Scheiwiller, Peter Michael; (1992) The effects of display flicker on visual performance and the applications of stereoscopic television. Doctoral thesis (Ph.D.), Institute of Ophthalmology.

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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.

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