Statistical context learning in visual search: distinct electrophysiological signatures of contextual guidance and context suppression

Facilitation of visual search by repeated distractor contexts is typically studied employing distractor configurations that are 100% predictive of the target location. Yet, real-world contexts vary in predictivity. We used electroencephalography (EEG) in human participants of either sex to explore how visual search facilitation arises from two distinct processing modes-contextual guidance and context suppression-that depend on the predictivity of distractor contexts, comparing repeated distractor arrangements that were either predictive or nonpredictive of target location against a baseline of nonrepeated arrangements. In Experiment 1, we manipulated context predictivity by shifting repeated contexts from predictive to nonpredictive and vice versa, while in Experiment 2, we restricted repeated contexts to one side of the display to assess lateralized effects of the two processing modes. Both types of contexts behaviorally facilitated visual search, but facilitation was larger with predictive contexts. Making predictive contexts nonpredictive reduced the facilitation while rendering nonpredictive contexts predictive failed to produce gains. Half-display predictive contexts facilitated target detection on both sides, while nonpredictive contexts facilitated same-side target detection only. EEG analyses revealed that predictive contexts triggered an early N1pc (guidance signal), followed by an enhanced N2pc (attentional selection) and an increased contralateral delay activity (CDA, indexing working memory processing of the target) in occipitoparietal regions, indicative of contextual guidance boosting the entire processing chain. In contrast, nonpredictive contexts produced only an increased N2pc accompanied by reduced CDA, consistent with context suppression. These differential patterns demonstrate contextual guidance and context suppression to operate as electrophysiologically distinct processing modes.