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Katherine Bettencourt, Yaoda Xu; Decoding reveals distractor modulation of visual short-term memory contents in occipital but not in parietal cortices. Journal of Vision 2014;14(10):899. doi: 10.1167/14.10.899.
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Recently, there has been considerable debate on where the contents of visual short-term memory (VSTM) are stored. Univariate fMRI analyses have suggested that regions in the parietal lobe, in particular superior intraparietal sulcus (IPS), play a central role in VSTM storage. In contrast, fMRI multivariate pattern analysis (MVPA), has implicated primarily sensory cortices, in particular early visual cortex, in the storage of visual information. These findings prompt two important questions: 1) what does the dissociation between these techniques tell us about how VSTM is stored in the brain, and 2) if early visual areas, whose main role is to process incoming visual stimuli, are involved in the storage of VSTM, what happens to that stored information when subsequent visual information must be processed? We examined these questions across three fMRI studies using MVPA. We found, supporting previous univariate findings, that the memory of a particular orientation could be successfully decoded in superior IPS, regardless of the presence of distracting visual information during the delay. In early visual cortex, however, decoding performance depended, not only on whether distractors were present, but also on participants foreknowledge of their presence. When participants knew distractors would be present, decoding performance for the remembered grating fell to chance. Decoding accuracy rose as the probability of distraction decreased, suggesting a switch in participants strategy based on their knowledge of whether distractors would be present. Behavioral performance was not affected by the presence of distractors. These results bring together the univariate and MVPA literature and demonstrate that parietal cortex plays a central role in VSTM information storage. Early visual areas, however, are unlikely to be essential for memory storage, and may reflect cognitive processes, such as visual rehearsal or imagery, that are brought online, particularly under low visual processing loads, to support the maintenance of memory representations.
Meeting abstract presented at VSS 2014
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