A working memory workout: how to expand the focus of serial attention from one to four items in 10 hours or less

Five individuals participated in an extensive practice study (10 1-hr sessions, 11,000 trials total) on a self-paced identity-judgment (1)n-back task (n ranging from 1 to 5). Within Session 1, response time increased abruptly by about 300 ms in passing from n = 1 to n > 1, suggesting that the focus of attention can accommodate only a single item (H. Caravan, 1998; B. McElree, 2001). Within Session 10, response time was dramatically reduced and increased linearly with n for n < or = 4, with a slope of about 30 ms. The data suggest that working memory consists of a focus of attention governed by a limited-capacity search, expandable through practice, and a content-addressable region outside the focus of attention.