When Working Memory May Be Just Working, not Memory

Abstract

The N-back task is often considered to be a canonical example of a task that relies on working memory (WM), requiring both active maintenance of representations of previously-presented stimuli and also processing of these representations. In particular, the set-size effect in this task (e.g., poorer performance on 3-back than 2-back judgments), as in others, is commonly interpreted as indicating that the task relies on active maintenance in a limited-capacity WM system. Here, we consider the alternative possibility that retention in episodic memory (EM) rather than working memory can account for both set-size and lure effects in the N-back task. Accordingly, performance in the N-back task may reflect engagement of the processing ("working") function of WM but not necessarily the retention ("memory") function of WM. To demonstrate this point using a neural network architecture, we constructed a model that was augmented with an EM component, but lacked any capacity to actively maintain information in WM, and trained it to perform the N-back task. We show that this model can account for the set-size and lure effects obtained in an N-back study by Kane et al. (2007), and that it does so as a result of the well-understood effects of temporal distinctiveness on EM retrieval. These findings add to a growing body of evidence that performance on tasks commonly assumed to rely on WM may, in addition or alternatively, rely on EM.