Effects of preparatory intervals and stimulus intensity on reaction times of normal and retarded individuals.

Abstract

A simple reaction time (RT) task was employed in which the relationships among intelligence, preparatory intervals (Pis), and intensity were examined. Both signal intensity and Pis were found to interact with level of intelligence. However, the context of stimulus and temporal presentations affected normal and retarded individuals similarly. An additional interaction was obtained involving signal intensity and Pis. Intensity was found to have a more pronounced effect under short PI conditions. These findings are discussed in relation to contextual effects. The major purpose of the present investigation was to compare the reaction times (RTs) of normal and mentally retarded individuals. The emphasis in the present research was on interactions between the organismic variable of intelligence and certain experimental variables. In this context, the relationships between intelligence and preparatory intervals (Pis), and intelligence and reaction-signal intensity were examined. Two previous comparative investigations have been conducted on auditory stimulus intensity with normal and retarded Ss (Baumeister, Hawkins, & Kellas, 1965a, 1965b). In one study, the range of intensity values was near threshold, whereas in the second the values sampled were well above threshold. Only in the latter instance was an interaction demonstrated between intelligence and intensity; and, in this case, the interaction obtained only for certain orders of stimulus presentation. In both experiments, the stimulus values were constant within blocks of trials. Grice and Hunter (1964) and Grice (1966) have demonstrated that the function describing stimulus-intensity effects on RT depends, in part, on the experimental design. The slope of the intensity function was steeper for within-Ss random stimuli presentation than when intensity values were pre