EFFECTS OF CAFFEINE AND CAFFEINE-ASSOCIATED STIMULI ON THE HUMAN STARTLE EYEBLINK REFLEX

An experiment was performed (n = 19) that investigated the effect of c affeine and expectancy of caffeine on the eyeblink component of the st artle reflex. Nineteen habitual caffeine users received caffeinated co ffee, caffeinated juice, decaffeinated coffee, or decaffeinated juice in four sessions spaced 1 week apart. Twenty-five to 30 min after inge stion of the liquid, 30 acoustic startle stimuli were presented. The r esults showed that caffeine increased startle eyeblink amplitude. Star tle reflex onset latency was significantly longer in the decaffeinated coffee condition than in the other three conditions. This may have be en due to the activation of a compensatory slowing of the reflex by th e anticipation of caffeine, a slowing that was then overridden by caff eine speeding the response. (C) 1998 Elsevier Science Inc.