Pupillary correlates of preparatory control in the Stroop task.

In three experiments, individual differences in preparatory control in the Stroop task were examined. Participants performed variants of the Stroop task while pupillary responses were examined during the preparatory interval. Variation in working memory capacity was also examined. High Stroop performers tended to demonstrate larger preparatory pupillary responses than low Stroop performers. In Experiment 2, when participants were given pre-cues indicating the congruency of the upcoming trial (MATCHING vs. CONFLICTING), high Stroop performers had larger preparatory pupillary responses for incongruent trials compared to congruent trials, whereas low Stroop performers demonstrated similar preparatory pupillary responses on both incongruent and congruent trials. These results suggest that variation in Stroop performance is partially due to individual differences in the ability to ramp up and regulate the intensity of attention allocated to preparatory control processes. Additionally, there was limited evidence that preparatory control processes partially account for the relation between working memory capacity and performance on the Stroop. Overall, these results provide evidence that individual differences in Stroop performance are partialy due to variation in preparatory control.