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Christian Quaia, Boris Sheliga, Lance Optican, Bruce Cumming; Processing of first and second order binocular disparity by the human visual system. Journal of Vision 2012;12(9):39. doi: 10.1167/12.9.39.
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In order to study how binocular disparity is detected by the visual system, we recorded short-latency disparity vergence responses (DVRs) from three human subjects. Stimuli occupied the whole screen (48deg H x 36deg V) and were either single sinusoidal gratings or plaids. The single gratings (0.25 cpd, 32% contrast) were oriented vertically (or horizontally) and were presented dichoptically to the two eyes with a crossed/uncrossed (or left-hyper/right-hyper) disparity of 1 deg. As expected from previous studies, these stimuli induced strong short-latency (70 ms) horizontal (or vertical) DVRs in all subjects. The plaids were composed of two gratings having the same spatial frequency and contrast (0.25 cpd, 32% contrast): a vertical (or horizontal) grating with a crossed/uncrossed (or left-hyper/right-hyper) disparity of 1 deg, and an oblique (45 deg) grating with zero disparity. The gratings composing the plaid had thus either horizontal or vertical disparity (first order disparity), whereas the two dimensional pattern had an oblique (i.e., both horizontal and vertical) disparity (second order disparity). When tested with these stimuli, all subjects generated a strong short-latency (70 ms) DVR in the direction predicted by the first order disparity. This DVR was followed ~20 ms later by an additional response in the direction predicted by the second order disparity. The same phenomena were replicated with low contrast (5%) gratings. These results demonstrate that the extraction of second order disparity occurs, but it takes considerably more time than the extraction of first order disparity.
Meeting abstract presented at VSS 2012
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