Simple reaction time as a function of time uncertainty.

An earlier study (3) showed that simple reaction time (RT) varies 'with S's uncertainty about time of stimulus occurrence. This time uncertainty is a function of both the mean duration of the time (foreperiod) between a warning signal and the stimulus and the variability within the series of foreperiods. Foreperiod variability adds uncertainty directly and mean foreperiod is important since S's ability to predict time of stimulus occurrence is very much a function of the length of time he must predict. In the previous report the two sources of time uncertainty were considered separately because no single measure was available. The present experiment illustrates with new data, a method by which all of S's time uncertainty can be expressed as a single number and reaction time plotted as a single-valued function of time uncertainty. In addition, time uncertainty is expressed in terms of the information measure. In order to estimate the amount of time uncertainty due to S's imperfect time-keeping ability, it is necessary to run time-interval prediction tests with intervals equal to the mean foreperiods of the reaction time tests. The variance of the distribution of each S's times of response in the time prediction test is taken as a measure of his "subjective" time uncertainty