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Paige Scalf, Laura Cacciamani, Morgan Barense, Mary Peterson; Representation of object parts and wholes in V2 modified by medial temporal lobe structures. Journal of Vision 2013;13(9):1002. doi: https://doi.org/10.1167/13.9.1002.
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Recent research has demonstrated (a) that the perirhinal cortex (PRC) encodes complex object-level configurations of features, and (b) these representations participate in discriminating familiar versus novel configurations. The ventral visual stream is able to identify familiar object parts as such even in the face of PRC damage, although it cannot identify their configuration as correct or incorrect Barense et al. (2011). Here, we use fMRI to investigate whether extrastriate cortex in the intact brain a). is sensitive to the configuration of parts of familiar objects and b). covaries with activation in the PRC. Participants viewed peripherally presented silhouettes (nearest edge 4°) that portrayed familiar or novel objects. There were 3 types of silhouettes: familiar configurations (objects that exist in the real world); part-rearranged novel configurations (rearranged parts of the familiar configurations); and novel configurations created by (inverted part-rearranged novel configurations) (See figure 1). To our surprise, we found visual field asymmetries in the manner in which object parts were encoded in both V2 and the region of the medial temporal lobe (MTL) with which V2 activation covaried (see figures 2 and 3). When presented to the right visual field (RVF), familiar parts in their familiar rather than scrambled configuration evoked stronger activation in V2 and PRC (area 35). When presented to left visual field (LVF), however, this pattern of activation was reversed and covaried with activation BA 38. These data confirm that the V2 is sensitive to the configural status of familiar parts, but because the receptive fields of V2 neurons are large enough to encode object parts (2°) but not entire objects (6°), this sensitivity is likely modulated by feedback from structures within the MTL. We conclude that active perception of object configuration relies on both early visual cortex and structures within the MTL.
Meeting abstract presented at VSS 2013
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