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Mark Williams, Chris Baker, Hans Op de Beeck, Sabin Dang, Christina Triantafyllou, Nancy Kanwisher; Location-invariant object information in foveal retinotopic cortex. Journal of Vision 2008;8(6):38. doi: 10.1167/8.6.38.
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© ARVO (1962-2015); The Authors (2016-present)
According to standard theories of object perception, information in early stages of the visual hierarchy is tied to stimulus location, with more abstract ‘position-invariant’ representations of object shape achieved only at later stages. Here we present a new phenomenon that challenges this standard view: the pattern of fMRI response in foveal retinotopic cortex contains position-invariant information about objects presented outside the fovea. Subjects fixated centrally while viewing three categories of novel objects. In each trial, two objects were presented simultaneously in diagonally opposite peripheral retinal locations. These two objects were always from the same object category, and subjects were asked whether the two objects were identical or subtly different exemplars of that category. We then used multivariate pattern analysis methods to ask whether information about object category was present in the pattern of response across voxels in each of several cortical regions of interest (ROIs). Same-category correlations were higher than different-category correlations in the LOC, a region with a well-established role in shape representation. Astonishingly, however, correlations in the foveal region of retinotopic cortex were also higher for same-category than different-category pairs. This object information in foveal retinotopic cortex is behaviorally relevant: i) it is present during a discrimination task on objects presented in the periphery, but not a color discrimination task performed on the same stimuli, and ii) stronger information in foveal cortex is correlated across subjects with higher task performance. These findings suggest that position-invariant object information is fed back from higher areas to foveal retinotopic cortex, improving performance. Control experiments ruled out differential eye movements across object categories, activation from the fixation cross itself, or spillover activation from peripheral retinotopic cortex or from LOC. Instead, our data strongly suggest that position-invariant object information from higher cortical areas is fed back to foveal retinotopic cortex, improving task performance.
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