Fig. 1.

Description of the sequence of events in the testing conditions. Instrumental Task Condition, This is a task state in which the monkey awaited the visual stimulus with its hand on the bar. Illumination of the light signaled the monkey to release the bar and reach for the target, which it had to touch to receive a liquid reward. Free Reward Condition, This is a no-task state in which the monkey remained motionless and received the same liquid reward in the absence of any external predictive signal. The present study used three versions of each behavioral situation. In the task state, the delivery of reward occurred immediately after contact with the target (Immediate) or was delayed after target contact by a constant 1 sec interval (Fixed Delay) or a randomly varying interval of 0.5–1.5 sec (Variable Delay). In the no-task state, liquid was delivered at irregular time intervals of 5.5–8.5 sec (Irregular) or at a constant interval of 4 sec (Regular 4-s) or 2 sec (Regular 2-s). In each of these two behavioral states, the various conditions were tested in separate blocks of trials.