Figure 1. Behavioral task.

(a) Transition contingencies for the main task and the control task. Each target is denoted by a letter and drops indicate rewards. Optimal choices are denoted in bold. (b) The sensorimotor events on a representative trial. In each trial the monkeys made two eye movement decisions to obtain a reward. After initiating a trial by acquiring fixation the monkeys were shown the first pair of targets (randomly placed on either side of fixation) and, after a brief delay, chose one target by making a saccade to it. The monkeys then returned to fixation, were shown the second pair of targets and made their second choice. The trial ended with a final return to fixation and delivery of the final reward. The target sequence that delivered the largest reward was switched across trial blocks and the monkeys discovered this sequence by trial and error.