Oddball distractors demand attention: neural and behavioral responses to predictability in the flanker task.

Predictable and unpredictable distractors may differentially affect attention. We adapted the Eriksen flanker task by manipulating the probability with which specific flankers occurred. Subjects reported the orientation of briefly-presented targets while attempting to ignore four flanking items. Flankers had either standard (90% of trials) or oddball (10%) orientations. Congruent and incongruent configurations were equiprobable, as were target orientations. Oddball flanker orientations substantially enhanced congruency effects: performance was best when the target was congruent with oddball flankers and worst when it was incongruent. We recorded scalp EEG while subjects performed the task, and later computed ERPs timelocked to stimulus onset. Oddball flanker orientations evoked a visual mismatch negativity (vMMN). Subjects' temperament predicted individual differences in vMMN magnitude. Orientation sensitivity predicted larger vMMNs; attentional selectivity predicted smaller. Behavioral and vMMN results indicate that subjects exploit distractor predictability to support more-effective active inhibition; oddballs disrupt this strategy. Despite subjects' attempts to ignore the flankers, unexpected distractors strongly influence neural responses and behavioral performance.