The time course of distractor-based response activation with predictable and unpredictable target onset.

Electrophysiological recording in a temporal flanker task (i.e., distractors preceding the targets) has demonstrated that distractor processing is adjusted to the overall utility of the distractors. Under high utility, that is, distractors are predictive of the target/response, distractors immediately activate the corresponding response (as indicated by the lateralized readiness potential, LRP). This activation has been shown to be markedly postponed when the target predictably occurs delayed. To investigate the occurrence and time course of distractor-related response activation under conditions of unpredictable target onset, we randomly varied the stimulus-onset asynchrony (SOA) between distractors and targets and recorded the distractor-evoked LRP. When the distractor utility was high, an LRP occurred shortly after distractor presentation. In case of a long SOA the time course of this LRP was characterized by a drop back to baseline and a subsequent re-activation that reached a substantial level before target onset. These results suggest that distractor processing is characterized by sophisticated adjustments to experienced utility and temporal constraints of the task as well as by further control processes that regulate premature response activation.