Effects of caffeine, practice, and mode of presentation on stroop task performance

A series of experiments were designed to investigate the effects of 125 and 250 mg caffeine, or placebo, on performance of the Stroop task. Caffeine had no effect on performance of either the classic colour-word version or a numerical version of the task, either using computerised presentation of the stimuli or a traditional card version. However, significant practice effects were found using a within-subjects design with the card version of the task, and differences were found between performance in the card and computerised versions of the task. It is concluded that at these doses, caffeine does not significantly affect Stroop performance. It is also suggested that practice effects in studies using within-subject designs may be a problem when attempting to detect subtle effects of drugs on cognitive performance, and that the computerised version of the Stroop task may not be an exact analogue of the traditional card version.