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Bas Rokers, Larry Cormack, Alex Huk; 3D motion perception depends on eye-specific signals outside V1. Journal of Vision 2009;9(8):678. doi: 10.1167/9.8.678.
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© ARVO (1962-2015); The Authors (2016-present)
Perception of 3D motion relies on two dissociable binocular cues: changes in disparity, and interocular velocity differences (IOVDs). The IOVD cue requires that the visual system extracts monocular velocities from corresponding retinal regions. We performed psychophysical experiments in which a plaid (the sum of 2 sinusoidal component gratings) drifted in opposite directions in the two eyes. If IOVDs are extracted early in the motion processing stream, 3D motion percepts should be strongest when one of the components drifts horizontally. If IOVDs are extracted later, percepts should be strongest when the pattern motion is horizontal.
For all stimuli, we measured the strength of the 3D motion percept as a function of the overall stimulus orientation/direction. For ‘Type I’ plaids, the resulting tuning curve was narrowly centered on the pattern motion prediction, and very different than one obtained with a comparable stimulus in which the monocular half-images yielded percepts of transparent components rather than coherent pattern motion. For ‘Type II’ plaids, which yield very different component- and pattern- motion signals, perceived 3D motion was strongly affected by the plaid direction, confirming a distinct contribution of pattern motion signals.
Finally, we presented a novel ‘microcomponent‘ dichoptic stimulus that effectively bypassed binocular processing in early visual cortex. The stimulus consisted of small (0.5 deg diameter) randomly- oriented and -positioned drifting Gabors. All Gabor component velocities were compatible with a single global pattern motion. Gabors were spaced so that only one fell within any V1-sized receptive field. Moreover, they were dichoptically spaced such that no binocular overlap existed at the scale of V1 processing. This stimulus nonetheless produced compelling 3D motion percepts.
These results demonstrate that eye-specific circuitry exists outside V1, and must play a key role in 3D motion perception.
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