Aging and slowing of behavior: consequences for cognition and survival.

It has been over a hundred years since Francis Galton observed that older persons responded more slowly than the young. Since then, slowness of behavior with age has become the most robust phenomenon seen in research on aging. Interest in the slowness of behavior with age, in fact, has been growing in scientific significance because of the relation of speed to cognitive functions, on the one hand, and to physical fitness and electrophysiological measurements on the other. In addition, speed of behavior may be viewed as a reliable marker of aging. This broader context gives rise to the question of how speed of behavior is related to the hierarchical organization of the functions of the central nervous system, a topic neglected by both general and developmental psychologists. Speed of behavior apparently limits certain intellectual components such as fluid intelligence and the important precognitive capacity of attention. Although there may be several speed factors, at least one broad one has pervasive influence on abilities. It appears that the relations among age, speed, and cognitive abilities are not similar to those of other domains of general psychology, and for that reason changes in speed and its role in behavior cannot easily be captured in terms of familiar metaphors of psychology. We must seek new metaphors that can characterize the complexity of aging as a process of transformation and also embrace the apparent contradictions seen in simultaneous increases and decreases in behavioral capacities with age. New research should be considered to take advantage of the robustness of the observed slowness of behavior with age and its widespread correlation with other behavioral and physiological functions. As one of the most reliable psychological markers of aging, it may be used in longitudinal studies to gain further insight into the organization of aging. One of the topics speed of behavior may contribute to is the relation of an energetic concept of aging involving metabolism and capacity for work to an informational or control concept--for example, gaining some insight into the relative contributions of "software" and "hardware" factors in human aging. It appears that in mammals a relatively large nervous system is related to a longer life span. Perhaps for humans, the eventual limiting factor on longevity is the integrity of the nervous system with its fixed long-lived neurons. Future studies of aging may well place greater emphasis on the part the central nervous system plays in aging owing to its role as the integrator of bodily functions.(ABSTRACT TRUNCATED AT 400 WORDS)