Primate visual cortex is segregated into at least two functionally discrete pathways - one that processes motion information and one that processes shape information. However, object motion is a powerful cue for the perceptionof three-dimensional (3D) shape, implying that the two types of information - motion and form - are well integrated.We conducted a series of fMRI experiments aimed at identifying the brain regions involved in inferring 3D shape-from-motion cues. For each subject, we identified regions in occipital-temporal cortex that were activated when perceiving: (1) motion in unstructured random-dot patterns, (2) 2D and 3D line drawing shapes, and (3) 3D shapes defined by motion cues (shape-from-motion, SFM). We found non-overlapping, adjacent areas activated by random motion and line drawing shapes. In addition, we found that SFM stimuli significantly increased activity in only one of the areas identified with either the random motion or line-drawing stimuli, the superior lateral occipital (SLO)region, indicating this area may be important for integrating motion and form information. Closer analyses suggest that SFM and line drawings are processed in separate but closely located sub-regions in SLO. Expanding the analysis to the entire cortex identified a parietal area that had overlapping activity to SFM and line drawings and increased activity to 3D versus 2D shapes. We suggest this area is important for integrating shape information from cue-dependent lateral occipital regions. We also observed significant activity reductions in primary visual cortex (V1) when visual elements (motion vectors and line segments) were grouped into objects, suggesting that activity in early visual areas is reduced as a result of grouping processes performed in higher areas.
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