Age-related changes in accommodation predict perceptual tolerance to vergence-accommodation conflicts in stereo displays
26.4017, Saturday, 16-May, 2:45 pm - 6:45 pm, Pavilion
Simon Watt1, Louise Ryan1; 1School of Psychology, Bangor University, Wales, UK
Conventional stereoscopic imagery presents conflicting stimuli to vergence and accommodation. With sufficient conflict, vergence-accommodation coupling causes inaccurate responses in one or both systems, impairing stereoscopic depth perception, or preventing it altogether. We examined tolerance of stereo depth perception to stimuli presented in-front-of and behind the screen, and examined factors that might predict it, including phoria, and decreased ability to accommodate with age (presbyopia). We characterised accommodation of observers aged 20 to 68 years using the slope of the linear portion of their stimulus-response functions. We also measured phoria, AC/A and CA/C ratios, visual acuity, and motor fusion limits. We determined a ‘zone of good stereo’ for each observer around screens at 1.3, 0.7, and 0.1 dioptres. We first measured their stereoacuity at each distance, using a random-dot-defined sinusoidal corrugation in depth (2-AFC task). These data were used to specify a no-conflict stimulus (coincident with the screen surface) for each observer for which performance was 90% correct. Adaptive staircases then controlled the stimulus position in-front-of and behind the screen to determine the point at which stereo performance was reduced by a criterion amount, yielding boundaries of the ‘zone of good stereo’. Tolerance of stereo depth perception to vergence-accommodation conflict was related to accommodation ability. The ‘zone of good stereo’ was largest for presbyopes. In younger observers phoria was predictive of the symmetry of the zone, as reported for discomfort in stereo displays (Shibata et al., 2011). These results are counter to the belief in the stereo industry that older viewers are more affected by stereo viewing than younger viewers. They are consistent instead with the idea that presbyopes are better matched to viewing stereoscopic imagery because their normal behaviour is to vary vergence with fixed accommodation. The results are relevant for optimising stereo hardware and content for different audiences.