Aging and Speed of Behavior: CNS Arousal and Reaction Time Distribution Analyses

Abstract

This research sought to determine the impact of arousal/activation, sex/gender, stimulus quality, practice, and task type on age-related slowing, as measured by reaction time, with analysis of RT distribution characteristics. Forty-four male and female subjects participated in the experiment: 28 young and 16 elderly. Subjects performed four-choice visual reaction tasks while seated and standing (postural stimulation of the central nervous system), with intersession practice and a complete replication of the study on a second day. Visual stimuli were presented as variable choice reaction time (VCRT) and serial choice reaction time (SCRT) tasks, i.e., in intact and degraded forms at varying response stimulus intervals (RSIs) and at a fixed response stimulus interval (RSI = 0), respectively. Data were analyzed by central tendency as well as variance, skewness, and unusually fast or slow responses. In addition to expected age-related slowing, results showed increased variance in elderly RT distributions, an overall shift in elderly versus young RT distributions, and a task dependent change in the shape of elderly RT distributions. For the fixed RSI task, which required sustained continuous performance; it was concluded that elderly subjects had a more difficult time than young subjects transitioning from the previous response to the current stimulus. For the variable RSI task, it was concluded that elderly subjects were more likely than young subjects to be caught “off guard”, unprepared to respond. Standing (increased arousal) decreased the likelihood that elderly subjects would be unprepared to respond thereby reducing speed difference by age. This investigation suggests that several mechanisms interact to cause not only a shift in elderly versus young RT distributions, but also changes in skewness and/or unusually slow responses.