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Thaddeus B. Czuba, Alexander C. Huk, Lawrence K. Cormack; Isolation of binocular 3D motion cues in human visual cortex. Journal of Vision 2011;11(11):710. doi: 10.1167/11.11.710.
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© ARVO (1962-2015); The Authors (2016-present)
The binocular perception of 3_dimensional (3D) motion relies on both disparity_based and velocity_based cues, but relatively little is known about their physiological substrate. Surprisingly, psychophysical evidence has shown that direction discrimination for 3D motion is primarily supported by the velocity_based cue (Czuba et al., 2010). Previous work has implicated extrastriate areas in and around human MT+ (Rokers et al. 2009, Likova & Tyler 2007; respectively) as being involved in 3D motion processing. But it is unclear whether, where, and how the velocity_based and disparity_based cues are combined in the brain.
Here, we use a combination of psychophysical and event_related fMRI adaptation protocols to explore the neural processing of the two binocular cues to 3D motion. Identical random dot stimuli were viewed in a mirror stereoscope in both the psychophysics and fMRI. Observers adapted to 100 s of 3D motion directly towards or away from them. This 3D motion adaptation was followed by a series of 1 s probes, which moved in either the ‘same’ or ‘opposite’ direction as the adapter, and a subsequent 4 s top-up adaptation. In the imaging studies, attention was controlled using a demanding color-change detection task, and probe stimuli were occasionally omitted to isolate the probe response per se (Larsson et al., 2006).
We observed large psychophysical 3D adaptation effects that could not be accounted for by any reasonable inheritance of 2D effects. In good agreement, the fMRI clearly showed adaptation in (independently-defined) human MT+, but not in V1, implying a central role for MT+ in 3D motion processing. These results lay the groundwork for testing whether both the velocity-based and disparity-based cues are processed by a common mechanism selective for 3D motion direction.
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