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Reza Rajimehr, Wim Vanduffel, Roger Tootell; Retinotopy versus category specificity throughout primate cerebral cortex. Journal of Vision 2007;7(9):107. doi: 10.1167/7.9.107.
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In initial stages of the visual hierarchy, stimuli are represented in point-to-point (retinotopic) maps. However at higher stages in the ventral stream, it has been proposed that the retinotopic map is converted into a category-selective cortical architecture (e.g. face representations in IT cortex of humans and macaques). To independently map and compare these two dimensions, we acquired fMRI from two awake monkeys and six human subjects, while presenting stimuli consisting of face- or place-based images, confined to retinotopically-specific apertures, during continuous central fixation. This common data was analyzed in two different ways: 1) based on category (faces vs. places), and 2) based on retinotopic location (e.g. foveal vs. peripheral stimuli). In macaques, the category comparison revealed face-selective regions in the posterior IT/STS, anterior IT, lateral parietal and inferior frontal cortex, consistent with previous studies. In human subjects, analogous face-selective regions were revealed in two major areas described previously: the fusiform gyrus (including FFA), and lateral occipital cortex (∼V4d) - plus a smaller region in anterior temporal lobe, perhaps homologous to the anterior temporal face patch in macaques. The retinotopy analysis demonstrated a surprising degree of retinotopic organization in IT cortex. In both human and macaque subjects, each face-selective region typically contained subdivisions selective for either foveal or peripheral stimuli, or both. Retinotopic maps (polar and eccentricity) were also revealed in more than 20 additional areas in macaques, including frontal and parietal cortex, association cortex, and ventral occipital regions not described previously. The overall findings suggest a conjoined representation of object and space selectivity in the ventral pathway - not a ‘pure’ representation of object category.
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