CAFFEINE AND SELECTIVE VISUAL PROCESSING

This work addressed five issues: a) Does caffeine modulate electroence phalogram (EEG) background activity in a manner consistent with the id ea of cortical ''arousal''? b) Is performance in a simple speeded task improved under caffeine? c) Is visual processing more selective under caffeine? d) Does caffeine affect sensory discrimination? and e) Does it affect motor processes? We presented 16 subjects with a visual sel ection task under conditions of either caffeine or placebo. Background EEG data, gathered before administration of the task, revealed that c affeine resulted in lower slow-or power, relative to placebo, which is consistent with the idea of increased cortical ''arousal.'' During th e selection task, subjects had to respond manually to a given target c onjunction of spatial frequency and orientation. Other conjunctions sh ared spatial frequency, orientation, or neither with the target. The f our conjunctions were presented in a random sequence, with SOAs rangin g between 750 and 950 ms. Event-related potentials (ERPs) to the conju nctions were recorded at standard scalp locations Fz, Ct, Pt, and Oz. Under caffeine, subjects made faster responses to target conjunctions (382.9 vs. 404.5 ms) and more hits, whereas the false-alarm rate was e qual across conditions. Caffeine did not affect the selection potentia ls normally obtained in this task, by subtracting, from ERPs to nontar gets with the target spatial frequency, those to nontargets with the o ther frequency. However, an early differential positivity (50-160 ms) was found specifically under caffeine, indicative of increased selecti vity. Difference ERPs as a function of physical parameters were not af fected by caffeine, indicating no effect on sensory discrimination. On sets of response-related lateralizations above the motor cortex were n ot affected by caffeine, suggesting that the shorter reaction times un der caffeine were due to faster central or peripheral motor processes.