The purpose of this study was to determine the effects of uncertainties of time and occurrence on reaction time of mildly handicapped students. 33 students were randomly assigned to the following treatment groups: no catch-trials, 10% catch-trials, and 20% catch-trials. Randomly varied foreperiods of 1.5, 3.0, and 4.5 sec. were used in a reaction time task. The role of catch-trials varied over four days of testing. Reaction times following 3.0- and 4.5-sec. were significantly faster than measurements following a 1.5-sec. foreperiod.
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