A direct neural measure of variable precision representations in visual working memory

Visual working memory (VWM) is an active representation enabling the manipulation of item information even in the absence of visual input. A common way to investigate VWM is to analyze the performance at later recall. This approach, however, leaves uncertainties about whether the variation of recall performance is attributable to item encoding and maintenance or to the testing of memorized information. Here, we record the contralateral delay activity (CDA), an established electrophysiological measure of item storage and maintenance, in human subjects performing a delayed orientation precision estimation task. This allows us to link the fluctuation of recall precision directly to the process of item encoding and maintenance. We show that for two sequentially encoded orientation items, the CDA amplitude reflects the precision of orientation recall of both items, with higher precision being associated with a larger amplitude. Furthermore, we show that the CDA amplitudes for the items vary independently from each other, suggesting that the precision of memory representations fluctuates independently. NEW & NOTEWORTHY The present work demonstrates for the first time that the contralateral delay activity (CDA), an online electrophysiological measure of the number of representations maintained in memory, is also a reliable measure of the precision of memory representations. Furthermore, we show that the CDA fluctuates independently for individual items held in memory, thereby providing unambiguous direct neurophysiological support for independently fluctuating memory representations.