Figure 1.

Schematic illustration of the task. A, Successive frames illustrate the sequence of stimulus presentations. Two stimuli were presented in sequence (S1 and S2), at either the same or diametric locations, followed by delay periods. After training, the second delay period was followed by two choice targets, and the monkeys were required to saccade to a green target if the two stimuli appeared at matching locations and to a blue target if they did not. In the pretraining stage, the animals were rewarded for maintaining fixation after the end of the second delay period. B, Stimulus set used for the analysis presented here.