A mechanism for inhibition in visual search

Observers can use explicit foreknowledge of a feature of an upcoming target to guide search. However, little is known about observers' use of explicit foreknowledge that a specific feature will not match the upcoming target. In a series of experiments, we presented observers with either "ignore" cues that validly indicated the color of a nontarget item (rather than the color of the target item) in the upcoming display, or "neutral" cues. Surprisingly, observers unable to use "ignore" cues to speed search; instead, knowing the color of a nontarget item on the upcoming display slowed search. This cost for "ignore" cues compared to neutral cues was consistent across several experiments using several different types of "ignore" cues. We conclude that observers are unable to explicitly avoid selecting items appearing in to-be-ignored colors. Instead, we propose observers use a strategy of immediately selecting the irrelevant item in order to subsequently inhibit it.