Attentional capture is modulated by stimulus saliency in visual search as evidenced by event-related potentials and alpha oscillations

Forschack, Norman; Gundlach, Christopher; Hillyard, Steven A.; Müller, Matthias M. · 2022 · OpenAlex-citations

DOI: 10.3758/s13414-022-02629-6

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Summary

This study investigates how stimulus saliency modulates attentional capture in visual search, addressing the ongoing debate regarding the role of bottom-up salience versus top-down control. Specifically, the authors examined whether the relative saliency of distractors affects attentional capture and how this is reflected in electrophysiological markers, particularly the distractor positivity (Pd) component and alpha-band oscillations, which are proposed neural signatures of distractor suppression. The researchers employed a four-item additional singleton paradigm with two participant groups. The Salient Target (ST) group searched for a salient orange square target among green fillers, with a non-salient green diamond distractor. The Salient Distractor (SD) group searched for a non-salient green diamond target among green fillers, with a salient orange square distractor. Electroencephalography (EEG) was recorded to measure event-related potentials (ERPs) and alpha-band activity. The design included trials where targets and distractors appeared together or alone, allowing for the assessment of competitive interactions. Behavioral results indicated that reaction times were faster for the ST group, demonstrating that salient targets facilitate processing. Crucially, the salient distractor in the SD group caused significant behavioral interference (slower reaction times), whereas the non-salient distractor in the ST group did not, indicating that attentional capture occurred only for the salient distractor. Electrophysiologically, the N2pc component, indexing target attention, had a shorter latency for salient targets. Contrary to the signal suppression hypothesis, which predicts that the Pd reflects proactive suppression of distractors, both salient and non-salient distractors elicited Pd components of equal amplitude. Furthermore, the Pd amplitude was greater when distractors were presented alone than in competition with targets, challenging the view that the Pd requires competitive interactions. Alpha-band analysis revealed event-related desynchronization during target processing but showed no significant amplitude enhancement contralateral to distractors, regardless of their saliency. These findings suggest that top-down guidance of attention can be offset by relative stimulus saliency, leading to attentional capture by salient distractors. The results argue against the Pd serving as an index of proactive distractor suppression, as it appeared even when distractors were not suppressed behaviorally. Instead, the data support independent neural mechanisms for target and distractor processing, implying that bottom-up salience plays a critical role in visual search that cannot be entirely overridden by top-down control in small-set displays.

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Topics

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• attention selective divided
• visual search