The Capacity Limitations of Multiple-template Visual Search During Task Preparation and Target Selection

Visual search is guided by mental representations of target-defining features (attentional templates) that are activated in a preparatory fashion. It remains unknown how many templates can be maintained concurrently, and what kind of costs are associated with multiple-template versus single-template search. Here, we compared the operation of attentional templates during three-color and single-color search tasks. Preparatory template activation processes were tracked by measuring N2pc components to task-irrelevant singleton color probes that appeared in rapid succession during the interval between search displays. These probes attract attention (as indexed by an N2pc) if the corresponding color template is active at the time when the probe appears. In a three-color search task where target identity was fully predictable (Experiment 1), only probes that matched the upcoming target color triggered N2pcs, demonstrating that only a single target template was activated. When three possible color targets appeared randomly and unpredictably (Experiment 2), probes that matched any of these colors triggered N2pcs, demonstrating that all three templates were activated concurrently. However, relative to a single-color search task, clear costs emerged in this three-color task for attentional guidance toward search targets and for search performance. These costs appear to be linked to inhibitory interactions between simultaneously active search templates. These findings show that while at least three target templates can be maintained in parallel, multiple-template search is still subject to capacity limitations which affect both template-guided attentional guidance and the subsequent selective processing of search targets.