Individual differences in the allocation of attention to items in working memory: Evidence from pupillometry.

We utilized pupillary responses as an online measure of attentional allocation and fluctuations in attention in order to better examine both how attention is allocated to items in working memory (WM) and individual differences therein. We found that the pupillary response during a delay was modulated by the number of items to be held in memory, reaching asymptote close to capacity limits. Furthermore, we found that during the delay, how individuals allocated attention to items in WM depended on the number of items to be held, as well as on an individual's capacity. Finally, we found that pretrial pupil diameter distinguished correct and error responses and that individuals with more variability in pretrial pupil diameter had lower behavioral capacity estimates. These results suggest that individual differences in WM are due both to differences in the amount of attention that can be allocated to maintain items in WM and to differences in fluctuations in attention control across trials.