Figure 1.

Stimuli and procedure. (a) Stimuli used in the experiment and conditions in a 2 × 2 factorial design. Cognitive load (low load vs. high load) was manipulated by varying the ratio of arrows pointing to the same direction (3:0 vs. 2:1). Surprise level (standard vs. oddball) was manipulated by varying probabilities of two types of arrows (smaller and larger) that were irrelevant to the task (80% standard trials vs. 20% oddball trials). The size of the oddball arrows were counterbalanced across runs and participants. (b) A schematic description of a standard and an oddball trial. Each trial began with the presentation of three arrows for a fixed duration of 250 ms, followed by 1750 ms blank screen, during which participants indicated the direction of the majority of the arrows.