Figure 1.

The sequence of events in an example trial of the behavioral task. The monkey is shown from above facing a video screen, and the monkey's fixation target is depicted by the converging dashed lines. a, The monkey fixated a light spot at the center of the screen. Then a gray circle appeared at one of four locations: right, up, left, or down from fixation (up depicted). The circle then revolved (curved arrow) around the fixation spot and stopped right, up, left, or down from fixation (right depicted), thus initiating the delay period (b). b, The monkey had to maintain central fixation while remembering the starting place of the circle and attending to its final location. c, After a variable delay period, the circle brightened (top) or dimmed (bottom) briefly (the go signal) and then disappeared. d, Brightening instructed a saccadic eye movement (white arrow) to the remembered location (top); dimming instructed a saccade to the attended location (bottom).