12.3 What is Adult Intelligence?

Adult Intelligence The achievements of Jane Goodall (left) and Ellen Johnson-Sirleaf (right) are indicators of the success that is possible later in life.

AFP/GETTY IMAGES/JENS SCHLUETER
SALVATORE DI NOLFI/EPA/CORBIS

You just read that both education and intelligence, measured by IQ tests, might explain why high-SES adults are healthier than those of low SES. But is there such a thing as “intelligence”? You read in Chapter 7 that intelligence in childhood correlates with school achievement, itself controversial. However, what about intellectual development over the years of adulthood?

One leading theoretician, Charles Spearman (1927), proposed a single entity that he called general intelligence (g). Although g cannot be measured directly, it can be inferred from various abilities, such as vocabulary, memory, and reasoning. Most experts who agree with Spearman contend that children gain in ability as they mature, and thus scores on intelligence tests take a child’s age into account. Once a person reaches adulthood, an IQ score indicates whether that adult is a genius, average, or below average, no matter what the person’s age. The same IQ test is taken at age 18 or 88.

The belief that g exists still influences thinking and testing on intelligence. Many neuroscientists seek genetic underpinnings for the intellectual differences among adults. However, efforts to find specific genes or abilities that comprise g have not succeeded (Deary et al., 2010; Haier et al., 2009). Some researchers believe g does not exist.

Research on Age and Intelligence

Research on intelligence over the years of adulthood has reached conflicting conclusions (Hertzog, 2011). Cross-sectional studies find that intellectual ability peaks in adolescence and then gradually declines. Typical 50-year-olds score lower on IQ tests than typical 25-year-olds do, and 50-year-olds score higher than typical 75-year-olds do. However, when longitudinal research is conducted, testing the same people again and again as they age, scores improve—at least until late adulthood. Those 50-year-olds score higher than they did at age 25. How could this be?

The Flynn EffectThe most plausible hypothesis for the divergence between the conclusions of cross-sectional and longitudinal research begins with a fact: For most of the past century, each generation was healthier and better educated than the previous one.

In many nations, the typical 75-year-old had never attended college or university, but now a typical 25-year-old has some college or university education. Furthermore, 25-year-olds have had better childhood health (vaccines, nutrition) and more information (via television and computers) available to them. That affects intelligence; younger cohorts would therefore have higher IQ scores on cross-sectional research.

The same factors explain the results of longitudinal research. Contemporary 75-year-olds have experienced those advantages as they aged, being better informed about the world than they were as children. For that reason, longitudinal research would find them scoring higher than they did 50 years ago. Powerful evidence supporting this explanation comes from test scores in many nations (Dickinson & Hiscock, 2010). In every country where data allow a valid comparison, more recent cohorts outscore previous generations tested at the same age. This is called the Flynn effect.

As a result it is unfair—and scientifically invalid—to compare IQ scores of a cross section of adults of various ages. Older adults will score lower, but that does not mean they have lost intellectual power; quite the opposite is the case. (This may not be true for the oldest adults, however; more on that in Chapter 14).

Cross-Sequential ResearchScientists now realize that neither cross-sectional nor longitudinal research is completely accurate to ascertain age changes, since historical conditions change as well (Hertzog, 2011). The best way to understand the effects of time without the confounding complications of contextual changes is to combine the two. One scholar famously pioneered this combination.

As an undergraduate in the middle of the twentieth century, K. Warner Schaie began to study adult intelligence. For his doctoral dissertation, he tested 500 adults, aged 20 to 50, on five standard primary mental abilities thought to be the foundation of intelligence: (1) verbal meaning (vocabulary), (2) spatial orientation, (3) inductive reasoning, (4) number ability, and (5) word fluency (rapid verbal associations). Schaie’s initial cross-sectional results showed a gradual, age-related decline in these five abilities, as others had found before him. He had read that longitudinal research found an increase in IQ, so he planned to retest his population seven years later.

He then had a brilliant idea: He would not only retest his initial participants, he would also test a new young group who were the same age as his earlier sample had been. By comparing the scores of the retested individuals with their own earlier scores and with the scores of a new group who were the same age as his first group had been, he hoped to learn more about age and intelligence. His results surprised the experts; he discovered cohort effects that few people had imagined earlier.

For example, each successive cohort scored higher in verbal memory and inductive reasoning, but scored lower in number ability than adults who had been tested seven years earlier at the same age. That led to the hypothesis that classroom teaching affected ability: The curriculum in many U.S. schools had shifted by mid-century to emphasize reading, writing, and self-expression, not math.

Schaie found that one correlate of higher ability was intellectual complexity at work and at home, both of which tended to peak in middle age, from ages 39 to 53. Because of complexity, women of earlier cohorts, who often stayed home or had less challenging jobs, lost IQ in mid-life, but this did not occur for contemporary women.

Schaie conducted the first massive cross-sequential research. Cross-age comparisons allowed analysis of potential influences, including retesting, cohort differences, experience, education, and gender. Ten times over more than five decades, Schaie and his colleagues have tested a new group and retested his earlier participants (Schaie, 2005). The results of this project, known as the Seattle Longitudinal Study, confirmed and extended what others had found: People improve in most mental abilities during adulthood. As Figure 12.4 shows, each particular ability at each age and for each gender has a distinct pattern. All abilities gradually improve and then eventually decline. Men are initially better with numbers and women with words, and that gap narrows with age.

FIGURE 12.4 Age Differences in Intellectual Abilities Cross-sectional data on intellectual abilities at various ages show much steeper declines. Longitudinal research, in contrast, shows more notable rises. Because Schaie’s research is cross-sequential, the trajectories it depicts are more revealing: None of the average scores for the five abilities at any age is above 55 or below 35. Because the methodology takes into account the cohort and historical effects, the age-related differences from ages 25 to 60 are very small.

Source: Schaie, 2005.

Many other researchers have reported similar results (Alwin, 2009). For example, Paul Baltes (2003) tested hundreds of older Germans in Berlin and found that only at age 80 did every cognitive ability show age-related declines. As noted earlier in this chapter, for some people aging impairs the brain, reducing cognition. But more often adult IQ increases, or at least stays the same.

Components of Intelligence: Many and Varied

Developmentalists are now looking closely at patterns of cognitive gains and losses over the adult years. These patterns vary markedly; intelligence often rises and falls within the same person, as “vast domains of cognitive performance…may not follow a common, age-linked trajectory of decline” (Dannefer & Patterson, 2008).

As you read in Chapter 7, many psychologists envision multiple intellectual abilities (Roberts & Lipnevich, 2012). One influential proposal—Gardner’s theory of nine multiple intelligences, with its many implications for childhood education—was explained in Chapter 7. We now consider two other proposals in detail.

Fluid and Crystallized IntelligenceIn the 1960s, leading personality researcher Raymond Cattell teamed up with a graduate student, John Horn, to study intelligence tests. They concluded that adult intelligence is best understood if various measures are grouped into two categories: fluid and crystallized (Horn & Cattell, 1967).

Think Before Acting Both these adults need to combine fluid and crystallized intelligence, insight and intuition, logic and experience. One (left) is a surgeon, studying X-rays before picking up her scalpel. The other (right) is the executive director of a community organization in Mississauga, Ontario, and a part-time doctoral student at the University of Guelph, reading about a new resource for immigrant parents of young children.

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PRIYANKA SEKHAR

As its name implies, fluid intelligence is like water, flowing to its own level no matter where it happens to be. Fluid intelligence is quick and flexible, enabling people to learn anything, even things that are unfamiliar and unconnected to what they already know. Curiosity, learning for the joy of it, and the thrill of discovering something new are marks of fluid intelligence (Silvia & Sanders, 2010).

People high in fluid abilities can draw inferences, understand relations between concepts, and quickly process new ideas and facts. They are fast and creative with words and numbers and enjoy intellectual puzzles. The kind of question that tests fluid intelligence among Western adults might be like these:

Puzzles are often used to measure fluid intelligence, with speedy solutions earning bonus points (as on many IQ tests). Efficient working memory—with immediate recall of nonsense words, of numbers, of a sentence just read—is a crucial aspect of fluid intelligence.

A study of adults aged 34 to 83 found that stresses and stressors did not vary by age, but did vary by fluid intelligence. People high in fluid intelligence were more often exposed to stress but were less likely to suffer from it: They used their intellect to turn potential stressors into positive experiences (Stawski et al., 2010). Fluid intelligence is associated with openness to new experiences and overall brain health (Batterham et al., 2009; Silvia & Sanders, 2010), which may contribute to an ability to detoxify stress. That may be one reason why high fluid intelligence in emerging adulthood leads to longer life and higher IQ later in adulthood.

By contrast, the accumulation of facts, information, and knowledge as a result of education and experience is called crystallized intelligence. Size of vocabulary, knowledge of chemical formulas, and memory for dates all indicate crystallized intelligence. Tests to measure this intelligence might include questions like these:

Although questions that test for crystallized intelligence seem to measure education more than aptitude, these two are connected, especially in adulthood. Intelligent adults read widely, think deeply, and remember what they learn: Crystallized intelligence reflects fluid intelligence. Consequently, many researchers consider years of education a rough indication of IQ.

Age complicates the calculation of adult IQ. Scores on items measuring fluid intelligence decrease with age since everything in the brain as well as the body slows down. However, if a person continues to read and think, scores on items measuring crystallized intelligence increase. These two clusters, changing in opposite directions, make a person’s IQ score (composed of diverse subtests) fairly steady from ages 30 to 70, even though particular abilities change.

Barring pathology, the brain slowdown is rarely apparent until massive declines in fluid intelligence begin to affect crystallized intelligence, perhaps at age 70 or so. It may be foolish to try to measure g, a single omnibus intelligence, because both fluid and crystallized intelligence need to be measured separately.

When thinking about age changes in fluid and crystallized intelligence, note the connection between speed and IQ. Many items that test fluid intelligence are timed, with extra points for quick answers. In a culture that values youth, abilities that favour the young (e.g., fast reaction time, capacious short-term memory) are central to success on psychometric intelligence tests, whereas the strengths of older adults (e.g., emotional regulation and the upholding of traditional values) are not.

Thus, fluid intelligence is valued in a youth-oriented culture more than crystallized intelligence. A word often used to describe a highly intelligent person is quick, whereas a less intelligent person is called slow—exactly what happens with age. Perhaps the assumptions that led to the creation of IQ tests are faulty when applied to adults.

Three Forms of Intelligence: Sternberg Robert Sternberg (1988, 2003) agrees that the notion of a single intelligence score is misleading. As first mentioned in Chapter 7, Sternberg proposed three fundamental forms of intelligence: analytic, creative, and practical. Each can be tested.

Analytic intelligence includes all the mental processes that foster academic proficiency. It draws on abstract planning, strategy selection, focused attention, memory, and information processing, as well as on verbal and logical skills. Strengths in those areas are particularly valuable for younger adults in higher education and job training. Multiple-choice tests and brief essays that call forth remembered information, with one and only one right answer, indicate analytic intelligence.

Creative intelligence involves the capacity to be intellectually flexible and innovative. Creative thinking is divergent rather than convergent, valuing unexpected, imaginative, and unusual thoughts rather than standard and conventional ones. Sternberg developed tests of creative intelligence that include writing a short story titled “The Octopus’s Sneakers” or planning an advertising campaign for a new doorknob. High scores are earned by those with many unusual ideas.

Practical intelligence involves the capacity to adapt to the demands of a given situation. This includes an accurate grasp of the expectations and needs of the people involved and an awareness of the particular skills that are called for, along with the ability to use these insights effectively. If employers want to assess practical intelligence, they might test workers with a case study or see how they function on the job. Practical intelligence is sometimes called tacit intelligence because it is not obvious on tests. Instead it comes from “the school of hard knocks” and is sometimes called “street smarts” rather than “book smarts.”

Practical intelligence is needed in adulthood. It allows a person to manage the conflicting personalities in a family or to convince members of an organization (e.g., a business, a social group, or a school) to do something. Ideally, practical intelligence gradually builds over the years, as people learn from experience. Flexibility is also needed, as you will soon see in the discussion of expertise (K. Sloan, 2009).

Without practical intelligence, a solution found by analytic intelligence is doomed to fail because people resist academic brilliance as unrealistic and elite. Similarly, a stunningly creative idea may be rejected as ridiculous without practical intelligence.

Smart Farmer This creative field trip is to a wheat field, where children study grains that will become bread. Farmers like this one use every kind of intelligence. To succeed they need to decide what crops and seed varieties to plant, to anticipate market prices, and to analyze soil, fertilizer, pests, and so on.

PETER BECK/CORBIS

Sternberg believes that each of these three forms of intelligence is useful; adults ideally deploy the strengths and guard against the limitations of each. Choosing which type of intelligence to use takes wisdom, which Sternberg has added as a fourth ingredient of successful intelligence. He writes:

Think about these intelligences cross-culturally. Each type might be more appreciated in some situations than in others. For example, analytic individuals would do well in college or university but might be seen as arrogant and be criticized for being the “elite” when in a different environment. Creative individuals are critical of tradition and would be tolerated only in some political environments (Sternberg, 2006b). Practical intelligence might be particularly needed when traditional customs and practices no longer seem useful.

The fact that those who do well in college or university might not adapt well to life outside of school raises the question—what do adults need to do in order to succeed? In a knowledge economy, analytic intelligence may be crucial…or may not be. Opposing perspectives on this are illustrated by asking, “What makes a good parent?”

Same Situation, Far Apart: Men at Work The bean merchant in Nairobi, Kenya (left), and the construction supervisor in Beijing, China (right), have much in common: They are high in practical intelligence and they love their jobs. Context is crucial to their success since, if they traded places, each would be lost at first. However, practical intelligence could save the day—a few months of intensive instruction might enable each to master his new role.

FREDRICK ONYANGO
BLUE JEAN IMAGES/GETTY IMAGES

OPPOSING PERSPECTIVES

What Makes a Good Parent?

Tests of good infant care have been developed, based primarily on analytic, not practical, child-rearing (e.g., McCall et al., 2010). One of the most common scales is the Knowledge of Infant Development Inventory (KIDI) (MacPhee, 1981). KIDI measures how much caregivers know about infant senses, motor skills, and communication—such as at what age an infant is expected to sit up or whether parents should talk to pre-verbal babies.

Such knowledge seems helpful. For example, mothers and fathers who score higher on the KIDI are less depressed and more likely to provide responsive baby care (Howard, 2010; Zolotor et al., 2008). Many researchers believe that knowledge of infant development causes (not merely correlates with) good care.

Should we worry when mothers do not know about their babies’ growth? Perhaps. For instance, in one study only 29 percent of immigrant mothers knew that 2-month-olds can distinguish one speech sound from another, an item on the KIDI. The researchers suggest that those mothers are less able to advance their infants’ language and social skills, hindering future development (Bornstein & Cote, 2007).

The opposing perspective suggests that knowledge of infant development does not matter in caregiving. A study supporting this view found that an immigrant child’s later cognitive development was best predicted not by KIDI scores or other measures of parenting, but by parents’ SES and language use. In this longitudinal study, the mothers’ KIDI scores did not predict later school success for Asian-American or Latino children, but it did for European-American children (Han et al., 2012).

Keep Him Close Mothers everywhere keep their toddlers nearby, but it is particularly important in an environment where poisonous spiders and plants thrive. This Ache mother is required to use analytic intelligence (e.g., to assess danger), as well as creative and practical intelligence (e.g., to keep her child safe).

TERRY WHITTAKER/ALAMY

In another study, researchers provided supportive, encouraging visitors to low-income, unmarried mothers—many of whom did not plan or want their babies. Compared with a control group with no visits, and even compared with mothers in the intervention group who had relatively few home visits, mothers who were visited 30 or more times became better infant caregivers. However, both before and after many visits, the KIDI scores of the mothers were low. The authors of the study wrote:

A significant impact of this intervention was its effect on the mothers’ ability to create home environments more suitable for the needs of their infants…despite lack of measurable change in mothers’ knowledge of infant development.

[Katz et al, 2011, p. S81]

In other words, advances in practical skills, not analytic ones, made a difference.

Knowledge may not be the only way to improve parenting. Instead, warmth and patience, responsiveness (without expecting an infant to reciprocate), mental health, or social support networks may be more critical than knowledge.

Part of the underlying reason why tests of knowledge do not always predict good parenting is that cultures vary in what they believe about infant development. For example, an anthropologist studied the Ache in Paraguay. They were respectful and deferential to her on repeated visits, until she and her husband

arrived at their study site in the forest of Paraguay with their infant daughter in tow. The Ache greeted her in a whole new way. They took her aside and in friendly and intimate but no-nonsense terms told her all the things she was doing wrong as a mother…. “This older woman sat with me and told me I must sleep with my daughter. They were horrified that I brought a basket with me for her to sleep in.” Here was a group of forest hunter-gatherers, people living in what Westerners would call basic conditions, giving instructions to a highly educated woman from a technologically sophisticated culture.

[Small, 1998]

How important to quality care is accurate knowledge of child development? The way knowledge is interpreted and used by parents is complicated by various factors such as culture and SES, as we have just read. In the end, the most important aspect of good parenting may not be information, and the sign of an intelligent adult may be something other than analytic intelligence. What we do know about child care is that parents need to be continually responsive and sensitive to their children’s development, both of which require creative and practical intelligence.

*fluid intelligence answers are 6 and F; other answers are possible.

^§The crystallized intelligence answers might be: someone who dislikes people; a fisherman who caught whales or swordfish in the past; Ceylon.