This research describes 2 studies in which a computerized task was used to examine the influence of stimulants, sedatives, and fatigue on single-target and divided-attention responses in different parts of the visual field. Drug effects were evaluated over time with repeated behavioral/subjective measures against ascending and descending drug levels. In Study 1, subjects were given placebo, alprazolam, or dextroamphetamine (DEX). Alprazolam impairs performance, whereas DEX induces enhancement and tunnel vision. Study 2 exposed subjects to fatigue and no fatigue with a repeated-measures crossover design. Four independent groups subsequently received placebo, DEX, caffeine, or alcohol. Under fatigue, stimulants have no performance enhancing effects, whereas impairment from alcohol is severe. Under no fatigue, alcohol has a modest effect, caffeine has no effect, and DEX greatly enhances divided-attention performance coincident with tunnel vision. Subjects rate all drug effects more stimulating and less sedating while fatigued. Implications for transportation safety, and applications for research, are discussed.
Abstract