Direct Evidence for Active Suppression of Salient-but-Irrelevant Sensory Inputs

Gaspelin, Nicholas; Leonard, Carly J.; Luck, Steven J. · 2015 · Psychological Science

DOI: 10.1177/0956797615597913

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Summary

This study addresses the long-standing debate regarding whether attentional capture by salient stimuli is purely stimulus-driven or goal-driven. The authors test the "signal-suppression hypothesis," a hybrid model proposing that while salient stimuli automatically generate a bottom-up salience signal, this signal can be actively suppressed via top-down control processes. To provide direct behavioral evidence for this suppression, the researchers developed a novel "capture-probe paradigm." This method allows for the measurement of processing resources allocated to specific locations in a visual array by having participants recall letters briefly superimposed on search items. The experimental design involved participants searching for a target shape among distractors while ignoring an irrelevant color singleton. On frequent search trials, participants identified the location of a dot within the target. On infrequent probe trials, letters appeared inside all shapes, and participants attempted to recall them. Experiment 1 validated the paradigm by using conditions known to promote attentional capture (searching for a shape singleton). Results showed that probe recall was significantly higher for letters inside the singleton distractor (26.6%) compared to nonsingleton distractors (14.7%), confirming that the singleton captured attention and drew resources away from the target. Experiment 2 manipulated the task to discourage singleton detection by requiring participants to search for a specific shape feature among heterogeneous distractors, a condition known to eliminate behavioral singleton-presence costs. Under these conditions, search response times were not slowed by the presence of the singleton. Crucially, probe recall for letters inside the singleton distractor (9.6%) was significantly lower than for letters inside nonsingleton distractors (15.4%). This "singleton-suppression effect" indicates that processing at the singleton location was actively inhibited below the level of nonsingleton items. The findings provide direct behavioral evidence supporting the signal-suppression hypothesis. The results demonstrate that when top-down goals allow it, the visual system actively suppresses the processing of salient-but-irrelevant stimuli, rather than merely failing to attend to them. This resolves the theoretical conflict by showing that capture is not an all-or-nothing phenomenon; instead, automatic salience signals can be overridden by active suppression mechanisms. This has significant implications for understanding attentional control, suggesting that effective visual search relies on the ability to inhibit distracting salient inputs, a process previously supported only by indirect electrophysiological data.

Key finding

When participants searched for a specific target feature, processing of irrelevant color singletons was actively suppressed below the level of nonsingleton distractors, as evidenced by reduced probe recall accuracy at the singleton location.

Methodology

lab_experiment

Sample size: 48

Provenance

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Topics

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• attention selective divided
• inattentional change blindness