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Deborah Giaschi, Amy Zwicker, Simon Au Young, Bosco Lee, Bruce Bjornson; The role of area V5/MT+ in the centripetal bias in global motion perception. Journal of Vision 2007;7(9):751. doi: 10.1167/7.9.751.
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© ARVO (1962-2015); The Authors (2016-present)
We previously reported lower coherence thresholds for centripetal (inward) relative to centrifugal (outward) frontoparallel global dot motion (VSS 2004, 2005). This direction anisotropy was observed at fast but not slow speeds of motion. The purpose of the present study was to examine the role of the motion sensitive cortical area V5/MT+ in this speed-tuned centripetal bias using functional MRI. A block-design localizer task in which epochs of dots in expanding/contracting radial motion alternated with epochs of stationary dots was used to identify area V5/MT+ in six adults with normal vision. On the global motion centripetal (centrifugal) task, epochs of dots moving from the left and right, or from the top and bottom, toward (away from) the center alternated with epochs of stationary dots. The coherence of the moving dots was 85%, 25% or 0% on alternate blocks. The motion speed of each run was either 8 or 1 deg/s. A region of interest analysis revealed greater activation in V5/MT+ at 25% coherence than at 85% or 0% coherence. This region also responded more to centripetal motion than to centrifugal motion at both speeds. These results suggest that V5/MT+ plays a role in the direction, but not the speed-tuning, of the perceptual motion anisotropies. A centripetal bias is unlikely to be the result of selective exposure to optic flow, which is usually in a centrifugal direction. A centripetal bias has instead been linked to the precise control of arm movements towards fixation (Edwards & Badcock, 1993; Shirai, Kanazawa & Yamaguchi, 2006; Steinmetz, Motter, Duffy & Mountcastle, 1987). We speculate that the centripetal bias for optic flow in the central visual field, reported here, is related to mechanisms for visually-guided reaching, while the centrifugal bias for optic flow in the peripheral visual field, reported by others, is related to mechanisms for locomotion.
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