Disparity Processing in Sensory and Motor Functions

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Traditional theories going back 154 years to Wheatstone propose that stereoscopic depth perception is stimulated early in the visual cortex by disparities between the retinal images on the left and right eyes (retinal disparity). Alternatively, stereopsis and binocular eye movements could be stimulated in sensory-motor regions of the brain by binocular disparities between perceived directions of the two ocular images (head-centric disparity). These perceived directions result from a combination of retinal image location and eye position information. Under normal viewing conditions, retinal disparities are indistinguishable from headcentric disparities, so it is not possible to determine which stereoscopic vision is based on. However, the two forms of disparity do have different magnitudes when a briefly flashed target is presented with a small interocular time delay near the onset of a rapid eye-movement (saccade). The saccade causes unequal distortions of perceived direction by the two eyes, and these differences produce stereo-depth. This is the first evidence that eye movements can influence binocular disparity stimuli for stereopsis and that binocular disparity is represented in headcentric coordinates.With support of the National Science Foundation, Dr. Schor will investigate how rapid (saccadic) eye movements produce distortions of stereoscopic-depth perception. These depth distortions reveal how the brain represents binocular disparities that stimulate stereopsis and binocular eye movements. In addition to improving our basic understanding of stereopsis, this work has implications concerning how eye movements might influence the accuracy of depth stimulated by computer-simulated stereo displays that present alternate frames to each of the two eyes. The resulting distortions of space could influence performance in depth localization and aiming tasks.