Salient‐but‐irrelevant stimuli cause attentional capture in difficult, but attentional suppression in easy visual search

Barras, Caroline; Kerzel, Dirk · 2017 · Crossref

DOI: 10.1111/psyp.12962

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Summary

This study investigates how visual search difficulty influences the processing of salient-but-irrelevant distractors, specifically addressing whether such stimuli cause attentional capture or suppression. The authors utilized the additional singleton paradigm, where participants searched for a target defined by one feature dimension (e.g., shape) while ignoring a distractor defined by another (e.g., color). Search difficulty was manipulated by varying the similarity between the target and nontarget items: high similarity (target square among diamond nontargets) created difficult searches, while low similarity (target square among circle nontargets) created easy searches. The research aimed to resolve conflicting findings in prior literature regarding whether irrelevant distractors capture attention or are suppressed, hypothesizing that search efficiency determines the outcome. The study comprised two experiments using electroencephalography (EEG) to measure electrophysiological correlates of attention. In Experiment 1, participants searched for a shape singleton target while ignoring a color singleton distractor. In Experiment 2, the roles were reversed: participants searched for a color singleton target while ignoring a shape singleton distractor. This design allowed the researchers to control for potential differences in the inherent saliency of color versus shape features. Behavioral performance was measured via reaction times, while EEG data focused on lateralized components: the N2pc (indicating attentional selection/capture), the PD (indicating attentional suppression), and the Ppc (an early positivity reflecting bottom-up saliency signals). Results from Experiment 1 demonstrated that interference from the color distractor was significantly stronger during difficult searches (high target-nontarget similarity) than during easy searches. Electrophysiologically, difficult searches elicited an N2pc to the distractor, confirming attentional capture. In contrast, easy searches elicited a PD to the distractor, indicating attentional suppression. Furthermore, the early Ppc component occurred only during easy searches when the distractor was unlikely to be selected, suggesting that attentional requirements modulate this early saliency signal. Experiment 2 replicated these findings when the target and distractor dimensions were swapped, confirming that the effects were driven by search difficulty rather than the specific perceptual features involved. The findings conclude that attentional suppression of salient-but-irrelevant distractors is only possible when visual search is efficient. When search is difficult due to high target-nontarget similarity, attention is captured by the most salient stimulus regardless of task relevance. This supports models suggesting that top-down goals can suppress distractor signals only when the target is sufficiently distinct. The study also clarifies the functional role of the Ppc component, linking its occurrence to conditions where the salient stimulus is not selected, thereby refining the understanding of early visual processing stages in attentional control.

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Topics

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• visual search
• attention selective divided