Bias-free measure of distractor avoidance in visual search

Recent findings suggest that it is possible for people to proactively avoid attentional capture by salient distractors during visual search. The results have important implications for understanding the competing influences of top-down and bottom-up factors in visual attention. Nevertheless, questions remain regarding the extent to which apparently ignored distractors are processed. To assess distractor processing, previous experiments have used a probe method in which stimuli are occasionally superimposed on the search display-requiring participants to abort the search and identify the probe stimuli. It has been recently shown that such probe tasks may be vulnerable to decision-level biases, such as a participant's willingness to report stimuli on to-be-ignored items. We report here results from a new method that is not subject to this limitation. In the new method, the non-target search elements, including the salient distractors, contained features that were either congruent or incongruent with the target. Processing of the non-target elements is inferred from the effects of the compatibility of the shared features on judgments about the target. In four experiments using the technique we show that ignored salient distractors are indeed processed less fully than non-target elements that are not salient, replicating the results of earlier studies using the probe methods. Additionally, the processing of the distractors was found to be reduced at least in part at early perceptual or attentional stages, as assumed by models of attentional suppression. The study confirms the proactive avoidance of capture by salient distractors measured without decision-level biases and provides a new technique for assessing the magnitude of distractor processing.