Factor analysis of choice reaction time in young and elderly subjects.

To increase the utility of reaction time in applied research, we investigated the dynamic characteristics of the button-press response in four two-choice reaction-time tasks. 11 dependent variables were derived from the performance of two groups of normal young and elderly subjects. Factor analysis yielded five factors: baseline, premotor, motor, force, and release. The factors derived from each single stimulus condition were differentially sensitive in separating the two groups. Young and elderly subjects were most consistently differentiated by a release factor in each of the four stimulus conditions. This factor was interpreted as being relatively free of cognitive components and presumed to incorporate high psychomotor organization. The least efficient in differentiation was the baseline factor; it separated the young and elderly subjects in only one stimulus condition. Four factors from the test with visual-verbal stimuli separated the two age groups statistically, while only two factors did so in the test with auditory-verbal stimuli. The differences between stimulus conditions were interpreted as evidence of microbehavioral adjustments in response-performance dynamics and varying strategies used in handling the task demands.