Caffeine and visuo-spatial attention.

The effects of two doses of caffeine (1.5 and 3 mg/kg) on various aspects of visual selective attention were investigated in 24 healthy human subjects. Specific task conditions were compared to provide measures of selectivity for a location in the visual field, of distractibility, of selectivity among response alternatives, and of strategic influences. In two out of three tasks, caffeine speeded responses significantly. However, these effects did not differ across conditions within-task, so there was no indication that they were to due to (a) specific effect(s) on one or more of the attentional sub-functions. The results suggest that the beneficial effects of caffeine in low-load conditions cannot be attributed to reduced distractibility or increased suppression of task-irrelevant response tendencies.