Fig 1.
Participants viewed an incentive array composed of an incentive star of one color and a non-informative star of another color (counterbalanced across participants). After ~1500 ms with only a fixation cross present, a visual search array composed of a circle and square appeared for 200 ms; both shapes were grey and contained a notch at the top or bottom. One shape served as target, the other as non-target (counterbalanced across participants). The task was to report as quickly and accurately as possible (by pressing the corresponding game pad button) whether the target’s notch was on the top or bottom. Points awarded for that trial and a running total were indicated on a feedback display seen for 500 ms. Points awarded (later exchanged for cash) were contingent on correct responses; crucially, the amount earned on each trial depended reliably on the color of the incentive star viewed on that trial. The location of the incentive star, target, and notch were randomized and unrelated to each other. Bilateral arrays were used to facilitate extraction of the N2pc and PD ERP components.