Temporal dynamics of multiple attentional template activation during preparation for search

Visual search for known objects is guided by attentional templates (target representations held in working memory), which are activated prior to search. We used an RSVP paradigm to track the temporal dynamics of template activation when multiple colours are task relevant. Search displays containing a pre-defined colour target and five differently coloured distractors were shown every 1600ms. Every 200ms between successive searches, a target- or distractor-colour probe was presented. N2pc components (electrophysiological markers indexing attentional capture) were measured at each probe’s temporal position prior to search to determine when in time attentional templates were activated. Target-colour probe N2pc amplitudes increased during the preparation period and were largest for probes directly preceding the next search display. This pattern of transient template activation was identical in single- and two-colour search and probe N2pcs were comparable in size when participants searched for one versus two colours, when the two possible target colours were equiprobable or differed in their likelihoods, and when they changed randomly versus predictably. Transient template activation was also observed in three-colour search, but only when target colours appeared randomly. When they alternated predictably between search episodes, only probes that matched the upcoming target colour triggered N2pcs. This suggests that two attentional templates can be activated in parallel without any apparent costs. However, with three templates, participants prefer to make use of strategic opportunities to reduce working memory load. Notably, distractor-colour probes never triggered N2pcs, demonstrating perfect colour-selectivity in one- two-, and three-colour search.