Behavioral changes with age are as striking as changes in physical appearance. Both training and altered structures contribute to these psychological differences. Differences that occur throughout the life span are mainly studied by cross-sectional and longitudinal methods.
Age differences in intelligence have been extensively studied. Mental age (MA) as measured by standard intelligence tests increases with chronological age (CA), and because of the way age scales are constructed, the relation is linear. An average child shows an increase of 1 year in MA for each year of CA until about 15 to 18 years of age, when MAis assumed to level off. There is evidence, however, that the intellectual ability of some individuals may continue to increase at least until they are in their early 20s.
The question of the growth of MAwith age is complicated by two factors: (1) the difficulty level of items for young adults, and (2) the different composition of abilities tested at different age levels. If there are few difficult items at the upper end of the scale, older subjects cannot show improvement: The ceiling of the test is too low. If the same functions are not being tested at different age levels, what does it mean to say that MA increases with age?
The constancy of IQ across time has long been an age-related issue. In general, IQs of schoolchildren and adults have been found to be constant enough to allow satisfactory prediction over several years. And within limits, the older the subjects, the longer the test scores remain relatively constant (within 4 to 5 IQ points). At the opposite extreme, preschool IQs are very poor predictors of scores obtained later in life. It should be emphasized, however, that, even when test-retest correlations are high for a group, sizable systematic shifts in IQ can occur in particular individuals. Achange of 30 or more points in a mean of 12 years has been found in 9% of the cases studied by Honzik, Macfarlane, and Allen.
Interestingly, there is often a large drop in IQ a few years before death, regardless of when death occurs. Such a drop in IQ can even be used to predict death.
The fact that recognition memory and recall show decided improvement in children, say, between ages 6 and 9 is probably related to an increase in mental age. The older children use implicit verbalization more—labeling, rehearsing, and comparing stimuli. Age seems to affect recall performance more than recognition, improving performance in children and hindering it in old age.
A fair number of generalizations can be made about behavior changes in later life.
1. Since behavior is in part a product of the central nervous system, the loss of brain cells with age is probably a relevant consideration. By the age of 80 or 90, 40% of cortical cells may be lost. Also, water content declines and fats increase in the brain over the life span.
2. Older people definitely have more health problems than the young, which inevitably modifies their behavior.
3. Visual acuity and accommodation decline because of the increase in opacity and loss of elasticity of the lens of the eye in middle age. Changes in the retina later in life also impair color vision and increase sensitivity to glare.
4. Similarly, in audition, perception of higher frequencies disappears in the middle years, and after age 65 many adults require (although they do not necessarily use) hearing aids. Stress due to hearing loss can produce depression and other emotional disorders.
5. There is also declining sensitivity in taste, smell, and pain in the later years.
6. Older people seem to take longer to learn verbal material than do the young. However, when the learning of older people is self-paced and meaningful, they perform well. They also improve in learning and long-term memory when instructed to use mediating or mnemonic devices.
7. Older people's deficit in long-term memory seems to be mainly one of retrieval; short-term memory is impaired only when the task requires divided attention (e.g., dichotic listening). Span remains essentially intact until very advanced years.
8. Individual variability in all intellectual tasks increases over the life span, but this does not pose an educational problem until around 70 years of age or later.
9. With increasing age the central nervous system slows down. This change appears to account for the gradual decrease in speed of responding across the life span for a wide range of tasks, including reaction time, sorting objects, copying, canceling, and other similar processing functions.
10. Although there are few studies on problem solving and creativity as functions of aging, some hypotheses have emerged:
• Older subjects tend to ask uninformative questions, to be disrupted by irrelevant and redundant information, and to treat both positive and negative instances of a concept as positive. Failure to profit from negative information can make a person seem rigid.
• If memory load is kept low and older people are given strategy hints and the like, age-related deficits in problem solving can be substantially reduced (Sanders et al., 1975).
• Although Lehman (1953) concluded that most creative achievements occur early in a scientist's or artist's career, considerable evidence indicates that some of the most valuable contributions come late in life. For example, Claude Monet began his famed "Water Lily" series at age 73; Benjamin Franklin invented the bifocal lens at 78; Sophocles wrote Oedipus Rex at 75; and George Bernard Shaw wrote his first play at 48. When the quality of works by Bach and Beethoven is assessed by the number of times a piece has been recorded, the latest works excel.
11. As one grows older, interests change; for example, the participant in sports becomes a spectator, and the incidence of crime declines steadily.
12. Finally, well-conducted sequential studies suggest that a person's personality is characterized more by continuity than by change. Cohort differences appear to be more prevalent than age changes.
See also: Alzheimer's Disease; Human Development; Lifespan Development; Longitudinal Studies
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