Neural Modulation by Binocular Disparity Greatest in Human Dorsal Visual Stream
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Abstract
Although cortical
activation to binocular disparity can be demonstrated throughout
occipital and parietal cortices, the relative contributions to depth
perception made by different human cortical areas have not been
established. To investigate whether different regions are optimized for
specific disparity ranges, we have measured the responses of occipital
and parietal areas to different magnitudes of binocular disparity.
Using stimuli consisting of sinusoidal depth modulations, we measured
cortical activation when the stimuli were located at pedestal
disparities of 0, 0.1, 0.35, and 0.7° from fixation. Across all areas,
occipital and parietal, there was an increase in BOLD signal with
increasing pedestal disparity, compared with a plane at zero disparity.
However, the greatest modulation of response by the different pedestals
was found in the dorsal visual areas and the parietal areas. These
differences contrast with the response to the zero disparity plane,
compared with fixation, which is greatest in the early visual areas,
smaller in the ventral and dorsal visual areas, and absent in parietal
areas. Using the simultaneously acquired psychophysical data we also
measured a greater response to correct than to incorrect trials, an
effect that increased with rising pedestal disparity and was greatest in
dorsal visual and parietal areas. These results illustrate that the dorsal
stream, along both its occipital and parietal branches, can reliably
discriminate a large range of disparities