Switching attention from internal to external information processing: a review of the literature and empirical support of the resource sharing account

Despite its everyday ubiquity, not much is currently known about cognitive processes involved in flexible shifts of attention between external and internal information. An important model in the task-switching literature, which can serve as a blueprint for attentional flexibility, states that switch costs correspond to the time needed for a serial control mechanism to reallocate a limited resource from the previous task context to the current one. To formulate predictions from this model when applied to a switch between perceptual attention (external component) and working memory (WM; internal component), we first need to determine whether a single, serial control mechanism is in place and, subsequently, whether a limited resource is shared between them. Following a review of the literature, we predicted that a between-domain switch cost should be observed, and its size should be either similar or reduced compared to the standard, within-domain, switch cost. These latter two predictions derive from a shared resource account between external and internal attention, or partial independence among them, respectively. In a second phase, we put to the test these opposing predictions in four successive behavioral experiments by means of a new paradigm suited to compare directly between- (internal to external) and within-domain (external to external) switch costs. Across them, we demonstrated the existence of a reliable between-domain switch cost whose magnitude was similar to the within-domain one, thereby lending support to the resource sharing account.