Lou Lescuyer De Decker^1,2, Dirk Kerzel¹; ¹University of Geneva, ²University of Lausanne

The signal suppression hypothesis posits that the brain actively inhibits salient distractors to prevent attentional capture. While the distractor positivity (PD) is established as an electrophysiological marker of this suppression, its functional independence from target discrimination processes remains an open question. Adapting Drisdelle and Eimer (2021)’s paradigm, we orthogonally manipulated target (shape-defined) and distractor (color-singleton) presence in a visual search task, such that they never occupied the same axis. Participants had to enumerate targets across 4 sequential displays and then report how many they detected. To disentangle target and distractor processing, we contrasted displays where both target and distractor were present against displays where either target or distractor was absent. We hypothesized that isolating these components would reveal distinct electrophysiological signatures for capture (N2pc) and suppression (PD). Using a bootstrap-based approach adapted from Sawaki et al. (2012) we observed a comparable N2pc for all target-present conditions, regardless of distractor presence. Crucially, distractors elicited an early PD (105-224ms) in both target-present and target-absent conditions. Interestingly, this PD was larger in target-absent trials. Furthermore, it was consistently followed by a distractor-elicited N2pc (234-311ms). These findings support the existence of a rapid, active inhibitory mechanism that operates before attentional selection. However, the attenuated PD with concurrent target processing suggests that suppression efficiency is resource-dependent, resulting in less inhibition. The subsequent N2pc indicates that despite early inhibition, salient distractors still trigger delayed attentional orienting. To gather definitive evidence, we extended the paradigm to a multimodal setup combining EEG with frequency-domain fNIRS. We are currently running this protocol with the hypothesis that the PD will correlate with an enhanced activation in frontal inhibitory regions (anterior cingulate cortex and prefrontal cortex) and a reduced activity in the visual cortex contralateral to the distractor, confirming the inhibitory nature of this component.

Acknowledgements: This work is supported by the Swiss National Science Foundation (SNSF) grant n°10001_386.