A unitary focus of spatial attention during attentional capture: Evidence from event-related brain potentials.

We studied whether attentional capture in vision can be elicited simultaneously at multiple locations in the visual field or whether it is always restricted to a single location. Participants searched for color singleton targets in search arrays that were preceded by spatially uninformative color cue arrays. Single cue arrays contained a unique color singleton among gray background items, and double cue arrays included two different-colored objects. Behavioral spatial cueing effects and N2pc components indicative of attentional capture were triggered by single as well as double cue arrays, but these capture effects were smaller with double cues. Response latencies were used to distinguish double cue trials where attention was captured by a left or right cue and trials where it was attracted by a cue on the vertical meridian. The N2pc was only present on horizontal capture trials, indicating that attentional capture is not triggered in parallel and equally at different locations, but is strongly weighted towards one object and one location at a time. Results show that when multiple salient visual objects compete for attentional selection, the capacity of each object to capture attention is reduced, but the focus of spatial attention tends to remain unitary.