Caffeine consumption and target scanning performance.

Abstract

Twenty-five minutes after ingesting one of three possible dosages (placebo, 200 mg, or 400 mg) of caffeine, 48 subjects individually participated in two short-term visual target scanning tasks (subject-paced and experimenter-paced). Assignment of subjects to treatment groups was made on the basis of a priori coffee consumption rates. Subjects who reported that they normally consumed less than three cups of coffee per week (average) were assigned to the low usage rate group (LR), while those who reported average consumption rates of three cups or more per week were assigned to the high usage rate group (HR). Latencies were obtained for the subject-paced measure by allowing subjects to scan ten 10 × 10 matrices until the target was found. Correct detection percentages were taken for the experimenter-paced task by allowing subjects to scan ten 10 × 10 matrices for 5 s and report whether or not a pre-announced target number was contained in the matrix. Significant differences in latencies were obtained between LR and HR only with 400 mg caffeine dosages. LR exhibited significantly higher latencies as a function of these dosages than did HR. No reliable differences occurred between LR and HR for correct detection percentages.