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Abstract:
The ventral (occipitotemporal) pathway has been implicated in
object perception and the dorsal (occipitoparietal) pathway in the
visual guidance of actions. Recent human fMRI studies have shown
that the lateral occipital complex (LOC) is involved in the visual
processing of object shape. Are regions in the human parietal
cortex activated more strongly by action tasks than perceptual
judgements performed on the same objects? We tested this question
in an fMRI study, in which the observers had to judge whether two
dots placed on the contour of 3D objects supported a stable grip on
the objects (grasping task) or whether they defined a boundary
between object parts (perceptual judgement). Regions in the
anterior intraparietal cortex (AIP) were activated significantly
more strongly when the observers performed the grasping task than
the perceptual judgement. A second experiment showed that the AIP
region showing stronger responses for the grasping than the
perceptual task, when localized independently in each subject,
produced a significantly higher response for intact images of
objects than for scrambled images of the same objects. These
results suggest that regions in the human parietal cortex primarily
involved in action tasks may represent information about shape.
Preliminary studies suggest differences between the LOC and the AIP
in the representation of shapes across image changes (e.g. size and
orientation changes).
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