Affiliation:
1. Human Factors Department, ISSM and Laboratory of Attention and Motor Performance, Gerontology; University of Southern California, Los Angeles, CA 90089–0021
Abstract
Although age-related slowing has been documented in the literature for over four decades, our understanding of this phenomena is far from complete. Two pressing theoretical issues are (1) Does age affect the central nervous system (CNS) in a general or specific manner, and (2) In what way does the level of ambient CNS arousal change with age, and how do such changes affect speed of behavior. Thirty-two young and old male and female individuals served as subjects in this experiment. All subjects performed a tapping task, a simple RT task, and a variety of four choice visual RT tasks while lying, sitting, and standing. For the CRT task, either an intact or degraded stimulus was preceded by a response-stimulus interval (RSI) of either 0–sec, 1.5–sec, or 4–sec, while the mapping between the stimulus and response was either high or low. In addition to predicted main effects of age, task difficulty, degradation, compatibility, posture, and RSI, interactions occurred between age and task difficulty, age and stimulus quality, and age and S-R compatibility. Older subjects were disproportionately slower during the more difficult tasks, the degraded stimulus condition, and the low S-R compatibility condition. A three way interaction was also observed between posture, stimulus quality, and S-R compatibility such that posture effects were observed for each task except the most difficult task (degraded stimulus/low S-R compatibility condition). This posture by task loading effect depended on the age of the subject such that while the younger subjects benefitted from posture regardless of task, the old subjects actually showed a reversed posture effect (lying faster than standing) during the most difficult task. The results of this study support both behavioral correlates of the cycle time hypothesis proposed by Botwinick (1984): Namely that older subjects are slowed to a proportionately greater extent as tasks become more difficult, and that older subjects experience a generalized slowing across the various stages of information processing. Results also indicated that cognitive energetics function differently in the old than in the young. Specifically, during the performance of particularly difficult tasks when aroused, older subjects may suffer from overload (and a consequent performance decrement) not evident in younger subjects.