Effects of bottom-up salience within the feature search mode

Recent research suggests that bottom-up salience determines attentional priority only when subjects adopt the strategy of searching for a discontinuity (singleton-detection mode). In contrast, bottom-up salience is held to play no role in visual search when subjects look for a known-to-be-relevant target feature (feature-search mode). This conclusion is based on the finding that within the feature-search mode, a singleton distractor captures attention to its location only if it possesses the target feature. However, in such studies, only top-down factors (whether or not the distractor possessed the target feature) were manipulated, while bottom-up factors were kept constant, as the distractor was always a singleton. Thus, while these findings suggest that salience has no effect on performance outside the attentional set adopted by the observer for a specific feature, it remains possible that salience may enhance attentional priority within this set. This question was explored in two experiments by investigating whether or not a distractor possessing the target feature is more difficult to ignore when it is a singleton (high bottom-up activation) than when it appears within a heterogeneous background (low bottom-up activation). A distractor possessing the target feature produced stronger capture when it was salient, but only early in processing. Moreover, a singleton distractor outside the attentional set was inhibited rather than simply ignored. These results suggest that bottom-up salience plays a role within the feature search mode, and that overriding capture by an irrelevant singleton results from inhibiting this singleton's salient feature rather than from ignoring salience per se.