Spontaneous serial refreshing in verbal and spatial working memory?

Working memory is the cognitive system that keeps a limited amount of information temporarily accessible for ongoing cognition. One proposed mechanism to keep information active in working memory is refreshing. Refreshing is assumed operate serially, reactivating memory items one by one by bringing them into the focus of attention during retention. We report two experiments in which we examine evidence for the spontaneous occurrence of serial refreshing in verbal working memory (Experiment 1, using letters as memoranda) and in visuo-spatial working memory (Experiment 2, using locations as memoranda). Participants had to remember series of red memory items, and black probes were presented between these memory items, with each probe to be judged present in or absent from the list presented so far, as quickly as possible (i.e., the probe-span task). Response times to the probes were used to examine whether the content of the focus of attention changed over time, as would be expected if serial refreshing occurs spontaneously during inter-item pauses. Contrary to this hypothesis, our results indicate that the last-presented memory item remained in the focus of attention during the inter-item pauses of the probe-span tasks. These findings confirm the boundary conditions of spontaneous serial refreshing that were previously observed for verbal working memory and extend them to visuo-spatial working memory. Implications for working memory maintenance are discussed.