Dock Duncan^1,2 (), Dirk van Moorselaar^1,2, Jan Theeuwes^1,2,3; ¹Vrije Universiteit Amsterdam, ²Institute for Brain and Behaviour, Amsterdam, ³William James Center for Research, ISPA-Instituto Universitario, Lisbon, Portugal

Recent advancements in understanding visual search dynamics have illuminated the complex interplay between attentional selection and distractor processing. A key finding is the divergent mechanisms by which the brain handles salient distractors across different search modes, with interference patterns dramatically shifting between parallel and serial visual search conditions. While previous research has established distinct patterns of distractor processing across search modes—with high salient distractors interfering more in parallel search and being more efficiently ignored in serial search—the underlying neural mechanisms remain unclear. Specifically, whether the observed discrepancy should be attributed to proactive or reactive mechanisms remains unresolved. To investigate this, we relied on lateralized event-related potentials, the N2pc and the Pd that index attentional selection and distractor processing respectively. In a series of EEG experiments, using different variations of the additional singleton paradigm we systematically varied search dynamics and distractor salience across three levels (low, medium, and high) to unpack these critical issues. Participants performed search tasks with distractors ranging from low to high salience across both parallel (Experiment 1) and serial (Experiment 2) search conditions. At the behavioral level, we replicated the established pattern: in parallel search, distractor interference scaled linearly with its salience, while in serial search, the scaling pattern was reversed, with high salient distractors leading to faster search times compared to low salient distractors. Critically, our encephalographic analysis demonstrated that both early and late phases of the Pd component were systematically modulated by distractor salience, with distinct patterns across search modes. These neural-behavioral findings converge to challenge the predominant paradigm that distractors are proactively suppressed in serial search tasks, motivating a reevaluation of how we study distractor suppression. Furthermore, these results provide additional insight into the use of variable latency of the widely used distractor positivity component to dissociate between proactive and reactive mechanisms.

Acknowledgements: ERC grant (833029 - LEARNATTEND) and NWO grant (406.21.GO.034)