Participants completed a flanker task with arrays of right- and left-facing arrows presented inside a horizontal rectangle. On compatible trials, flanker (peripheral) arrows faced in the same direction as the (central) target (i.e., →→→→→ or ←←←←←); on incompatible trials, flanker arrows faced in the opposite direction of the target (i.e., →→←→→ or ←←→←←). Compatible and incompatible arrays were presented pseudo-randomly, with the constraints that they occurred with equal probability and called for left- and right-hand responses equally often. Participants were instructed to respond to left-facing targets by pressing a button with their left index finger and to right-facing targets by pressing a button with their right index finger. The horizontal rectangle remained on the screen throughout the task, shown in black against a light gray (10% black) background. Targets were presented in dark gray (80% black). To strengthen flanker interference, the immediately surrounding arrows were slightly darker (90% black) and 10% larger than the targets, and the outermost flankers were even darker (100% black) and larger (20%) than the targets (see Ridderinkhof et al., 2002). Arrow arrays were presented for 100 ms.
