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Maryam Vaziri Pashkam, Yaoda Xu; The contribution of human parietal cortex to conceptual categorization. Journal of Vision 2013;13(9):787. doi: 10.1167/13.9.787.
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© ARVO (1962-2015); The Authors (2016-present)
Categorizing objects based on their conceptual properties is one of the key functions of human cognition. Previous monkey physiological studies have indicated the direct involvement of the primate parietal cortex in visual object categorization. Using fMRI, here we address whether sub-regions of human posterior parietal cortex contribute to conceptual categorization of objects. On a given trial, we show observers an image depicting a bike, a sneaker, a hanger or a couch (20 different exemplars are used for each object class) and ask them to perform two orthogonal conceptual categorization tasks. In the indoor-outdoor task, observers would categorize hangers and couches as being indoor and bikes and sneakers as being outdoor; and in the small-large task, they would categorize hangers and sneakers as being small and couches and bikes as being large. Because the same 4 objects are categorized into two different groups across the two tasks, we are able dissociate conceptual categorization from basic visual categorization. Furthermore, by assigning the same motor responses to two of the objects across the two tasks, we are able to dissociate categorization from motor related neural responses. We extracted fMRI response patterns from five topographic areas along the human intra parietal sulcus as well as from superior IPS (sIPS) and inferior IPS (iIPS), two parietal regions previously shown to participate in visual object individuation and identification in a short-term memory task. Using multi voxel pattern analysis and a linear support vector machine, we show that of all the parietal regions examined, only sIPS is able to distinguish between the two instances of the same object across the two tasks. In other words, sIPS represents the same object differently depending on the conceptual categorization task required. These results reveal a possible role of human parietal cortex in conceptual categorization of objects.
Meeting abstract presented at VSS 2013
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