INTELLECTUAL FUNCTIONING: THE NATURE AND PATTERN OF CHANGE WITH AGING.

Abstract

We know very little about the intellectual functioning of the elderly. In the past, IQ normative data has been gathered using simple cross-sectional designs but these designs confound aging and generational effects, leaving interpretation unclear. Longitudinal studies have also been done, but the results can't be generalized because practice and sample bias effects are confounded with aging effects. In addition, nearly all the research to date either uses a very restricted age range or uses a limited number of measures, many of which have not been adequately validated with respect to predicting functional ability. The present set of studies used tests from the Halstead-Reitan Neuropsychological Battery for Adults. The tests were organized into measures most sensitive to retention of prior learning, sensory input, motor output, language processes, visuo-spatial processes, abstract reasoning, and a combined measure of central processing. These measures allowed accurate characterization of a broad range of brain-related functions both across groups and within single individuals. This research was divided into two related studies. The first study measured the performance of 125 neurologically normal subjects divided into 5 equal sized age groups (20-29, 30-39, 40-49, 50-59, 60-70). The second study used 3 groups (a young neurologically normal group, an older neurologically normal group, and a young brain-damaged group). Results of the present investigation showed that: (1) Retention of prior learning did not change across age groups. (2) Sensory input functions deteriorated with age, but the actual amount of change was modest and limited to measures using complex stimuli. (3) Simple motor output ability showed no significant change with age, but complex motor performance did deteriorate substantially. (4) Language processing ability decreased significantly with age, but the actual amount of change was small. (5) Complex visuo-spatial ability deteriorated substantially with age, and a particular decrement took place for those in their 60s. (6) Marked deterioration of abstraction ability took place with increasing age, and again those in their 60s showed a particularly large decrement of performance.