Interactions of alcohol and caffeine on human reaction time.

Eight naive subjects (4 males and 4 females) took part in an experiment to investigate the direction of the interactive effects of alcohol and caffeine on reaction time. Subjects were tested under each of four conditions on separate occasions: no alcohol + no caffeine; no alcohol + caffeine; alcohol + no caffeine; and alcohol + caffeine. Alcohol was given in the form of 65.5 degrees proof vodka in the quantity of 2.2 ml/kg body weight; caffeine was given in the form of crushed 150-mg tablets in decaffeinated coffee. Under these conditions the experiment demonstrated that caffeine has a synergistic interaction with alcohol. Furthermore, using Sternberg's (37) additive-factor method, it was shown that the effects of both alcohol and alcohol + caffeine occur mainly at the peripheral stages of information processing (i.e. at the stimulus input and response output) rather than centrally.