The effects of display flicker on visual performance, and^om^ applications of stereoscopic television. Thesis submitted for the degree of Doctor of Philosophy in Biophysics of the University of London. Peter Michael Scheiwiller B.A. (Cantab) Department of Visual Science Institute of Ophthalmology University of London , ------- Judd Street o n a o London W C1H 9Q S sjREEi June 1992. ProQuest Number: U063816 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest U063816 Published by ProQuest LLC(2017). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 Abstract Closed circuit television is widely used in industry for surveillance, inspection or to enable tasks to be carried out remotely because restricted space or a hazardous environment prevents man-access. Two drawbacks are (i) that cathode ray tube (CRT) displays generate an intermittently illuminated image which often appears to flicker, (ii) that with a single camera scene depth may be poorly reproduced. In book 1 guide-lines are presented for minimising display flicker. Previous research also suggests intermittent illumination may disrupt eye movements, making saccades overshoot at 50Hz but less so at higher display field rates. A proportion of saccades may be followed by corrective saccades whose almost inevitable latency may lead to a measurable difference in performance; a visually demanding task may be accomplished more quickly and possibly more accurately with a display field rate greater than 50Hz. However in this study, for visual search and reading tasks, performance was largely unaffected by display field rate. In further experiments eye movements were recorded and the distribution of saccades and fixations analysed. Saccadic overshoots followed by corrective saccades were relatively rare, but there was evidence that saccades were enlarged at 50Hz with respect to the same display at 100Hz. The lack of corrective saccades probably explained why performance was largely unaffected. In book 2 depth cues in human vision and their transmission by closed circuit television are discussed. The principles of stereoscopic television systems built by UKAEA Harwell Laboratory to improve depth perception are described. As earlier experiments have been largely equivocal about the advantages 3D TV, two new evaluations were performed, based on real applications, attempting to avoid previous pitfalls. In the first, aligning a steel plate with a rack was accomplished 17% faster with 3D TV. However in the second, little difference was found in the accuracy with which a manipulator could be positioned. This was probably due to the poor control system of the robot rather than insufficient visual feedback. Videotapes indicated a single 3D view was sufficient for both tasks. 2 Table of Contents 1. Introduction .................................................................................................................. 13 1.1 Study Aims ......................................................................................................14 1.1.1 Display Flicker............................................................................... 14 1.1.2 Stereoscopic Television .................................................................15 Book 1: Flicker 2. Basic Principles of CRT displays ..............................................................................16 2.1 Design and Construction of Display Tubes ................................................. 16 2.2 Raster Scanning and Line Interlacing ...........................................................17 2.2.1 Display Resolution ..........................................................................18 2.3 Display Phosphors..........................................................................................20 3. The Human Visual System ........................................................................................ 21 3.1 Structure of the Eye ........................................................................................21 3.1.1 Structure of the Retina ................................................................... 21 3.2 Visual Pathways to the Brain ........................................................................ 22 3.3 Response to Visual Stimuli ........................................................................... 23 3.3.1 Light and Dark Adaptation ............................................................23 3.3.2 Spectral Response ...........................................................................24 3.3.3 Spatial and Contrast Sensitivity ....................................................24 3.3.4 Visual Acuity .................................................................................. 26 3.3.5 Accommodation ..............................................................................26 4. The Perception of Flicker .......................................................................................... 27 4.1 Factors Affecting Perception of Flicker .......................................................27 4.1.1 Field size ..........................................................................................28 4.1.2 Field luminance .............................................................................. 28 4.1.3 Retinal location ...............................................................................29 4.1.4 Adapted state of the eye .................................................................29 4.1.5 Age................................................................................................... 30 4.1.6 The mark: space ratio of the flicker ..............................................30 4.1.7 The flicker waveform .....................................................................30 4.1.8 Spatial frequency ............................................................................ 30 4.2 The Effects of Line Interlacing ..................................................................... 31 4.3 Prediction of CRT Flicker from a Modulated Homogeneous Field 32 4.4 Reducing Visibility of Flicker .......................................................................34 4.4.1 Optimum Viewing Conditions .................................................... 34 3 4.4.2 Phosphor Persistence ..................................................................... 35 4.4.3 Increasing the Scan Rate ................................................................35 4.4.3.1 High scan rate cameras and monitors ........................ 35 4.4.4 Digital Signal processing.............................................................. 36 4.4.5 Alternative Scan Structures ...........................................................36 5. Movement of the Eyes .................................................................................................38 5.1 Basic types of Eye Movement ...................................................................... 38 5.1.1 Saccades ...........................................................................................39 5.1.2 Smooth Pursuit ............................................................................... 41 5.1.3 Microsaccades, Slow Drift and Tremor .......................................41 5.1.4 Vergence Movements .................................................................... 42 5.2 Recording Eye Movements ........................................................................... 43 5.2.1 Infra-Red Limbus Tracking .......................................................... 44 6. Flicker from CRT Displays and Visual Performance ......................................... 45 6.1 Fatigue and Visual Impairment .....................................................................45 6.1.1 Experimental evidence ..................................................................45 6.1.2 An etiological approach ................................................................ 46 6.1.3 Correlation and Causality ............................................................. 46 6.2 Visually Demanding Tasks ............................................................................47 7. Overview of Flicker Experiments: I. Performance ..............................................54 7.1 Apparatus .........................................................................................................55 8. Experiment 1: Visual Search ................................................................................... 58 8.1 The Task.......................................................................................................... 58 8.2 Viewing Conditions ........................................................................................59 8.2.1 Room Lighting................................................................................59 8.2.2 Viewing Distance ........................................................................... 60 8.2.3 Monitor Luminance ........................................................................60 8.3 Procedure .........................................................................................................62