A Rapid Effect of Caffeinated Beverages on Two Choice Reaction Time Tasks

Abstract

Though consumers of tea and coffee can report feeling beneficial subjective effects of consumption virtually immediately, tests for objective effects of caffeine immediately post-consumption have been rare. Two experiments examined caffeine's ability to influence reaction time in choice reaction time tasks, using a dose of caffeine typical of a cup of tea or instant coffee, and testing at short post-consumption delays. Two groups of participants were given 60 mg of caffeine, after overnight abstinence, either in a hot tea drink, or a hot water drink. Two control groups also received hot tea or water, but without caffeine. In Experiment 1, participants were given a keypress task before the drink (baseline), immediately after the drink, and 40 min after the drink. In Experiment 2, a touch-screen test was given either 1, 14, or 27 min post consumption. Caffeine was found to reduce the effect of a distracter on reaction time in the keypress test and to reduce reaction time in a component of the touch-screen task; however, in neither experiment were these effects significantly modulated by post-consumption delay length. Thus, the speed of caffeine's action on psychomotor performance was shown to be on the order of minutes.