Electrophysiological Evidence of Semantic Interference in Visual Search

Telling, Anna L.; Kumar, Sanjay; Meyer, Antje S.; Humphreys, Glyn W. · 2009 · OpenAlex-citations

DOI: 10.1162/jocn.2009.21348

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Summary

This study investigates how semantically related distractors influence visual search, specifically examining whether such distractors interfere with early stages of attentional selection. While previous behavioral studies demonstrated that semantic relatedness between a target and a distractor slows reaction times and reduces accuracy, the temporal dynamics of this interference remained unclear. The authors sought to determine if semantic distractors affect early perceptual processing or later decision-making stages by analyzing event-related potentials (ERPs), with a primary focus on the N2pc component, which indexes attentional selection. The research comprised two experiments. Experiment 1 served as a behavioral baseline, where 12 participants searched for a target picture among a four-object display while maintaining fixation. The displays varied by target status (present/absent) and the presence of a semantically related distractor (same visual field, opposite visual field, or absent). Experiment 2 recorded EEG data from 18 participants using identical stimuli and procedures. The N2pc amplitude was calculated as the difference between contralateral and ipsilateral posterior electrode activity relative to the target or foil position. Behavioral results from both experiments confirmed that semantically related distractors disrupted search performance. Reaction times were significantly slower when a related distractor was present compared to when it was absent, particularly when the distractor appeared in the same visual field as the target. Accuracy was also affected, with more errors occurring when the distractor was in the opposite field. Crucially, the ERP analysis revealed that the presence of a semantic distractor modulated the N2pc component. The N2pc amplitude was most pronounced (largest negativity) when the target and the semantically related distractor were located in the same visual field. This amplitude was less pronounced when the distractor was in the opposite field or absent. Earlier components (P1 and N1), which reflect early perceptual processing, showed no significant differences across conditions. These findings provide electrophysiological evidence that semantic interference occurs during the early stages of attentional selection, rather than solely at later decision-making stages. The modulation of the N2pc suggests that semantic properties of distractors are extracted rapidly and compete for attention with the target template. The enhanced N2pc when the distractor shares the target's visual field indicates that the semantic distractor attracts attention to that location, creating competition for selection. This supports the view that top-down attentional templates can spread activation to semantically related items, influencing visual search efficiency through early neural mechanisms.

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• visual search