Visual Search Demands Dictate Reliance on Working Memory Storage

Previous research suggested that working memory (WM) does not play any significant role in visual search. In three experiments, we investigated the search difficulty and individual differences in WM capacity as determinants of WM involvement during visual search tasks, using both behavioral and electrophysiological markers [i.e., the contralateral delay activity (CDA), which is a marker for WM capacity allocation]. Human participants performed a visual search task that contained a target, neutral distractors, and a flanker distractor. Overall, we found that, as the search difficulty increased (as indicated by longer reaction times), so did the role of WM in performing the search task (as indicated by larger CDA amplitudes). Moreover, the results pinpoint a dissociation between the two types of factors that determined the WM involvement in the search process. Namely, individual differences in WM capacity and search difficulty independently affected the degree to which the search process relied on WM. Instead of showing a progressive role, individual differences in WM capacity correlated with the search efficiency in all search conditions (i.e., easy, medium, and difficult). Counterintuitively, individuals with high WM capacity generally relied less on WM during the search task.