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Nature. 2009 Apr 2;458(7238):632-5. doi: 10.1038/nature07832. Epub 2009 Feb 18.

Decoding reveals the contents of visual working memory in early visual areas.

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1
Psychology Department and Vanderbilt Vision Research Center, Vanderbilt University, Nashville, Tennessee 37240, USA.

Abstract

Visual working memory provides an essential link between perception and higher cognitive functions, allowing for the active maintenance of information about stimuli no longer in view. Research suggests that sustained activity in higher-order prefrontal, parietal, inferotemporal and lateral occipital areas supports visual maintenance, and may account for the limited capacity of working memory to hold up to 3-4 items. Because higher-order areas lack the visual selectivity of early sensory areas, it has remained unclear how observers can remember specific visual features, such as the precise orientation of a grating, with minimal decay in performance over delays of many seconds. One proposal is that sensory areas serve to maintain fine-tuned feature information, but early visual areas show little to no sustained activity over prolonged delays. Here we show that orientations held in working memory can be decoded from activity patterns in the human visual cortex, even when overall levels of activity are low. Using functional magnetic resonance imaging and pattern classification methods, we found that activity patterns in visual areas V1-V4 could predict which of two oriented gratings was held in memory with mean accuracy levels upwards of 80%, even in participants whose activity fell to baseline levels after a prolonged delay. These orientation-selective activity patterns were sustained throughout the delay period, evident in individual visual areas, and similar to the responses evoked by unattended, task-irrelevant gratings. Our results demonstrate that early visual areas can retain specific information about visual features held in working memory, over periods of many seconds when no physical stimulus is present.

PMID:
19225460
PMCID:
PMC2709809
DOI:
10.1038/nature07832
[Indexed for MEDLINE]
Free PMC Article
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