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Characteristics of Optokinetic Torsion in Upright and Supine Orientations

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Characteristics of Optokinetic Torsion in Upright and Supine Orientations CHARACTERISTICS OF OPTOKINETIC TORSION IN UPRIGHT AND SUPINE ORIENTATIONS by ARTHUR REMY MALAN S.B. Aeronautics and Astronautics, M.I.T. (1983) Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN AERONAUTICS AND ASTRONAUTICS at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June, 1985 © Massachusetts Institute of Technology, 1985 A I Signature of Author Department of Aeronautics and Astronautics May 16, 1985 Certified by . ofessor Robert V. Kenyon IT sis Supervisor Accepted by Professor Harold Y. Wachman Chairman Departmental Graduate Committee 2 CHARACTERISTICS OF OPTOKINETIC TORSION IN UPRIGHT AND SUPINE ORIENTATIONS by ARTHUR REMY MALAN Submitted to the Department of Aeronautics and Astronautics on May 16, 1985 in partial fulfillment of the requirements for the Degree of Master of Science in Aeronautics and Astronautics ABSTRACT An instrument to measure torsion by the magnetic search coil method was built. A torsion coil was developed that could be mounted on a soft contact lens. The coil was relatively comfortable to wear. System noise without lowpass filtering was 0.125*. Post- processing with a digital filter reduced noise to 0.025*. Two subjects were tested in both the upright and supine positions. A wide angle optokinetic drum rotating at speeds up to 30*/sec was used to induce torsion. Torsion saccades are depressed with respect to horizontal and vertical saccades. The torsion main sequence slope (saccade peak velocity vs. saccade amplitude) produced by a log-log straight line fit was found to be greater in the supine position than in the upright position for both subjects. The ratio of torsion slow phase velocity to stimulus velocity was on the order of 0.1. Torsion nystagmus is symmetric with respect to intorsion and extorsion. No obvious correlation exists between torsion and circularvection. A 2*-3* d.c. torsion offset was noted for upright positions but not for supine positions. Both subjects noted adaptation effects to the stimulus and residual torsion was observed after the termination of stimulus. Thesis Supervisor: Professor Robert V. Kenyon Title: Assistant Professor of Aeronautics and Astronautics 3 ACKNOWLEDGEMENTS There is an endless list of people to thank for their useful contributions to this project. In particular, I would like to thank the following: Professor Robert V. Kenyon, for his willingness to subject himself to the trials of experimentation and for his useful comments during the preparation of this thesis. Jay Cohan, whose dedication and enthusiasm played a major role throughout the project. For building parts and analyzing data and reviewing this thesis, I owe him a great deal indeed. Sherry Modestino, Bob Renshaw, and Marilyn Williams, who kept the Man-Vehicle Laboratory running amidst all the daily confusion involved with this and a score of other projects. Finally, but far from least, I would like to thank my wife for her patience and understanding during the course of this project. Her devotion and love made the intolerable tolerable. 4 TABLE OF CONTENTS CHAPTER 1 INTRODUCTION 10 1.1 Torsion 10 1.2 Measuring Torsion by the Search Coil Method 12 CHAPTER 2 INSTRUMENT 14 2.1 Principles Behind the Search Coil Technique 14 2.2 Instrument Electronics 16 2.2.1 Timing Generator 18 2.2.2 Magnetic Field Drivers 21 2.2.3 Input Signal Demodulator 21 2.2.4 Power Supplies and Construction Methods 24 2.3 Physical Apparatus 26 2.3.1 The Cube 27 2.3.2 The Frame 27 2.3.3 Magnetic Field Coils 30 2.3.4 Bite Board Assembly 31 2.3.5 Optokinetic Drum and Motor Assembly 31 CHAPTER 3 TORSION COIL 38 3.1 Creating the Coil 40 3.2 Soft Contact Lens Preparation 40 5 3.3 Mounting the Coil on the Lens 41 3.4 Calibration 42 3.5 Subject Instrumentation 44 CHAPTER 4 EXPERIMENTAL PROCEDURES 48 4.1 Upright Experiment 48 4.2 Supine Experiment 51 4.3 Delay Between OKN Drum Runs 53 CHAPTER 5 DATA ANALYSIS 54 5.1 Data Filtering 54 5.2 Torsion Main Sequence Analysis 57 5.3 Slow Phase Velocity Analysis 60 CHAPTER 6 RESULTS 61 6.1 Torsion Main Sequence 61 6.1.1 Least Squares Fit 66 6.1.2 Confidence Intervals of the 67 Main Sequence Slopes 6.2 Torsion Slow Phase Velocity 68 6.3 Correlation between Circularvection and Torsion 73 6.4 Some Observations 73 CHAPTER 7 CONCLUSIONS 76 7.1 Torsion Main Sequence Summary 76 7.2 Main Sequence: Torsion versus HorizontalNertical 77 6 7.3 Torsion Slow Phase Velocity Summary 79 7.4 Torsion and Circularvection 80 APPENDIX A PICTORIAL GUIDE TO TORSION COIL 81 AND LENS ASSEMBLY APPENDIX B RAW DATA AND OKN DRUM SPEEDS 84 B.1 Raw Data Figures 84 B.2 Actual OKN Drum Speeds 84 APPENDIX C SOFTWARE LISTINGS 92 C.1 A 31-Point FIR Filter: ifilt.c 92 C.2 A 99-Point FIR Filter: filt99.c 92 C.2 A Data Decimation Program: shrink.c 93 APPENDIX D SUGGESTIONS FOR THE 117 MAN-VEHICLE LABORATORY D.1 Discussion of the Torsion Instrument 117 D.2 Suggestions for Future Research 118 REFERENCES 119 7 TABLE OF FIGURES Figure Page 2.2 Electronics Block Diagram 17 2.2.1 Timing Generator 19 2.2.2 Magnetic Field Driver 22 2.2.3.1 Demodulator Input Stage 23 2.2.3.2 Analog Mulitplexer and Output Stage 25 2.3.1 Wooden Cube 28 2.3.2 Wooden Frame 29 2.3.4.1 Side View of Bite Board Assembly 32 2.3.4.2 Plexiglas Bite Board 33 2.3.4.3 Side View of Physical Apparatus 34 2.3.5.1 Motor and Tachometer Switching Schematic 36 2.3.5.2 Optical Tachometer 37 3.0 Torsion Coil and Contact Lens (Top View) 39 3.4 Torsion Calibrator and Linearity Curve 43 3.5 Cheek Instrumentation 46 5.1 Typical Torsion and Velocity Sequence 56 6.1.1 Main Sequence - Subject A Upright Intorsion Stimulus 62 6.1.2 Main Sequence - Subject A Upright Extorsion Stimulus 62 6.1.3 Main Sequence - Subject A Supine Intorsion Stimulus 63 6.1.4 Main Sequence - Subject A Supine Extorsion Stimulus 63 6.1.5 Main Sequence - Subject B Upright Intorsion Stimulus 64 8 6.1.6 Main Sequence - Subject B Upright Extorsion Stimulus 64 6.1.7 Main Sequence - Subject B Supine Intorsion Stimulus 65 6.1.8 Main Sequence - Subject B Supine Extorsion Stimulus 65 6.2.1 SPV - Subject A Upright Intorsion Stimulus 69 6.2.2 SPV - Subject A Upright Extorsion Stimulus 69 6.2.3 SPV - Subject A Supine Intorsion Stimulus 70 6.2.4 SPV - Subject A Supine Extorsion Stimulus 70 6.2.5 SPV - Subject B Upright Intorsion Stimulus 71 6.2.6 SPV - Subject B Upright Extorsion Stimulus 71 6.2.7 SPV - Subject B Supine Intorsion Stimulus 72 6.2.8 SPV - Subject B Supine Extorsion Stimulus 72 6.4 Residual Torsion in Subject B 74 7.2 Main Sequences - Torsion and Horizontal 78 A.1 Lens Preparation 82 A.2 Assembling and Mounting Torsion Coil 83 B.1 Subject B Upright Intorsion Stimulus 85 B.2 Subject B Upright Intorsion Stimulus 86 B.3 Subject A Supine Extorsion Stimulus 87 B.4 Subject A Supine Intorsion Stimulus 88 B.5 Subject B Supine Intorsion Stimulus 89 C.1 Power Spectrum of ifilt.c 94 C.2 Power Spectrum of filt99.c 94 9 TABLE OF TABLES 4.1 Upright Torsion Experiment 50 Stimulus Presentation Sequences 4.2 Supine Torsion Experiment 52 Stimulus Presentation Sequences 6.1.1 Least Squares Straight Line Fit for 66 log(Peak Velocity) vs. log(Amplitude) 6.1.2 Confidence Intervals of the Slope 67 of the Main Sequence Fit 6.2 Slow Phase Velocity Mean Gain 68 B.2.1 Upright Torsion Experiment Desired and 90 Actual Drum Speeds B.2.2 Supine Torsion Experiment Desired and 91 Actual Drum Speeds 10 CHAPTER 1 INTRODUCTION This thesis describes the development of and the experimentation with an instrument for measuring torsion. Torsion is the rotation of the eye about the visual axis or the line of sight. The study of torsion and how it arises is important to the understanding visual-vestibular interaction and the perception of the body's physical orientation. Traditionally, most eye movement research has concentrated upon horizontal and vertical eye movements. Horizontal and vertical eye movements have been easier to measure (e.g. via EOG) than torsion and have been well categorized in the literature. For torsion there is a dearth of published information available. For example, to the best of the author's knowledge, no study examing saccadic torsion for a normal, untrained human has ever been published prior to this thesis. 1.1 Torsion Torsion has been had a history of diverse nomenclature; synonyms for torsion include cyclotorsion, cyclo-duction and ocular counterrolling (OCR). Torsion is essentially an involuntary reaction in untrained normal human subjects that occurs in response to visual and vestibular stimuli [Dichgans and Brandt, 1973; Crites, 1980]. The major problem with torsion is the difficulty of precisely measuring 11 it. Various torsion measuring strategies have been tried and four primary methods have been identified in the literature. These methods are the alignment of after-images [Balliet and Nakayama, 1978], measurement by photographic means [Miller, 1962; Balliet and Nakayama, 1978; Lichtenberg, 1979], the reflection of light from the eye or a lens [Kertesz and Jones, 1969; Petrov and Zenkin, 1973], and direct measurement by the use of a search coil in a magnetic field [Robinson, 1963; McElligott et. al., 1979]. The first method, after-image alignment, is a totally subjective measurement that subjects provide by, typically, aligning a bar to the same angle of rotation as an after image on their retinae.
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