Periodicity within Reaction Time Distributions and Electromyograms

Abstract

This study investigates a periodic component in reaction time frequency distributions, that is, a tendency for responses to occur at regular, discrete intervals of time after stimulus presentation. Reaction time frequency distributions were plotted by a Computer of Average Transients and were obtained under stimulus conditions varying in sense modality stimulated (auditory and visual), and the intensity, colour, and duration of stimulation. The results indicated that there was periodicity in reaction time frequency distributions with a modal period of approximately 25 msec. It was found that the periodicty (a) was most evident when there was considerable variability in reaction time, and (b) tended to attenuate when a large number of reaction times were grouped. Other stimulus conditions appeared to have little effect on the periodicity. A significant correlation was found between the frequency of periodicity in the reaction time distributions and the electromyograms, both having a modal period of 25 msec. It was concluded that the periodicity in reaction time was the result of motor processes.