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Maryam Vaziri Pashkam, Yaoda Xu; Decoding visual object representation in human parietal cortex. Journal of Vision 2014;14(10):1307. doi: 10.1167/14.10.1307.
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© ARVO (1962-2015); The Authors (2016-present)
Although visual object representation has been discovered in the primate parietal cortex more than a decade ago, the nature of this representation remains largely unknown. Using fMRI and multiple voxel pattern analysis, here we investigated the represetnation of objects from eight different categories in human parietal cortex. The categories we used included face, body, house, cat, elephant, car, chair and scissors. The parietal regions we examined included five topographic areas along the intra-parietal sulcus (IPS) as well as superior and inferior IPS, two regions previously implicated in visual object individuation and identification, respectively. We also examined responses from retinotopically defined early visual areas, the object shape processing region in lateral occipital cortex and part of temporal cortex activated by our object stimuli. During the experiment, observers saw a sequential presentation of ten exemplar objects from each category and detected an occcasional 1-back repetition of the object. Using a linear support vector machine classifier, we obtained significant decoding of the different object categories in both occipito-temporal and parietal regions. Decoding in these regions was unaffected by whether intact object images or images equalized in luminance, contrast and spatial frequency were used. Decoding in occipito-temporal and most of the parietal regions were also unaffected by object position and size changes. In contrast, size and position changes removed successful decoding in early visual cortex, consistent with the nature of visual information representation in that region. These results demonstrate that objects from different categories can be represented distinctively in human parietal cortex. This representation shows both position and size invariance and is equally robust when lower-level visual feature differences among the categories are removed. Object representation in human parietal cortex thus likely reflects high levels of visual object processing, similar to what was found in occipital and temporal cortices.
Meeting abstract presented at VSS 2014
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