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Won Mok Shim, Nancy Kanwisher; Visual working memory information in foveal retinotopic cortex during the delay. Journal of Vision 2010;10(7):779. doi: 10.1167/10.7.779.
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Several studies have implicated early retinotopic cortex in the storage of low-level visual information in working memory over a delay. An intuitive interpretation of these findings is that visual working memory for visual features reflects a continuation of activity (whether synaptic or spiking activity) in the neural populations that originally responded to the stimulus perceptually. Here we propose and test a more radical hypothesis, based on our recent discovery of a novel form of feedback in the visual system (Williams et al., 2008): that visual working memory information is represented in foveal retinotopic cortex, no matter where in the visual field the stimulus was first presented. In order to test this hypothesis, we used fMRI and pattern classification methods to examine whether the foveal area contains information about objects presented in the periphery during a working memory delay. During each trial, a single memory sample (drawn from one of two categories of novel 3D objects) was briefly presented in a peripheral location, followed by a 14s delay period. A probe appeared subsequently, followed by another 14s interval, and subjects reported whether it was identical to or different from the memory sample. The results show that the pattern of fMRI responses in the foveal cortex, where no stimulus was presented, contains position-invariant information about the category of objects presented in a peripheral location during the delay period, but not during the inter-trial interval when no stimulus is held in memory. Furthermore, over the course of the delay period, object information decreases at the location in retinotopic cortex corresponding to the stimulus location, whereas it increases at the foveal region, suggesting a transfer of visual information from the stimulus location to foveal cortex. These findings indicate that working memory information arises in foveal retinotopic cortex regardless of where the stimulus is presented.
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