Fig. 1.

A, Multi-target task. Along the top, the bars labeled “fixation,” “array on,” and “target dim” depict the temporal sequence of the multi-target task. The line below labeled “Eye” is a schematic of a representative eye position trace in this task. The lower portion of the figure depicts the spatial arrangement of the trial types. The large boxes are a schematic of the tangent screen. Thecross represents the fixation point, and the surroundingbox represents the criterion window for the monkeys to maintain eye position for correct task performance. Each of these trial types was randomly interleaved. As the number of possible targets (filled circles) increased, the probability that any one of them would be identified as the saccade target decreased. The fixation period began with the onset of a fixation point, followed by the pre-selection period when the array of possible stimuli came on. The selection period was the time when the target dimmed, and the initiation period was the time when the monkeys were given a cue to initiate the saccade, in this case, when the fixation point was removed. The temporal separation of events allowed the neuronal activity associated with each event to be dissociated.B, The blocked-mixed task. Along the top, the labeled bars indicate the temporal sequence of events in the task. Mixed target trials were those in which the saccade target was selected randomly on each trial from the eight stimuli. The blocked target trials were those in which the saccade target was always the one located in the movement field of the recorded neuron. Note that the time the target dimmed and the time the fixation point was removed occurred simultaneously, allowing the saccade to be initiated as soon as the target was selected.