One of the weaknesses of studies of the aged has been the bias in selection of patients. Many of the reported observations have been made in cohorts of individuals residing in nursing homes. Studies of functionally intact old people of comparable age and living independently, such as those of Kokmen (1977) and of Benassi and their colleagues, reveal fewer deficits, consisting mainly of forgetfulness of names, smallness of pupils, restriction of convergence and upward conjugate gaze, diminished Achilles reflexes and vibratory sense in the feet, stooped posture, and impairments of balance, agility, and gait (as mentioned earlier and in the following text).
Effects of Aging on Memory and Other Cognitive Functions
Probably the most detailed information as to the effects of age on the nervous system comes from the measurement of cognitive functions. In the course of standardization of the original Wechsler-Bellevue Intelligence Scale (1955), cross-sectional studies of large samples of the population indicated that there was a steady decline in cognitive function starting at 30 years of age and progressing into old age. Apparently all forms of cognitive function partake of this decline—although in general certain elements of the verbal scale (vocabulary, fund of information, and comprehension) withstand the effects of aging better than those of the performance scale (block design, reversal of digits, picture arrangement, object assembly, and the digit symbol task).
However, the concept of a linear regression of cognitive function with aging has had to be modified in the light of subsequent longitudinal studies. If the same individual is examined over a period of many years, there is virtually no decline in performance, as measured by tests of verbal function, until about 60 years of age. Beyond this age, verbal intelligence does decline, but very slowly—by an average of less than 5 percent through the seventh decade and by less than 10 percent through the eighth decade (Schaie and Hertzog). Also, in a series of 460 community-dwelling individuals (55 to 95 years of age) studied by Smith and coworkers (1992), there was no significant decline with age in verbal memory and in registration–attention; similar results were found by Petersen and colleagues in 161 normal, community-dwelling individuals 62 to 100 years of age. The most definite effects of age were in learning and memory and in problem solving—cognitive impairments probably attributable to a progressive reduction in the speed of processing information. The latter may be reflected in the slowing of event-related evoked potentials and by a number of special psychologic tests (see
Verhaeghen et al).
As regards these cognitive functions, the ability to memorize, acquire, and retain new information, recall of names, and avoidance of distraction once set on a course of action, diminishes with advancing age, particularly in those older than 70 years of age. Moreover, memory function may be disturbed in this way despite the relative retention of other intellectual abilities. Characteristically, there is difficulty with recall of a name or the specific date of an experience (“episodic” memory) despite a preservation of memory for the experience itself or for the many features of a person whose name is momentarily elusive (“tip-of-the-tongue syndrome”). Also characteristic is an inconsistent retrieval of the lost name or information at a later date. It has been found, however, that if older persons are allowed to learn new material very well, until no errors are made, they forget this information at a rate similar to that of younger individuals.