Abstract
Contingent attentional capture refers to an involuntary shift of spatial attention toward an irrelevant stimulus for it resembles relevant stimuli that are important for achieving behavioral goals. Here, we investigated whether attentional capture can be elicited by stimuli that never reach conscious awareness. Subjects performed a delayed match-to-sample task, which involved maintaining a centrally presented color patch in working memory. After the delay period, subjects indicated whether a test stimulus had the same color as the sample stimulus. During the delay period, participants made a speeded response to a probe stimulus presented to either the left or right visual field. Just before the probe, however, a pair of colored distracters was presented in the same left and right visual field locations where the probe could appear. In some trials, one of these distracters had the same color as the sample stimulus being held in working memory while the other had a different color. We manipulated whether the distracters reached conscious awareness by changing their presentation duration and by applying meta-contrast masks. As in prior studies (e.g., Downing, 2000), in unmasked trials we observed contingent attentional capture. Specifically, response times were faster for probes that occurred in the same location as the same-colored distracter than for probes that occurred in a different location. Of importance, this effect was eliminated for masked stimuli. We conclude that irrelevant items resembling behaviorally-relevant stimuli involuntarily capture spatial attention, but only if the irrelevant items can be consciously perceived.
Supported by grants from NIMH (R01-MH60415) and NINDS (P01-41328, Proj. 2) to M.G.W.