Effects of caffeine on perceptual judgment.

The present study examined the effects of caffeine on the estimation of felt width of blocks employing haptic presentation. Following a between-subject design, 160 male postgraduate students classified as high or low impulsives received either placebo or one of four doses of caffeine citrate (1, 2, 3 and 4 mg/kg body weight). A double-blind procedure was adopted for drug administration. Caffeine produced differential effects on the performance of high and low impulsives, facilitated performance (decreased error in perceptual judgment) in high impulsives but had no influence on the performance of low impulsives. The dose-response trends also followed different patterns in the two groups of subjects.