Dose-dependent effects of oral administration of MHP on cognitive task performance. A, Error rates (±SEM) for the delayed response task. n = 19, 10, 11, and 12 (for Monkey M, it was 9, 5, 5, and 4 and, for Monkey J, it was 10, 5, 6, and 8), respectively, for the doses of 0, 1, 2, and 5 mg/kg MPH. B, Error rates (±SEM) for the go/no-go task. C, No-go specific error rates (±SEM) for the go/no-go task. For both B and C, n = 15, 10, 9, and 10 (for Monkey M, it was 8, 5, 5, and 5 and, for Monkey J, it was 7, 5, 4, and 5), respectively, for the doses of 0, 1, 2, and 5 mg/kg MPH. D, Response rate (±SEM) for each key in the self-control task. Each color indicates the number of plus marks within the target, the number of which indicated both the magnitude of the reward and the waiting time until reward delivery. n = 15, 16, 13, and 11 (for Monkey M, it was 7, 8, 6, and 6 and, for Monkey J, it was 8, 8, 7, and 5), respectively, for the doses of 0, 1, 2, and 5 mg/kg MPH. Statistically significant differences are indicated: †p < 0.01, ‡p < 0.005, and §p < 0.001.