Figure 3.

Relationship between evoked-saccade trajectories and the direction decision for monkey At (A–E) and Av (F–J). A, F, Average evoked-saccade vectors from individual sessions resulting from electrical microstimulation of the left (A) or right (F) FEF. B, G, Endpoints of evoked saccades from correct trials in a single session plotted relative to their running-mean values [to remove the effects of drift on the evoked-saccade trajectories and center the distributions of endpoints at zero, the location of the fixation point; see Materials and Methods and Gold and Shadlen (2000, 2003)] and separated by the subsequent voluntary choice (black points for leftward choices, gray for rightward choices). Solid line indicates the axis of motion. Dashed line indicates the optimal linear classifier for distinguishing between the two groups of points. C, H, Circular histogram of the distribution of the angle between the axis of motion and the optimal linear classifier separating evoked-saccade endpoints corresponding to the two direction choices for each session (the minimum angle between the solid and dashed lines in B and G). D, I, Magnitude of deviation versus session. Points and error bars are mean and SEM values, respectively, from correct (black symbols) or error (gray symbols) trials in individual sessions. Positive values indicate that evoked saccades tended to deviate in the direction of the monkey's subsequent choice. Filled symbols indicate H₀: magnitude = 0, p < 0.01 (Mann–Whitney test). Lines are weighted linear fits to data from correct trials only (H₀: slope = 0, p ≤ 0.05 in both panels). E, J, Ratio of the average magnitude of deviation measured on discrimination trials versus the average magnitude of deviation measured on instructed-saccade trials (which was not performed in all sessions). X marks indicate outliers that typically resulted from a near-zero denominator, plotted at outer bounds of −1 and 2. These points were not included in the linear fits (lines; H₀: slope = 0, p < 0.01 in both cases). pos, Position; deg, degree.