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Abstract:
Interactions in our dynamic environment require that the visual system processes both the form and motion of objects. Different cortical areas are thought to be involved in the processing of visual motion (hMT+/V5), kinetic boundaries (KO) and object shape (LOC). The goal of this study was to investigate whether these areas are involved in the integration of form and motion information and the perception of shapes defined by motion coherence. To this end, we used human event-related fMRI and employed stimuli in which the shape was defined by the relative motion of random dots in the shape and the background. We manipulated the perception of these shapes by independently varying the motion coherence of the dots in the shape and the background. Increased motion coherence in either the shape or the background improved the behavioral performance of the observers in a shape categorization task. fMRI responses in area KO were stronger when the motion coherence in the background was increased. In contrast, fMRI responses in the LOC were consistent with the behavioral performance of the observers; that is, enhanced fMRI responses were observed with increased motion coherence in either the shape or the background. Interestingly, hMT+/V5 showed activation patterns similar to the LOC, suggesting strong interactions between ventral (LOC) and dorsal (hMT+/V5) visual areas in shape perception from motion coherence. To further investigate shape representations from motion in the different visual areas we tested for fMRI adaptation across changes in shape and motion direction. Recovery from adaptation was observed across changes in shape in the LOC, KO, and hMT+/V5, but not in early visual areas. These findings suggest that not only object (LOC) but also motion-related areas (KO, hMT+/V5) are involved in the selective representation and perception of shapes defined by motion coherence.
