Knowing what not to look for: Difficulty ignoring irrelevant features in visual search

Foreknowledge of target-relevant information can be used to guide attention in visual search. However, the role of ignoring in visual search - that is, having foreknowledge of information related to nontargets - remains relatively unexplored. In a recent paper, Munneke et al. (2008) demonstrated that participants could ignore the location of an upcoming distractor if that location was cued prior to the display. In a series of experiments using a similar design, we explored whether participants could ignore a specified feature. Participants were asked to identify which of two possible uppercase letters was present in a display consisting of four differently colored letters. On “Distractor-Cued” trials, participants were also told that the target would not be a specific color (e.g. “ignore red”). Participants were unable to successfully use these cues to speed search - in fact, they were slower to find the target on Distractor-Cued Trials even though the cue contained relevant information and was 100% valid. We also measured compatibility effects of the cued distractor (a lowercase letter either compatible or incompatible with the target). There were stronger compatibility effects on Distractor-Cued Trials later in the experiment, suggesting that participants were not learning to suppress the irrelevant feature. Taken together, these data suggest that while knowing where not to look facilitates visual search (Munneke et al., 2008), knowing what not to look for hinders visual search. In subsequent studies we show that while establishing an attentional set to ignore a feature prior to a given trial results in less efficient visual search, if a set is established, search can be more efficient when the to-be-ignored feature appears than when it doesn't. This is consistent with Woodman and Luck's (2007) “template for rejection.” Ongoing experiments are investigating whether there are cases for which knowing what feature to ignore facilitates visual search.