Intelligence in Older Adulthood Psychologists describe two basic types of intelligence: Fluid intelligence and crystallized intelligence. The idea that intelligence is static -- that it is a fundamental personal attribute that is immutable long ago fell out of disfavor with scientists. Current research suggests that fluid intelligence does begin to lessen in the over the life span, with adolescence being the watershed years. Crystallized intelligence, however, can continue to increase throughout the lifespan. The concepts of fluid and crystallized intelligence were proposed by Raymond Cattell, who later worked with John Horn to further develop the theory. What is now known as the Cattell-Horn theory of fluid and crystallized intelligence proposes that various abilities interact with a synergy that generates what is known as overall individual intelligence.

Fluid intelligence. The ability to problem-solve and reason abstractly independent of prior learning, experience, and education or training is considered to be fluid intelligence. Fluid intelligence occurs when there has been no practice, no instruction, no training, and no education that would establish a foundation for perceiving and understanding relationships in a problem-solving or abstract thinking exercise. A common example of fluid intelligence it the ability to solve puzzles, or the capacity to generate problem-solving strategies for scenarios for which no previous experience exists. Generally, fluid intelligence reaches its apex in adolescence and by about age 30 or 40, it begins to decline.

Crystallized intelligence. Our ability to learn from past experience in a way that builds a foundation of knowledge and skills from which we can draw, is called crystallized intelligence. The ability to understand what is read, to figure out new vocabulary, to understand patterns in relationships, and make predictions based on prior encounters with situations are all examples of crystallized intelligence. Crystallized intelligence increases as people age -- the accumulation of new knowledge, comprehension of new situations, and the understanding of newly encountered relationships contributes to a strengthened crystallized intelligence over most of the lifespan.

Seattle Longitudinal Study. Fluid and crystallized intelligence "constitute the...

Fluid and crystallized intelligence are complementary in that some learning tasks can be mastered mainly by exercising either fluid or crystallized intelligence" (Knox, 1977, p. 420).
Variables Impacting Lessening IQs in Older Adults. The significance of the Seattle Longitudinal Study is that researchers learned that intelligence is very plastic and much more responsive to environmental influence than previously believed. Further, intellectual change is multidirectional and individual-specific -- some abilities decline and some abilities rise -- and that there are dramatic differences in individuals in terms of change and stability. The study results demonstrated that by age 60, practically everyone shows some loss on one primary intellectual ability, but even by age 88, virtually no one shows a decline in all five primary intellectual abilities. The study has added to the literature with regard to understanding the mental abilities of the elderly by clarifying attributes of the patterns in changes in intellectual functioning; the study confirmed the general theory that intelligence increases until the early 40s, then stability until the mid 50s or mid 60s, and then after age 60, seven-year losses are statistically significant. But the Seattle longitudinal Study also demonstrated that generalization could lead to conclusions that were completely off the mark, individual differences being so great.

Speed in intellectual function. Much of the loss in fluid intellectual quotient is due slower thinking speeds. However, differences were found in speed of thinking that were related to activity level (sedentary vs. active) and the presence or absence of brain-impacting illness.

Impact of illness on intellectual function. By middle age, most people have one chronic condition; by age 80, functional heath impairments are common. Totally healthy elderly men out-performed less-than ideally healthy men on 10 out of 11 subtests on an intelligence test similar to the WAIS. Older people with a wide range of chronic illnesses consistently scored lower on tests of intellectual capacity than did healthy age-mate adults. An extension of this theory is related to a phenomenon called terminal drop, in which people who…