Cognition & Aging

Changes in cognition do not cease when we reach adulthood. As we get older, we continue to learn more things, but human cognitive ability does not uni- formly increase with added years, as we might expect if intelligence were only a matter of what one knows. Data compiled by Salthouse (1992) on two components of the Wechsler Adult Intelligence Scale-Revised (WAIS-R). One component deals with verbal intelligence, which includes elements such as vocabu- lary and language comprehension. As you can see, this component maintains itself quite constantly through the years. In con- trast, the performance component, which includes abilities such as reasoning and problem solving, decreases dramatically.
The importance of these declines in basic measures of cognitive ability can be easily exaggerated. Such tests are typi- cally given rapidly, and older adults do better on slower tests. Additionally, such
tests tend to be like school tests, and young adults have had more recent ex- perience with such tests. When it comes to relevant job-related behavior, older adults often do better than younger adults (e.g., Perlmutter, Kaplan, & Nyquist, 1990), owing both to their greater accumulation of knowledge and to their more mature approach to job demands. There is also evidence that previous generations did not do as well on tests even when they were young. This is the so-called “Flynn effect”—IQ scores appear to have risen about 3 points per decade over the previous century (Flynn, 2007). The comparisons in Figure 14.12 are not only of people of different ages but also of people who grew up in different periods. Some of the apparent decline in the figure might be due to differences among generations (education, nutrition, etc.) and not age-related factors.
Although non–age-related factors may explain some of the decline, there are substantial age-related declines in brain function. Brain cells gradually die, and some areas are particularly suscepti- ble to cell death. The hippocampus, which is particularly important to mem- ory loses about 5% of its cells every decade (Selkoe, 1992). Other cells, though they might not die, have been observed to shrink and at- rophy. On the other hand, there is some evidence for compensatory growth: Cells remaining in the hippocampus will grow to compensate for the age-re- lated deaths of their neighbors. There is also evidence for the birth of new neurons, particularly in the region of the hippocampus (E. Gould & Gross,
2002). Moreover, the number of new neurons seems to be very much related to the richness of a person’s experience. Although these new neurons are few in number compared with the number lost, they may be very valuable because new neurons are more plastic and may be critical to encoding new experiences.
Although there are age-related neural losses, they may be relatively mi- nor in most intellectually active adults. The real problem concerns the in- tellectual deficits associated with various brain-related disorders. The most common of these disorders is Alzheimer’s disease, which is associated with substantial impairment of brain function, particularly in the temporal region including the hippocampus. Many brain-related disorders progress slowly, and some of the reason for age-related deficits in tests such as that illustrated in Figure 14.12 may be that some of the older participants are in the early stages of such diseases. However, even when health factors are taken into account and when the perfor- mance of the same participants is tracked in longi- tudinal studies (so there is not a generational con- found), there is evidence for age-related intellectual decline, although it may not become significant until after age 60 (Schaie, 1996).
As we get older, a race is going on between growth in knowledge and loss of neural function. People in many professions (artists, scientists, philosophers) tend to produce their best work in their mid-thirties. Figure 14.13 shows some interesting data from Lehman (1953), who examined the works of 182 famous deceased philosophers who collectively wrote some 1,785 books. Figure 14.13 plots the probability that a book was considered that philosopher’s best book as a function of the age at which it was written. These philosophers remained prolific, publishing many books in their seventies. However, a book written in this decade is unlikely to be considered a philosopher’s best.1 Lehman reviewed data from a number of fields consistent with the hypothesis that the thirties tend to be the time of peak intellectual performance. People often maintain relatively high intellectual performance into their forties and fifties.
The evidence for an age-related correlation between brain function and cognition makes it clear that there is a contribution of biology to intelligence that knowledge cannot always overcome. Salthouse (1992) argued that, in in- formation-processing terms, people lose their ability to hold information in working memory with age. He contrasted participants of different ages on the reasoning problems. These problems differ in the number of premises that need to be combined to come to a particular solu- tion. As can be seen, people’s ability to solve these problems generally declines with the number of premises that need to be combined. However, this drop-off is much
steeper for older adults. Salthouse argued that older adults are slower than younger adults in information processing, which inhibits their ability to main- tain information in working memory. Even though these tests are not speeded, the amount of information that can be maintained in working memory is con- trolled by speed of processing.
■ Increased knowledge and maturity sometimes compensate for age- related declines in rates of information processing.