INFLUENCE OF CAFFEINE ON SELECTIVE ATTENTION IN WELL-RESTED AND FATIGUED SUBJECTS

Effects of caffeine were studied in a visual focused selective search task in well-rested and fatigued subjects. A dose of 200 + 50 mg caffe ine or placebo, dissolved in decaffeinated coffee, was administered in a double-blind and deceptive fashion. The task was to detect a target letter on one diagonal of a visual display designated as relevant and ignore stimuli presented on the irrelevant diagonal. Behavioral measu res were supplemented by event-related potential (ERP) measures. Subje cts reacted faster in the caffeine condition. Caffeine enhanced the N1 and the N2b components. Selection of relevant information apparently was more adequate in this condition. Search negativity was not affecte d by caffeine. Caffeine effects on the P3 elicited by target letters w ere more pronounced in the fatigued than in the well-rested subjects, indicating that the effects of caffeine are dependent on the state of the subject. The results suggest that caffeine has specific rather tha n general effects on information processing.