The mutations paradigm: assessing the time course of distractor processing

The temporal loci of distractor processing were assessed in a flanker task with mutating distractors. We introduce the mutations paradigm, which allows for behavioral assessments of the critical time window during which distractors are processed. A central target was flanked by two identical distractors. While the target remained unchanged throughout the trial, the distractors' identities mutated once per trial, at a random time during the initial 200 ms following onset. There were three types of trials: incongruent (i.e., disruptive) distractors that mutated to neutral distractors, neutral distractors that mutated to incongruent ones, or neutral distractors that mutated to different neutral distractors (control). The results revealed that presentations of incongruent distractors for a mere 17 ms were sufficient to significantly delay responses. After 50 ms, perceptual information ceased to be accumulated from distractors locations but was still being collected from the target location. We suggest that (a) extensive information about the target and distractors was gathered as early as 17 ms after onset; (b) attentional modulations of processing consummated later, between 34 and 51 ms; and (c) once attentional mechanisms had stepped in (~50 ms), selection achieved full and sustained efficiency. These findings seem to challenge basic assumptions held by early-selection, late-selection, and load theories.