Effect of caffeine on performances of a perceptual-restructuring task at different stages of practice.

Caffeine, a sympathomimetic drug which stimulates the adrenergic nervous system, was hypothesized to exert opposite effects upon performances of a perceptual-restructuring task (the Embedded Figures Task) at different stages of practice. Specifically, caffeine was hypothesized to impair performances of perceptual-restructuring tasks when the task is still novel in early trials; and to facilitate practice induced gains in task performance as the task becomes less novel. Sixty male undergraduates were studied. Each subject was tested on the Embedded Figures Task twice, in one of the following three sequences: caffeine-placebo; placebo-caffeine; and placebo-placebo. Both hypotheses received statistically significant support.