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Abstract

Recent human fMRI studies have implicated separate cortical areas in the analysis of visual motion (i.e. MT/MST) and the processing of object shape (i.e. lateral occipital complex-LOC). However, the perception of object motion requires the visual system to integrate information about the shape and the motion of objects. Is MT/MST involved in the analysis of both object shape and visual motion? We tested this question by collecting functional MRI images with echo-planar head coil imaging at 1.5T while subjects viewed visual stimuli of various kinds. First we localized MT/MST and the LOC individually in each subject and then we tested for fMRI responses in these regions when the observers were presented with intact images of objects and scrambled versions of the same objects that have no clear shape structure. Higher responses to intact than scrambled images of objects were observed in both MT/MST and the LOC. These object selective responses in MT/MST were observed for moving objects and static 3D objects defined by binocular (i.e. disparity) or monocular (i.e. shading) depth cues but not for 2D silhouettes of objects. In contrast, the LOC showed shape selective responses to all of these types of objects. These results implicate MT/MST in shape processing and perhaps in integrating information about the shape and motion of objects. Moreover, the strong response to 2D shapes in the LOC but not in MT/MST suggest that the LOC may be involved in the recognition of both 2D and 3D objects, whereas MT/MST may be involved in the visual guidance of object-directed actions.