5-HTP increases intertrial initiation time, constricts the pupil, and increases reaction time with concomitant changes in performance. A, Left, 5-HTP increased the amount of time monkeys took before initiating a trial (mean ± SEM; individual session data are overlaid with data from each monkey using different shapes). Right, The percent changes in the intertrial initiation time were correlated with the percent changes in performance because of 5-HTP. B, Left, 5-HTP constricted the pupil (same format as in A, left). Right, The percent changes in pupil constriction were correlated with the percent changes in performance because of 5-HTP. C, Left, 5-HTP increased reaction time (same format as in A, left). Right, The percent changes in reaction time were correlated with the percent changes in orientation trial performance because of 5-HTP. Saline sessions are shown in blue, whereas 5-HTP sessions are shown in green. Each shape represents data from individual monkeys. *p < 0.05, ***p < 0.001, t test. The green lines in the scatter plots (A–C) illustrate linear regression fits.