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Matthew L. Patten, Andrew E. Welchman; fMRI responses in higher dorsal areas relate to depth discrimination for both coarse and fine disparity tasks. Journal of Vision 2011;11(11):335. doi: https://doi.org/10.1167/11.11.335.
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The cortical processing of coarse and fine binocular disparities is suggested to be specialised in the dorsal and ventral pathways respectively. Here we use human fMRI to test for patterns of brain activity that relate to performance on coarse and fine disparity tasks along the dorsal and ventral visual pathways. We used parametric stimulus variations to manipulate participants' performance in coarse and fine depth tasks and sought to identify cortical regions that contained information that varied in line with perceptual judgments. Participants viewed random-dot stereograms that contained a target plane with crossed (near) or uncrossed (far) horizontal disparity and judged its position (near or far) relative to the background. For the coarse task, we varied the proportion of dots located at the depth of the target plane (±6 arcmin). In the fine task, we varied the relative disparity between the target plane and its surround. We measured event-related fMRI responses and used multi-voxel pattern classification methods to determine cortical regions that contained information about the disparity-defined depth. Correlating the performance of human observers with that of the classifier showed a close relationship between behavioural performance and fMRI brain patterns in dorsal regions for the coarse task (V3A, V7, VIPS, POIPS). Interestingly, this result was also evident in higher dorsal regions for the fine task. However, we did not observe significant variations in classification performance in line with perceived depth for either task in regions of the ventral pathway. Our results suggest the important contribution of higher dorsal visual areas when making both coarse and fine depth judgments.
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