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Andrew T. Smith, Matthew B. Wall; Human brain regions that are responsive to optic flow only when the flow is consistent with egomotion. Journal of Vision 2008;8(6):65. doi: https://doi.org/10.1167/8.6.65.
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© ARVO (1962-2015); The Authors (2016-present)
Primate visual cortical area MST is responsive to optic flow and can encode direction of heading but it may not directly signal motion of the body through space (egomotion). We identify two areas of the human brain that represent visual cues to egomotion more directly than does MST. Sensitivity to whether a flow pattern could have been caused by egomotion was tested with fMRI. Responses to a standard random-dot flow pattern were compared with responses to a 3×3 array of nine identical flow patches. Optic flow generated by egomotion can only have one centre of motion (expansion for forward motion). Consequently, the nine flow patches may drive neurons tuned to flow components such as expansion, but the overall stimulus is inconsistent with egomotion. Visual areas were defined in separate retinotopic mapping experiments. Areas V1–V4 and MT all responded about equally to both types of flow stimulus. MST also responded well to multiple patches but showed a modest preference for a single, egomotion-compatible patch. Putative area VIP in the anterior portion of the intraparietal sulcus showed much stronger selectivity, the response to a single flow stimulus being about twice that to the array. More striking still was the result in a new visual area, which we refer to as CSv (cingulate sulcus visual area). Here, a strong response was obtained with a single flow patch but the region was almost completely unresponsive to multiple patches. This requirement for egomotion-compatible stimulation may explain why CSv has not commonly been identified as a visual area. Various control experiments for dot motion parameters, size of motion patch and presence of motion boundaries all yielded similar results. We suggest that MST is merely an intermediate processing stage for visual cues to egomotion and that such cues are more comprehensively encoded by VIP and CSv.
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