 2.2 Caffeine. As in previous studies investigating the effects of caffeine on electrophysiological measures, in each session participants will be asked to swallow with water one of two identical pill capsules containing either caffeine 200 mg or placebo. This method and dosage were selected as oral administration of caffeine results in efficient absorption, while the intermediate size dose, which is typical of most studies of caffeine on cognition, has been shown to exert widespread, strong cerebral effects. Furthermore, administration of caffeine in pill form allows for greater control over dosage and facilitates double-blind procedures, while controlling for potentially confounding sensory effects e.g. smell, taste of coffee. 