Fig. 2.

Decreased target probability reduced buildup neuron activity. The events of the task are indicated by the labeled periods across the top, and the spatial arrangement is indicated by the schematic of the tangent screen as drawn in Figure 1. The eye position trace is a schematic. This example is from trials when the stimulus that fell in the movement field of the neuron was identified as the target. The left columnshows rasters and the average spike density function for five trials during the pre-selection period when one (A), two (B), four (C), or eight (D) possible targets were presented. Thearrowheads and the vertical dashed linesindicate the alignment of the traces. The left column is aligned on the onset of the possible targets, and themiddle column is aligned on the beginning of the selection period, when one of the stimuli dimmed. Both the initial visual and the delay period responses decreased as the number of stimuli increased. Activity increased after the stimulus in the movement field dimmed, indicating it was the target (dashed vertical line in the middle column). Theright column is aligned on the onset of the saccade, the initiation period. This neuron had a burst of action potentials associated with the onset of the saccade that did not differ between the probability conditions.