Simple reaction time as a function of foreperiod duration was determined for 6 foreperiod distributions characterized as leptokurtic, bimodal, or rectangular. S's inability to maintain a peak level of readiness geared to the most frequently occurring foreperiod suggested a "ballistic" type of preparation which was relatively independent of the conditional probability of occurrence of the stimulus during the foreperiod. (PsycINFO Database Record (c) 2006 APA, all rights reserved)