ACUTE EFFECTS OF CAFFEINE ON SELECTIVE ATTENTION AND VISUAL-SEARCH PROCESSES

The influence of a single dose of caffeine was evaluated in focused an d divided attention conditions of a visual selective search task in wh ich subjects had to perform controlled search processes to locate a ta rget item. Search processes were manipulated by varying display load. A dose of 3 mg/kg body weight caffeine or lactose, dissolved in a cup of decaffeinated coffee, was administered double blindly and deceptive ly to overnight abstinent coffee drinkers. Behavioral measures were su pplemented by event-related potentials (ERPs). Subjects reacted faster in the caffeine condition. The P3b peak latency decreased after caffe ine in the low display load condition and in the focused attention con dition, indicating that the effects of caffeine are dependent on the n umber of relevant display items, not on the total number of display it ems presented. Search processes, as reflected in a negative ERP deflec tion, were not affected by caffeine.