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Intact implicit representation of object 3D structure in object agnosia

54.11, Tuesday, 19-May, 2:30 pm - 4:15 pm, Talk Room 1
Session: 3D Perception

Erez Freud1,2, Tzvi Ganel1,2, Galia Avidan1,2, Marlene Behrmann3,4; 1Department of Psychology, Ben-Gurion University of the Negev, 2Zlotowski Center fo Neuroscience, Ben-Gurion University of the Negev, 3Department of Psychology,Carnegie Mellon University, Pittsburgh, PA, 4Center for the Neural Basis of Cognition,Carnegie Mellon University, Pittsburgh, PA

The representation of object 3D structure in the human brain is fundamental for the recognition and visuomotor control of objects. Accordingly, multiple cortical regions along the dorsal and ventral visual streams have been shown to exhibit sensitivity to object structure. To examine the contribution of regions in the ventral stream to processing object 3D structure, we tested five patients with focal damage in the right ventral visual cortex. In a series of behavioral experiments, in which spatially possible and impossible objects were presented, the patients exhibited reduced explicit classifications of 3D structure compared to matched healthy and brain-damaged controls. Interestingly, however, evidence of implicit sensitivity to object 3D structure was revealed by superior performance for possible compared to impossible objects in tasks that did not require explicit classifications of object possibility. A corresponding pattern was also observed in an fMRI experiment in which participants passively viewed possible and impossible objects. Whereas in the matched controls, all object-selective regions showed sensitivity to object possibility, with greater response for impossible than possible objects, in the patients, only a subset of these regions showed such pattern of activity. An additional functional connectivity analysis showed an overall reduced connectivity between object-selective ROIs among the patients, with marked abnormality in the connections to the right inferior temporal sulcus. Taken together, the results suggest that, despite the central role of the right ventral stream in representing 3D structure, a degraded representation of object structure that suffices for some tasks (implicit) but not others (explicit) can still be derived even after damage to this region. This representation may be subserved by the distributed fashion in which 3D structure is represented in the human brain.

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