An electrophysiological study of attention capture by salience: Does rarity enable capture?

Abstract

Several behavioural studies have suggested that rarity is critical for enabling irrelevant, salient objects to capture attention. We tested this hypothesis using the N2pc thought to reflect attentional allocation. A cue display was followed by a target display in which participants identified the letter in a specific colour. Experiment 1 pitted rare, irrelevant abrupt onset cues (appearing on only 20% of trials) against target-relevant colour cues. The relevant colour cue produced large N2pc and cue validity effects even when competing with a rare, salient, simultaneous abrupt onset. Similar results occurred even when abrupt onset frequency was reduced to only 10% of trials (Experiment 2). Experiment 3 examined rare, irrelevant colour singleton cues (20% of trials). Despite being rare and salient, these singleton cues produced no N2pc or cue validity effect indicating little attentional capture. Experiment 4 greatly increased colour cue salience by adding four background boxes, increasing colour contrast and tripling the cue display duration (from 50 to 150 ms). Small cue validity and N2pc effects were obtained, but did not strongly depend on degree of rarity (20% vs. 100%). We argue that rarity by itself is neither necessary nor sufficient to produce attention capture.