CHAPTER 10

INTELLIGENCE

What Is Intelligence?

10-1 How do psychologists define intelligence, and what are the arguments for g?

Intelligence is a mental quality consisting of the potential to learn from experience, solve problems, and use knowledge to adapt to new situations. Charles Spearman proposed that we have one general intelligence (g) underlying all other specific mental abilities. He helped develop factor analysis, a statistical procedure that identifies clusters of related abilities. L. L. Thurstone disagreed and identified seven different clusters of mental abilities. Yet a tendency remained for high scorers in one cluster to score high in other clusters. Studies indicate that g scores are most predictive in novel situations and do not much correlate with skills in evolutionarily familiar situations.

10-2 How do Gardner’s and Sternberg’s theories of multiple intelligences differ, and what criticisms have they faced?

Savant syndrome seems to support Howard Gardner’s view that we have multiple intelligences. He proposed eight independent intelligences: linguistic, logical-mathematical, musical, spatial, bodily-kinesthetic, intrapersonal, interpersonal, and naturalist. (He has also proposed a ninth possible intelligence—existential intelligence—the ability to ponder deep questions about life.) Robert Sternberg’s triarchic theory proposes three intelligence areas that predict real-world skills: analytical (academic problem-solving), creative, and practical.

Critics note research that has confirmed a general intelligence factor. But highly successful people also tend to be conscientious, well-connected, and doggedly energetic.

10-3 What are the four components of emotional intelligence?

Emotional intelligence, which is an aspect of social intelligence, is the ability to perceive, understand, manage, and use emotions. Emotionally intelligent people achieve greater personal and professional success. Some critics question whether calling these abilities “intelligence” stretches that concept too far.

Assessing Intelligence

10-4 What is an intelligence test, and what is the difference between achievement and aptitude tests?

An intelligence test is a method for assessing an individual’s mental aptitudes and comparing them with others, using numerical scores. Aptitude tests measure the ability to learn, while achievement tests measure what we have already learned.

10-5 When and why were intelligence tests created, and how do today’s tests differ from early intelligence tests?

In the late 1800s, Francis Galton, who believed that genius was inherited, attempted but failed to construct a simple intelligence test. Alfred Binet, who tended toward an environmental explanation of intelligence differences, started the modern intelligence-testing movement in France in 1904 when he developed questions to help predict children’s future progress in the Paris school system. During the early twentieth century, Lewis Terman of Stanford University revised Binet’s work for use in the United States. Terman believed intelligence was inherited, and he thought his Stanford-Binet could help guide people toward appropriate opportunities. From such tests, William Stern contributed the concept of the IQ (intelligence quotient). During this period, intelligence tests were sometimes used to “document” scientists’ assumptions about the innate inferiority of certain ethnic and immigrant groups.

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The most widely used intelligence tests today are the Wechsler Adult Intelligence Scale (WAIS) and Wechsler’s tests for children. These tests differ from their predecessors in the way they offer an overall intelligence score as well as scores for various verbal and performance areas.

10-6 What is a normal curve, and what does it mean to say that a test has been standardized and is reliable and valid?

The distribution of test scores often forms a normal (bell-shaped) curve around the central average score, with fewer and fewer scores at the extremes.

Standardization establishes a basis for meaningful score comparisons by giving a test to a representative sample of future test-takers. Reliability is the extent to which a test yields consistent results (on two halves of the test, on alternative forms of the test, or when people are retested). Validity is the extent to which a test measures or predicts what it is supposed to. A test has content validity if it samples the pertinent behavior (as a driving test measures driving ability). It has predictive validity if it predicts a behavior it was designed to predict. (Aptitude tests have predictive ability if they can predict future achievements; their predictive power is best for the early school years.)

The Dynamics of Intelligence

10-7 How stable are intelligence test scores over the life span, and how does aging affect crystallized and fluid intelligence?

Cross-sectional studies (comparing people of different ages) and longitudinal studies (retesting the same group over a period of years) have shown that fluid intelligence declines in older adults, in part because neural processing slows. However, crystallized intelligence tends to increase.

The stability of intelligence test scores increases with age. At age 4, scores fluctuate somewhat but begin to predict adolescent and adult scores. By early adolescence, scores are very stable and predictive.

10-8 What are the traits of those at the low and high intelligence extremes?

At the low extreme are those with unusually low scores. An intelligence test score of or below 70 is one diagnostic criterion for the diagnosis of intellectual disability; other criteria are limited conceptual, social, and practical skills. One condition included in this category is Down syndrome, a developmental disorder caused by an extra copy of chromosome 21.

People at the high-intelligence extreme tend to be healthy and well-adjusted, as well as unusually successful academically. Schools sometimes “track” such children, separating them from students with lower scores. Such programs can become self-fulfilling prophecies as both groups live up to—or down to—others’ perceptions and expectations.

Genetic and Environmental Influences on Intelligence

10-9 What evidence points to a genetic influence on intelligence, and what is heritability?

Studies of twins, family members, and adoptees indicate a significant hereditary contribution to intelligence scores. Intelligence seems to be polygenetic, and researchers are searching for genes that exert an influence. Heritability is the proportion of variation among individuals that can be attributed to genes.

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10-10 What does evidence reveal about environmental influences on intelligence?

Studies of twins, family members, and adoptees also provide evidence of environmental influences. Test scores of identical twins raised apart are slightly less similar (though still very highly correlated) than the scores of identical twins raised together. Studies of children raised in extremely impoverished environments with minimal social interaction indicate that life experiences can significantly influence intelligence test performance. No evidence supports the idea that normal, healthy children can be molded into geniuses by growing up in an exceptionally enriched environment.

10-11 How and why do the genders differ in mental ability scores?

Males and females tend to have the same average intelligence test scores, but they differ in some specific abilities. Girls are better spellers, more verbally fluent, better at locating objects, better at detecting emotions, and more sensitive to touch, taste, and color. Boys outperform girls at spatial ability and related mathematics, though in math computation and overall math performance, boys and girls hardly differ. Boys also outnumber girls at the low and high extremes of mental abilities. Evolutionary and cultural explanations have been proposed for these gender differences.

10-12 How and why do racial and ethnic groups differ in mental ability scores?

Racial and ethnic groups differ in their average intelligence test scores. The evidence suggests that environmental differences are responsible for these group differences.

10-13 Are intelligence tests inappropriately biased?

Aptitude tests aim to predict how well a test-taker will perform in a given situation. So they are necessarily “biased” in the sense that they are sensitive to performance differences caused by cultural experience. By “inappropriately biased,” psychologists mean that a test predicts less accurately for one group than for another. In this sense, most experts consider the major aptitude tests unbiased. Stereotype threat, a self-confirming concern that one will be evaluated based on a negative stereotype, affects performance on all kinds of tests.