Fig 1.

Experimental paradigm. Subjects responded to single color letters by pressing response buttons held in each hand. Letters were successively presented every 2.5 s (duration 1.5 s) in triplets separated by 5 or 9 s. Triplets were constructed to vary task repetition, switching, and recency within the three-letter sets (ABA, ABB, and ABC, where A, B, and C reflect task order within a triplet, but can indicate any of the three tasks). Indicated are three particular examples of the triplets ABB, ABC, and ABA.