Object switching within working memory is reflected in the human event-related brain potential

In two experiments applying a memory updating task subjects are asked to perform several arithmetic operations on stored numbers. From a trial-to-trial perspective these operations could be either performed on a previously processed item or on a new item which requires an object switch in working memory. Object switching results in prolonged operation times; these operation time costs reflect the switch of the focus of attention to the relevant information. Event-related brain potentials obtained in object switch trials show an increased P3a around 300 ms and a late, central negative component between 400 ms and 500 ms. The data suggest that the P3a may reflect the unhitching of the focus of attention from the current information or task set through the inhibition of the prepared response while the late negative component may reflect the allocation of the focus of attention to another object in working memory. The present results are best explained within a controlled attention view of working memory supporting the idea that object switching relies on the ability to orient the focus of attention within working memory.