Abstract
People need to often switch attention between external and internal sources of information, that is, external and internal attention, respectively. There has been a recent surge of research interest in this type of attentional flexibility, which has revealed that it is characterized by an asymmetrical cost, being larger for switching toward internal than external attention. This cost asymmetry has been explained in terms of an internal shielding benefit, that is, the maintenance of stable internal attention against external interference. Although it is currently unclear how internal information might be shielded from external input during switches, a likely candidate is perceptual decoupling. In this study, we instructed participants to repeat external or internal attention, or to switch between them from trial to trial, while simultaneously recording 64-channel EEG. At the behavioral level, we replicated the switch cost asymmetry. Our ERP analysis provided evidence for three different processing stages. First, participants prepared more strongly for an upcoming internal than external attentional selection, as reflected in the increased contingent negative variation component. Second, during internal trials, participants moreover showed a blunted sensory response, most notable in the P1 and N1 components, reflecting perceptual decoupling. Finally, we found an increased P2 component when switching toward internal attention compared with repeating it, indicating more stable perceptual decoupling on internal repetition trials, in line with an internal shielding benefit. We integrate these findings here with behavioral accounts of the cost asymmetry and conclude that perceptual decoupling provides a potential mechanism for the internal shielding benefit of attention.