Influence of caffeine on information processing stages in well rested and fatigued subjects.

Examined the effects of caffeine on different information processing stages using choice reaction time (RT) tasks. A 200-mg dose at the beginning and a maintenance dose of 50 mg caffeine or lactose half-way through the session were administered to 15 well-rested and 15 fatigued university students (aged 18-25 yrs). Caffeine shortened RT. Event-related potential data indicate that caffeine increased cortical arousal and perceptual sensitivity. Stimulating effects of caffeine were mainly located at input and output stages of the information processing system. Fatigued Ss showed larger improvements in performance after caffeine than well-rested Ss. Results also indicate that caffeine effects were not stimulating in all Ss; 6 out of 30 Ss did not show arousing effects of caffeine.