Effects of amphetamine and barbiturate in a serial reaction task under paced and self-paced conditions.

Effects of drug conditions (barbiturate, amphetamine, placebo) were investigated in a serial choice RT-task under three pacing conditions: self-paced, paced-fast (approx. 3 signals/sec) and paced-slow (approx. 1 signal/sec). Drug treatment and pacing condition were varied in a factorial design with 9 male Ss. Drugs affected the reaction time but not the error scores. Barbiturate slowed down RT and this effect was most prominent in paced-fast. Amphetamine, on the other hand, speeded up the RT but it had no effect in paced-fast. To account for these differential effects of the two drugs, it was postulated that barbiturate counteracts the arousing effect of time pressure whereas amphetamine speeds up reaction when the task is not arousing. This is consistent with Trumbo and Gaillard (1975) but it contradicts predictions derived from a theory by Broadbent (1971).