Psychomotor vigilance task performance. (A) Testing lapse 400 during the placebo study visit was increased from training lapse 400 (P = 0.036). Testing lapse 400 during the dexmedetomidine study visit was also increased from training lapse 400 (P = 0.009). There was no statistically significant difference in testing lapse 400 between groups after controlling for training lapse 400 (P = 0.281). (B) The average testing reaction time during the placebo study visit was increased from the average training reaction times (P = 0.012). The average testing reaction time during the dexmedetomidine study visit was also increased from the average training reaction time (P = 0.014). There was no statistically significant difference between the average testing reaction times between groups after controlling for the average training reaction times (P = 0.295).