INFLUENCE OF CAFFEINE ON INFORMATION-PROCESSING STAGES IS WELL RESTEDAND FATIGUED SUBJECTS

The effects of caffeine on different information processing stages wer e examined by using choice reaction time tasks. Independent variables were stimulus degradation, stimulus-response compatibility, time-uncer tainty, state of the subject, and caffeine treatment. The task variabl es were assumed to affect the following processing stages; encoding, r esponse selection and motor preparation, respectively. A 200 mg dose a t the beginning of the experiment and a maintenance dose of 50 mg caff eine or lactose half-way through the session were administered to well rested and fatigued subjects, double-blind and deceptively. Behaviour al measurements, event-related potentials (ERPs) and mood questionnair es were used to assess caffeine effects. The data showed that caffeine shortened reaction time. This effect showed an interaction with stimu lus degradation and time uncertainty. In addition, ERP results support ed the view that caffeine increases cortical arousal and perceptual se nsitivity. Stimulating effects of caffeine were mainly located at inpu t and output stages of the information processing system. Central proc esses were unaffected by caffeine. Fatigued subjects showed larger imp rovements in performance after caffeine than well-rested subjects. The results also indicated that caffeine effects were not stimulating in all subjects: 6 out of 30 subjects did not show arousing effects of ca ffeine.