Electrophysiological correlates of active suppression and attentional selection in preview visual search

Berggren, Nick; Eimer, Martin · 2018 · Crossref

DOI: 10.1016/j.neuropsychologia.2018.10.016

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Summary

This study investigates the neural mechanisms underlying "preview benefits" in visual search, where advance exposure to a subset of distractors improves search efficiency. While behavioral evidence for this effect is robust, the underlying processes—specifically whether previewed items are actively inhibited, maintained in working memory, or ignored—remain debated. The authors aimed to resolve this by examining electrophysiological correlates of distractor processing during the preview interval and subsequent attentional selection during the full search display. The researchers employed a lateralized preview search paradigm with 12 participants, using event-related potentials (ERPs) to track neural activity. Participants searched for a target defined by a color-shape conjunction in one visual hemifield while ignoring the other. On preview trials, distractors matching the target shape but not color were presented for 1000 ms before new items (including the potential target) were added. On no-preview trials, all items appeared simultaneously. The study measured lateralized posterior ERP components: the distractor positivity (PD) to assess inhibition of previewed items, and the N2pc and sustained posterior contralateral negativity (SPCN) to assess attentional selection during the full search display. Behavioral results confirmed significant preview benefits, with faster reaction times and fewer errors on preview trials compared to no-preview trials. Crucially, ERP data revealed a sustained contralateral positivity (PD) in response to preview displays, providing direct electrophysiological evidence that previewed distractors are actively inhibited rather than maintained in working memory or ignored. Analysis of the full search displays showed qualitative differences in attentional processing. On no-preview trials, an N2pc was elicited even when no target was present, indicating non-selective attentional allocation to all items on the relevant side. Additionally, an SPCN was observed on no-preview trials, suggesting reliance on working memory for target discrimination. In contrast, on preview trials, the N2pc was absent on target-absent trials, and the SPCN was entirely absent, indicating that attention was selectively allocated only to target objects and that discrimination occurred at early perceptual stages without requiring working memory maintenance. These findings support the visual marking hypothesis, demonstrating that preview benefits arise from the active top-down inhibition of previewed distractors. This inhibition allows for rapid, selective attentional allocation to new target objects, bypassing the non-selective attentional capture and working memory demands observed when all items are presented simultaneously. The study clarifies that preview effects are not merely due to temporal asynchrony or working memory templates, but are driven by specific inhibitory mechanisms that streamline subsequent visual processing.

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• visual search