Abstract
In most visual working memory (WM) paradigms, subjects must remember a briefly-presented set of items across a blank retention period of one or more seconds. A common finding is that most subjects can accurately maintain about three items simultaneously. In this study, we examined whether these capacity limits are exclusively for maintaining items that are no longer present, or if similar limitations are observed for items that are continuously visible. To do this, we presented subjects with displays of simple objects and asked them to remember the colors of each item until the presentation of a test probe that appeared at the position of one of the items. The memory array was presented for either 100 ms, 500 ms, or 1000 ms, which resulted in blank retention intervals of 900 ms, 500 ms, or 0 ms. Surprisingly, we found both behavioral and electrophysiological evidence that the capacity limitations and neural mechanisms supporting performance (contralateral delay activity) were equivalent for displays in which the items were either not present during the retention interval or were continuously visible to the subject. These results suggest that capacity limits for simultaneously representing multiple items are not exclusive to WM maintenance of information that is no longer there, but also extend to perceptually present items.