All plots compare measurements in congruent (red labels and markers) versus incongruent conditions (blue labels and markers). (a) Endpoints of saccades to a stimulus located at (10, 0) collected during a single session from monkey G. The origin corresponds to the average saccade endpoint. For each data point, the displacement is the distance to the origin. Yellow circles indicate 1 and 2 SDs in displacement from the congruent data. (b) Mean normalized displacement in each experimental session (). Displacement values for each session were z-scored, and then congruent and incongruent trials were averaged separately. Colors indicate monkeys (G, gray; K, white). The session shown in (a) is marked by the green cross. (c) Mean normalized displacement for each monkey, averaged across sessions. Error bars indicate 1 SE. (d) Average time course of eye velocity for saccades to stimuli at (8, 4) collected during a single session from monkey K. Inset zooms in on the change in peak velocity of /s between congruent (red, trials) and incongruent (blue, trials) trials. Shades indicate 1 SE across trials. (e) Mean peak velocity in each experimental session. Colors indicate monkeys (G, gray; K, white). The session shown in (d) is marked by the green cross. (f) As in (e) but for saccade amplitude. (g) Average velocity (top) and amplitude (bottom) values averaged across sessions and monkeys. Error bars indicate 1 SE. All significance values are for differences in means across experimental conditions, from permutation tests for paired data. The results indicate that saccades to high-reward locations are spatially more precise (a–c) and have higher peak velocities (d, e, g) than those to low-reward locations, whereas saccade amplitude changes little in comparison (f, g). Results are consistent with earlier reports (Lauwereyns et al., 2002; Takikawa et al., 2002; Watanabe and Hikosaka, 2005).