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Thomas Christophel, Polina Iamshchinina, Chang Yan, John-Dylan Haynes; Working memory contents outside the focus of attention are represented by different neural populations not in an activity-silent state. Journal of Vision 2017;17(10):1117. doi: 10.1167/17.10.1117.
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Some contents held in visual working memory are thought to be retained in a prioritized state typically referred to as the 'focus of attention', while other items are considered to be 'unattended', or 'accessory'. Attempts to identify and read out such unattended memory representations in the human brain using fMRI have so far only resulted in null findings, leading some to postulate that unattended items are retained in an 'activity-silent state', for example by synaptic mechanisms. Here, we revisited this important question to test an alternative explanation for previous null results: Attended and unattended items are retained by separate patterns of neural activity which might even be localized in different brain areas. In the experiment, participants memorized the orientation of two Gabor patches in an MRI scanner. A first cue, indicated that one of the two stimuli should be used for a first orientation change detection task making it the attended memory content for a first delay. After this first task, a second cue could select the other orientation for a second task, ensuring that participants had to maintain both orientations during the first delay. We analyzed fMRI data from this maintenance interval using cvMANOVA MVPA and a large set of regions of interest to independently identify information about the attended and the unattended item. Information about the attended orientation stored in working memory was found predominantly in V1, as well as inferior and superior parietal areas. Importantly, the information about the not prioritized or unattended working memory orientation was represented in the intraparietal sulcus within the same maintenance interval, where no information was found for the attended item. Finding separate representations of currently relevant and irrelevant working memories demonstrates separate activity-based storage mechanisms for attended and unattended items.
Meeting abstract presented at VSS 2017
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