal eye rotation angle in. Subject 7 are represented by solid circles. The best fit non-linear regression of the data is also shown. Positive and negative slippage values indicate temporal and nasal search coil displacements, respectively. 258 APPENDIX D GAZEPLOTS 259 BD E I è -60 r ----- i -80 -100 0 1 2 T im e (sec o n d s ) GAZE PLOT 1; Eye position relative to the LED target center for Subject 1 while gazing straight-ahead. This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. BD E £ I ■«» -100 0 1 0 1 2 0 1 22 Time (seconds) GAZE PLOT 2; Eye position relative to the LED target center for Subject 2 while gazing straight-ahead. This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. BDE 80 60 40 - - - ■■ ------ è 2 0 0 —- I -20 -40 -60 - - ...... —...... " g -80 -100 r 0 1 2 ...... -.. T im e (seconds ) GAZE PLOT 3; Eye position relative to the LED target center for Subject 3 while gazing straight-ahead. This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. BD E B s -100 0 1 2 T im e (seconds ) GAZE PLOT 4; Eye position relative to the LED target center for Subject 4 while gazing straight-ahead. This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively), Positive and negative position values indicate gaze undershoots and overshoots, respectively. B D E 80 60 y 40 è 2 0 1 0 o ...... - 2 0 1 -40 a -60 -—...... —* ■— — — ...... -...... - - -80 - 1 0 0 0 1 2 1 T im e (seconds ) GAZE PLOT S; Eye position relative to the LED target center for Subject 5 while gazing straight-ahead. This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B D Ë 60 ------^ I - ■ - ■ ■■ ...... * è s c -20 - ..... - - ' —------— g -40 g -eo -...... ■ -...... ------g -80 -100 2 0 1 2 1 0 1 2 T im e (seconds) GAZE PLOT 6: Eye position relative to the LED target center for Subject 6 while gazing straight-ahead, This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. BDE 80 60 40 i è 2 0 0 i -20 -40 -60 ï -80 -100 2 T im e (seconds ) GAZE PLOT 7; Eye position relative to the LED target center for Subject 7 while gazing straight-ahead, This data collection occurred during five separate 2-second trials (represented by A, B, C, D and E, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 è g g -20 I B -60 § -80 -100 0.0 0.5 1.0 1.5 2.0 0 . 0 0.5 1 . 0 1.5 2.0 T im e (seconds ) GAZE PLOT 8; Eye position relative to the LED target center for Subject 1 while gazing 10® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è gI 4■“ 0 E ■«“ -80 -100 0 . 0 0 . 6 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds) GAZE PLOT 9; Eye position relative to the LED target center for Subject2 while gazing 10“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 40 i ë 2 0 0 § - 2 0 g -40 g -60 g -80 -100 1------1------1------1------1------1------0 0 . 6 1 . 0 1.5 2 . 0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 10; Eye position relative to the LED target center for Subject 3 while gazing 10® left, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 g 40 è 20 1 0 % p -20 S -40 -60 § a -80 -100 —I— —I— Ï 0,0 0,5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 11: Eye position relative to the LED target center for Subject 4 while gazing 10® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B ...... — ...... -...... —....— y è § - ' ■ ■■ ■■ - ...... -...... ------ - ...... - I I 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 12; Eye position relative to the LED target center for Subject 5 while gazing 10® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è 4*"' »>" I g H 1------1------1------0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 13; Eye position relative to the LED target center for Subject 6 while gazing 10“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è s K '20 I I -eo S .80 -100 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 14: Eye position relative to the LED target center for Subject 7 while gazing 10® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 2 0 I - I -80 g -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 15; Eye position relative to the LED target center for Subject 1 while gazing 20“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 60 è _J ------ s -80 -100 1------1------1------ 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T ime (seconds) GAZE PLOT 16; Eye position relative to the LED target center for Subject 2 while gazing 20“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 40 è 2 0 «WWW#* 0 § - 2 0 £ -40 a -60 g -80 -100 I I —I— 1------1------1------0 . 0.5 1 . 0 1.5 2 . 0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 17: Eye position relative to the LED target center for Subject 3 while gazing 20“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è I " g I -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 18; Eye position relative to the LED target center for Subject 4 while gazing 20" left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 y 40 2 0 0 1 i# ii I' z E - 2 0 -40 g -60 s -80 - 1 0 0 1------1------1------—I —I— —I— 0 0,5 1.0 1.5 2 0 . 0 0.5 1 . 0 1.5 2 . 0 Time (seco n d s) GAZE PLOT 19; Eye position relative to the LED target center for Subject 5 while gazing 20" left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 8 0 60 40 è 2 0 0 g - 2 0 I ■40 -60 g -80 -100 1------1------1------0 0 0,5 1.0 1.5 2.0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 20; Eye position relative to the LED target center for Subject 6 while gazing 20® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B g C -20 S -40 I -80 g -80 -100 0 , 0 0,5 1 , 0 1.5 2 . 0 0 , 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds) GAZE PLOT 21: Eye position relative to the LED target center for Subject 7 while gazing 20® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è I ■” £ -40 B - 0 0 •80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 22; Eye position relative to the LED target center for Subject 1 while gazing 30® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds) GAZE PLOT 23; Eye position relative to the LED target center for Subject 2 while gazing 30“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 40 è 2 0 0 I - 2 0 I -40 g -60 8 -80 -100 I I I------ 0 0 0.5 1.0 1.5 2.0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 24; Eye position relative to the LED target center for Subject 3 while gazing 30" left, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è S -*o ^ -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 25; Eye position relative to the LED target center for Subject 4 while gazing 30” left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B 80 è g -100 0 . 0 0,5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 26; Eye position relative to the LED target center for Subject 5 while gazing 30“ left, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B II - B ■«> g -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) (GAZE PLOT 27; Eye position relative to the LED target center for Subject 6 while gazing 30“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è s Ig -20 - ^ -60 § -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 28; Eye position relative to the LED target center for Subject 7 while gazing 30® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 5 S -20 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 29; Eye position relative to the LED target center for Subject 1 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively), Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B g -80 -100 1------1------1------ 0 . 0 0.5 1 . 0 1.5 2 . 0 0.0 0.5 1.0 1.5 2.0 T im e (seconds) GAZE PLOT 30; Eye position relative to the LED target center for Subject 2 while gazing 40“ left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 40 ë 2 0 0 § - 2 0 2 -40 S -60 g -80 -100 — ,— I —I— 1 1 1 — 0 0 . 6 1 . 0 1 . 6 2 . 0 0.0 0.6 1.0 1.6 2.0 T im e (seconds ) GAZE PLOT 31; Eye position relative to the LED target center for Subject 3 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively), Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 60 - - — ...... —...... —...- I è - ...... ------....-■ ...... s I -20 ...... g - I •«> ...... ------80 -100 - ■ ...... - ...... — T 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 32: Eye position relative to the LED target center for Subject 4 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è g -80 -100 1------1------1------0 . 0 0.5 1 . 0 1.5 2 . 0 0.0 0.5 1.0 1.5 2.0 T im e (seconds) GAZE PLOT 33; Eye position relative to the LED target center for Subject 5 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 8 0 60 40 2 0 0 § - 2 0 pk -40 -60 g g -80 -100 I P I 1------1------1------0 0 0 . 6 1 . 0 1.5 2 0.0 0.6 1.0 1.6 2.0 T im e (seconds) GAZE PLOT 34: Eye position relative to the LED target center for Subject 6 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 y 40 ê 2 0 1 0 z o - 2 0 s -40 -60 g -80 - 1 0 0 —I— —I— —I— 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 35; Eye position relative to the LED target center for Subject 7 while gazing 40® left. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B ë S S -20 g -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 36; Eye position relative to the LED target center for Subject 1 while gazing 10® left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B S c -20 g -80 -100 —I— —I— —1— 0 . 0 0 . 6 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 37; Eye position relative to the LED target center for Subject 2 while gazing 10“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 g 40 % è 2 0 1 0 % o - 2 0 1 4 0 -60 1 g -80 - 1 0 0 1------1------1------1------1------1------0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 38; Eye position relative to the LED target center for Subject 3 while gazing 10“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B ë g I -20- E -«o 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 39: Eye position relative to the LED target center for Subject4 while gazing 10“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B 8 0 60 —...... —...... - 40 § & 2 0 - 0 H\i iVi f Mlïfri- 0 Yi ***■»* - 2 0 I -40 s -60 ...... -- -.— ...... - ..... - - - g -80 -100 1 1 1 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 40; Eye position relative to the LED target center for Subject 5 while gazing 10® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B ë £ w I -80 o -80 -100 1------1------1------ 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 41; Eye position relative to the LED target center for Subject 6 while gazing 10“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B I è g Ig -20 - u> H •«> o -80 -100 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 42; Eye position relative to the LED target center for Subject 7 while gazing 10" left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B I è s # # * ###' IC --20 E ■«> -80 -100 -1— — 1— 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 43; Eye position relative to the LED target center for Subject I while gazing 20® left with afterimage Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B è g II -20- E -«o wo -80 -100 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 44; Eye position relative to the LED target center for Subject 2 while gazing 20® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 8 0 60 40 2 0 0 -20 I -40 w s ■60 S -80 -100 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 45; Eye position relative to the LED target center for Subject 3 while gazing 20" left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è II --20 I -80 s -80 -100 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 46: Eye position relative to the LED target center for Subject 4 while gazing 20® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A B è «fW. I -20 %w w g -80 -100 1------1------1------0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 47; Eye position relative to the LED target center for Subject 5 while gazing 20® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B s II --20 E - « 0 -100 0 . 0 0,5 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 48; Eye position relative to the LED target center for Subject 6 while gazing 20" left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively), Positive and negative position values indicate gaze undershoots and overshoots, respectively. B I è g Ig -20 - w I -80 s -100 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 49: Eye position relative to the LED target center for Subject 7 while gazing 20® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 60 I II --20 I -80 s -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T ime (seconds ) GAZE PLOT SO; Eye position relative to the LED target center for Subject 1 while gazing 30® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è j ------ s Ig ^0-20 w E -e® Oh-> -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT SI; Eye position relative to the LED target center for Subject 2 while gazing 30® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 40 2 0 0 I - 2 0 Ph -40 w g -60 -80 -100 I —I— —I— I —I— 0 . 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 52; Eye position relative to the LED target center for Subject 3 while gazing 30® left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 8 0 60 40 è 2 0 0 - 2 0 { -40 w E -60 »—* N) -80 -100 I I I 0 0 0,5 1.0 1.5 2.0 0 . 0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 53; Eye position relative to the LED target center for Subject 4 while gazing 30® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B - ...... - .... ------■ -...... ■ ...... - I ...... è I ■ ...... - - -...— ...------ a ...... - ...... - '■ ------...... u> ...... ■■ -- -..— ■ - - ■■------...... - 0 . 0 0.5 1 . 0 1.5 2 . 0 TIME (SECONDS) GAZE PLOT 54: Eye position relative to the LED target center for Subject 5 while gazing 30** left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively), Positive and negative position values indicate gaze undershoots and overshoots, respectively, B 60 60 40 § è 2 0 0 ' 2 0 I -40 a -60 -80 -100 —I— I —I— 0 0,5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 55: Eye position relative to the LED target center for Subject 6 while gazing 30® left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 80 60 ...... — ...... - - 40 i< ## n# # <1 m>iiiiw»w»> o» m>i s 20 - - 0 -20 ------...... I -40 , .. - -60 ...... r-»w LA -80 ■100 1 “ 1 1 0 . 0 0.5 1 . 0 1.5 2.0 0.0 0.5 1 . 0 1.5 2 . 0 T im e (seconds ) GAZE PLOT 56; Eye position relative to the LED target center for Subject 7 while gazing 30“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è Ig -20 - w I—* -80 -100 0 . 0 0.5 1 . 0 1.5 2 . 0 0 . 0 0.5 1 . 0 1.5 2.0 T im e (seconds) GAZE PLOT 57: Eye position relative to the LED target center for Subject 1 while gazing 40“ left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B è I ■” s ^0 t—tw I ■“ ^4 >80 -100 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 58: Eye position relative to the LED target center for Subject 2 while gazing 40“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. A " Wm, A# 1 ■” 2 B ■«“ 90 .80 -100 T------1------r 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T im e (seconds ) GAZE PLOT 59: Eye position relative to the LED target center for Subject 3 while gazing 40“ left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B I è 20 S IG --20 w* B vo -80 -100 0.0 0,5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 T im e (seconds) GAZE PLOT 60; Eye position relative to the LED target center for Subject 4 while gazing 40“ left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 8 0 60 40 I ê 20 0 (nniwwiii» m u *1 fil *1 # » I. li ' ' ' % I « I, M l'i" ' ^ I -20 Ai -40 g -60 § -80 -100 1------1------1------1------1------1------0 0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 61; Eye position relative to the LED target center for Subject 5 while gazing 40" left with afterimage, Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 60 I ê g Ig -20 - NJ -80 -100 1------1------1------0,0 0,5 1,0 1.5 2.0 0.0 0,5 1,0 1,5 2,0 TIME (SECONDS) GAZE PLOT 62; Eye position relative to the LED target center for Subject 6 while gazing 40“ left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. B 60 w# è g B ' 2 0 B •80 -100 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 TIME (SECONDS) GAZE PLOT 63; Eye position relative to the LED target center for Subject 7 while gazing 40" left with afterimage. Data collection occurred during two separate 2-second trials (represented by A and B, respectively). Positive and negative position values indicate gaze undershoots and overshoots, respectively. LIST OF REFERENCES 1. Cline D, Hofstetter H, GrifBn J. Dictinnarv of visual science 1989. Radnor, Pennsylvania:Chilton Trade Book Publishing. 2. BCrauskopf J, Comsweet TN, Riggs LA. Analysis o f eye movements during monocular and binocular fixation. JOpt Soc Am 1960;50:572-8. 3. Comsweet TN. Determination of the stimuli for involuntary drifts and saccadic eye movements. J Opt Soc Am 1956;46:987. 4. Hart W. Adler^s phvsioloev of the eve 1992;chap5:101 -97. St LouisrMosby Year Book. 5. Ciuffieda KJ, Tannen B. Eve movement basics for the clinician 1995;chap2:10-35. 6 . Leigh RJ, Zee DS. 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