Electrophysiological Evidence of the Capture of Visual Attention

Hickey, Clayton; McDonald, John J.; Theeuwes, Jan · 2006 · OpenAlex-citations

DOI: 10.1162/jocn.2006.18.4.604

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Summary

This study investigates whether salient, task-irrelevant stimuli automatically capture visual attention, addressing a longstanding debate between automatic capture theories and contingent capture hypotheses. While behavioral data often show response time costs when irrelevant singletons are present, it remains unclear if this reflects automatic attentional shifts or increased perceptual filtering costs. To resolve this, Hickey, MacDonald, and Theeuwes utilized event-related potentials (ERPs), specifically the N2pc component, which indexes the spatial deployment of attention. The N2pc allows for the direct observation of attentional shifts to both targets and distractors, overcoming the limitations of behavioral measures that only reflect processing of task-relevant items. The researchers conducted two experiments using a visual search paradigm. Participants viewed circular arrays containing a target singleton defined by shape and, on some trials, a more salient distractor singleton defined by color. The primary goal was to detect an N2pc elicited by the distractor, which would indicate automatic attentional capture. Experiment 1 employed a design where the distractor and target were never presented on the same side of fixation, potentially allowing participants to use the distractor as a cue for the target’s location. Experiment 2 modified this design by including trials where the distractor and target appeared on the same side, thereby ruling out voluntary search strategies based on hemifield cues. EEG data were recorded from multiple electrodes, and ERPs were analyzed to measure the latency and amplitude of the N2pc relative to lateralized stimuli. The results provided strong electrophysiological evidence for automatic attentional capture. In Experiment 1, a distractor-elicited N2pc was observed when the distractor was lateralized and the target was on the vertical meridian, indicating that attention was initially oriented to the irrelevant stimulus. However, the absence of a clear polarity reversal in contralateral conditions suggested potential strategic influences. Experiment 2 confirmed these findings while controlling for strategy; both the distractor and target elicited N2pc components when presented on opposite sides of the array. Crucially, the distractor-elicited N2pc preceded the target-elicited N2pc, demonstrating that attention shifted to the salient distractor before being reoriented to the target. Behavioral data supported these findings, showing significantly slower response times and higher error rates when the distractor was present. These findings support the theory that stimulus-driven control plays an integral role in visual attention, even when stimuli are irrelevant to current goals. The study demonstrates that highly salient distractors automatically capture attention, causing a delay in target processing. This provides direct neural evidence against the contingent capture hypothesis, which posits that irrelevant stimuli can be effectively ignored if they differ in feature dimension from the target. Instead, the results indicate that attention is involuntarily drawn to salient events, requiring a subsequent shift to the task-relevant target. This has significant implications for understanding the mechanisms of selective attention and the interaction between bottom-up salience and top-down goals.

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Topics

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• attention selective divided
• inattentional change blindness
• visual search