The interactive effects of caffeine, impulsivity and task demands on a visual search task

Humphreys and Revelle (1983) have suggested that arousal hinders short-term memory processes but facilities attentional processes. In a conceptual replication of a study of body temperature and performance (Folkard et al., 1976), 84 undergraduates classified as low or high impulsive were given either caffeine or placebo. Two versions of a visual search task, one with a 2-letter target (a low memory load task) and one with a 6-letter target (a high memory load task), were used. As predicted, caffeine differentially affected the two tasks: subjects given caffeine detected a lower proportion of 6-letter targets but a greater proportion of 2-letter targets than did subjects given placebo. An unexpected interaction between Impulsivity, Task Sequence and Target Size suggested that high and low impulsives may have adopted different strategies or may have experienced different motvational states during the course of the experiment. The relevance of these data to Easterbrook's (1959) explanation of the Yerkes-Dodson effect is also discussed. These results are consistent with the assumption that there is an arousal dimension which is common to both caffeine and body temperature, and that this dimension is central to the observed pattern of performance.