Attentional capture by a color singleton is stronger at spatially relevant than irrelevant locations: Evidence from an ERP study

Top-down spatial attention can modulate contingent attentional capture, but the underlying mechanism is still not clear. Using variants of spatial cueing paradigms, our previous event-related potential study showed that peripheral color singleton cues with task-relevant features captured attention (indexed by cue-elicited N2pc) even when the targets appeared at central locations, but the magnitude of attentional capture was smaller than when the targets appeared at same peripheral locations. One reasonable explanation is that the modulation effect is due to spatial relevance of cues. However, several other confounding factors might also explain the modulation effect, such as task difficulty, spread of attentional window, and inside/outside relation between cue and attentional window. In the present study, we rearranged the relative locations between cues and targets to control these factors and to further examine whether inequivalence of attentional capture across attended and unattended locations was a common phenomenon. In two experiments, color singleton cues elicited apparent N2pc components when participants were searching for targets possessing the same color, which replicated typical findings of contingent attentional capture. More importantly, the modulation effect of top-down spatial attention on the cue-elicited N2pc still existed even when the factors of task difficulty (Experiment 1), spread of attentional window (Experiment 1), or inside/outside relation between cue and attentional window (Experiment 2) were controlled. These results consistently demonstrate that attentional capture by a color singleton is stronger at spatially relevant locations than at spatially irrelevant locations, suggesting an important role of spatial relevance on contingent attentional capture.