Caffeine, impulsivity, and memory scanning: A comparison of two explanations for the Yerkes-Dodson Effect

Two explanations for the Yerkes-Dodson Effect (1908) were tested. Easterbrook (1959) proposed that arousal reduces the range of cue utilization. Thus, arousal should interfere with the capacity for simultaneous (dual) memory scans. In contrast, Humphreys and Revelle (1984) proposed that arousal facilitates sustained information transfer but interferes with short-term memory. Arousal should thus reduce the time needed to prepare to respond but increase the time needed to scan memory. Either caffeine or placebo was given to 78 subjects who differed in impulsivity. They completed three versions of a memory-scanning task: two single-task versions (physical and category matches) and one dual-task version (either type of match). As predicted by Humphreys and Revelle, relative to placebo, caffeine lowered the intercept (p<.01), suggesting facilitation of sustained information transfer, but increased the slope (p<.05), suggesting impairment of access to short-term memory, of the regression of reaction time on log-transformed memory-set size. That caffeine had a main effect on slopes and on intercepts but did not interact with type of task suggests that arousal does not necessarily disrupt dual-task performance.