Dynamic shape integration in extrastriate cortex.
BACKGROUND
In anorthoscopic viewing conditions, observers can perceive a moving object through a narrow slit even when only portions of its contour are visible at any time. We used fMRI to examine the contribution of early and later visual cortical areas to dynamic shape integration. Observers' success at integrating the shape of the slit-viewed object was manipulated by varying the degree to which the stimulus was dynamically distorted. Line drawings of common objects were either moderately distorted, strongly distorted, or shown undistorted. Phenomenologically, increasing the stimulus distortion made both object shape and motion more difficult to perceive.


RESULTS
We found that bilateral cortical activity in portions of the ventral occipital cortex, corresponding to known object areas within the lateral occipital complex (LOC), was inversely correlated with the degree of stimulus distortion. We found that activity in left MT+, the human cortical area specialized for motion, showed a similar pattern as the ventral occipital region. The LOC also showed greater activity to a fully visible moving object than to the undistorted slit-viewed object. Area MT+, however, showed more equivalent activity to both the slit-viewed and fully visible moving objects.


CONCLUSIONS
In early retinotopic cortex, the distorted and undistorted stimuli elicited the same amount of activity. Higher visual areas, however, were correlated with the percept of the coherent object, and this correlation suggests that the shape integration is mediated by later visual cortical areas. Motion information from the dorsal stream may project to the LOC to produce the shape percept.
Yin
Carol
C
Computation and Neural Systems, Division of Biology, MC 139-74, California Institute of Technology, Pasadena, CA 91125, USA.
Shimojo
Shinsuke
S
Moore
Cassandra
C
Engel
Stephen A
SA
D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009778:Occipital Lobe / Q000033:anatomy & histology / Q000378:metabolism*; D010364:Pattern Recognition, Visual / Q000502:physiology*