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Peter Kohler, Wesley Meredith, Anthony Norcia; Characterizing late-developing binocular motion mechanisms in human visual cortex. Journal of Vision 2018;18(10):1063. doi: 10.1167/18.10.1063.
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The visual system can detect motion-in-depth by tracking changes in disparity over time (CDOT), or by computing inter-ocular velocity differences (IOVD). Here we measure responses to these two distinct cues in human visual cortex. We present data from adult (5 experiments, total n=63) and infant participants (n=34) generated using a steady-state VEP design (Kohler et al., VSS, 2016) where random dots moving periodically at 2 Hz generate disparity or 2-D motion, which can be horizontal or vertical and depending on the reference, relative or absolute. The first harmonic of the dot motion frequency will capture responses that differ with motion direction, while the second harmonic will capture responses that do not. The first harmonic was robust only for displays containing horizontal relative disparity cues that produced a strong percept of motion-in-depth. It was weak for conditions with vertical relative disparity, and absent for disparity conditions with no reference, with dots that were uncorrelated or anti-correlated between the two eyes, and without plane-breaking. These findings, and the fact that first harmonic was weak in infants, are consistent with a late-developing image segmentation response that relies on CDOT. The second harmonic was stronger for relative motion than relative disparity, for both vertical and horizontal displays. This effect persisted with uncorrelated and anti-correlated dots. When absolute responses were measurable, absolute disparity produced stronger responses than absolute motion. For infants, disparity also produced stronger responses than motion, and relative and absolute responses were comparable. These findings are consistent with the second harmonic indexing motion-related responses that rely on IOVD, and demonstrate that the weaker responses to disparity compared to 2-D motion are driven by a late-developing mechanism that requires a reference, but not motion-in-depth. This mechanism, likely related to binocular opponent processes, may offer an alternative explanation to psychophysical stereo-movement suppression effects (Tyler, 1971).
Meeting abstract presented at VSS 2018
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