The capacity of visual short-term memory is highly limited, maintaining only three to four objects simultaneously1,2. This extreme limitation necessitates efficient mechanisms to select only the most relevant objects from the immediate environment to be represented in memory and to restrict irrelevant items from consuming capacity3,4,5. Here we report a neurophysiological measure of this memory selection mechanism in humans that gauges an individual's efficiency at excluding irrelevant items from being stored in memory. By examining the moment-by-moment contents of visual memory6, we observe that selection efficiency varies substantially across individuals and is strongly predicted by the particular memory capacity of each person. Specifically, high capacity individuals are much more efficient at representing only the relevant items than are low capacity individuals, who inefficiently encode and maintain information about the irrelevant items present in the display. These results provide evidence that under many circumstances low capacity individuals may actually store more information in memory than high capacity individuals. Indeed, this ancillary allocation of memory capacity to irrelevant objects may be a primary source of putative differences in overall storage capacity.
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This work was supported by grants from the US National Institute of Mental Health and the Oregon Medical Research Foundation.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Vogel, E., McCollough, A. & Machizawa, M. Neural measures reveal individual differences in controlling access to working memory. Nature 438, 500–503 (2005). https://doi.org/10.1038/nature04171