Electrophysiological indices of distractor processing in visual search are shaped by target expectations

van Moorselaar, Dirk; Huang, Changrun; Theeuwes, Jan · 2022 · Crossref

DOI: 10.1101/2022.12.21.521409

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Summary

This study investigates the neural mechanisms underlying distractor suppression in visual search, specifically addressing whether the distractor positivity (PD) component of event-related potentials (ERPs) reflects pure proactive suppression or is also influenced by the upweighting of target features. While the signal suppression hypothesis posits that salient distractors can be actively inhibited, previous research has largely ignored how regularities in target features across trials might shape these electrophysiological indices. The authors aimed to disambiguate whether the PD is solely a marker of distractor inhibition or if it partially reflects the enhancement of predictable target features. To test this, the researchers conducted an experiment with 24 participants using a visual search paradigm combined with EEG recording. Participants searched for a target shape (cued by a fixation marker) embedded in a heterogeneous display of shapes. The study manipulated target feature regularity across two conditions: a "fixed-features" condition, where target shape and color remained constant across trials, and a "mixed-features" condition, where target shape and color varied randomly. A salient color singleton distractor was present in some trials. The experimental design allowed for the independent assessment of target selection (measured by the N2pc component) and distractor processing (measured by the PD component) under conditions of high versus low target predictability. Behavioral results showed that target selection efficiency was unaffected by the manipulation; participants exhibited a reliable singleton-presence benefit in both fixed and mixed conditions, with no significant differences in response times or accuracy. Electrophysiologically, the N2pc component, which indexes covert attention to the target, remained stable in amplitude and time course regardless of whether target features were fixed or varied. However, the PD component elicited by distractors was significantly attenuated in the mixed-features condition compared to the fixed-features condition. Although the PD remained statistically reliable in the mixed condition, its amplitude was reduced, indicating that the neural signature of distractor processing is sensitive to the predictability of target features. The findings demonstrate that the distractor PD cannot be unequivocally attributed to proactive suppression alone. Instead, the PD reflects a combination of distractor suppression and the upweighting of target features. When target features are unpredictable, the upweighting mechanism is diminished, leading to a reduced PD. This challenges the interpretation of the PD as a pure index of suppression and highlights the critical role of selection history and target expectations in shaping electrophysiological markers of attention. The study implies that future research on attentional capture must account for the interplay between suppressive mechanisms and target feature enhancement to accurately interpret neural data.

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Topics

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• visual search
• attention selective divided