Signal detection analysis was used to examine the effects of nicotine on a visual vigilance task. Groups of light, heavy and non-smokers performed the 80-min task on three separate occasions, and received different doses of nicotine each time. For all three types of smoker, nicotine significantly counteracted the decrement in stimulus sensitivity which occurred over time in the placebo condition, while having no effect on response bias. We argue that nicotine produced this effect by acting on the central, cholinergic pathways controlling electrocortical arousal, and therefore that these pathways play a role in the control of human information processing.