Three layers of working memory: Focus-switch costs and retrieval dynamics as revealed by the N-count task.

Two experiments explored the process of switching items in and out of the focus of attention using a new paradigm, the N count task (adapted from Garavan, 1998; N varied from 1 to 4). This task yielded a focus size of one, indicated by a substantial focus switch cost for 2 count. Additionally, the focus switch costs in response time increased with working memory load, indicating an effortful search process occurring at a speed of about 240 ms/item. Maintaining and switching to and from a passive load did not increase the focus switch costs or decrease memory accuracy, indicating that there is no crosstalk between passive and active items. The results support a concentric theory of working memory: a small focus at its core, a surrounding area of (at least) three readily available items referred to as the outer store, and a still wider region of passive storage, possibly more long term memory than working memory.