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Chapter 11

Chapter 11: Intelligence

Chapter Review

INTELLIGENCE TESTING

  • Alfred Binet, the originator of intelligence tests, sought to identify children who would benefit from remedial education. Binet understood intelligence to be a general attribute, applicable to a very wide range of mental tasks. He measured intelligence by means of a comparison between a child’s mental age and her chronological age.
  • Intelligence tests have been developed for various uses, including the WAIS. This test has high test-retest reliability, even with gaps of many decades between the first test and subsequent tests. The test also seems valid, as indicated by correlations between IQ and academic performance, job performance, and other measurements.

WHAT IS INTELLIGENCE? THE PSYCHOMETRIC APPROACH

  • The psychometric approach to intelligence seeks to understand intelligence by scrutinizing patterns among the test scores. One aspect of this approach is an examination of how different elements within the test are intercorrelated. These intercorrelations are readily observed, suggesting that all of the diverse subtests within the IQ test overlap in the abilities they are assessing. This finding is confirmed by factor analysis, which isolates the common element in all the subtests. That element is often referred to as general intelligence, or g.
  • A hierarchical notion of intelligence places g at the top of the hierarchy; at the next level are verbal ability, quantitative ability, and spatial ability. Correlations between these abilities provide evidence for g. The stronger correlations within these more specific categories tell us there are also more specialized forms of intelligence.
  • Fluid g is the ability to deal with new and unusual problems; crystallized g refers to someone’s accumulated knowledge and skills. These two forms of intelligence are correlated, but they’re also distinguishable in several ways. Fatigue and aging, for example, have a much greater impact on fluid intelligence than on crystallized intelligence.

THE BUILDING BLOCKS OF INTELLIGENCE

  • One mechanism that contributes to intelligence is simply mental speed: Higher-IQ individuals show faster response times in many tasks, including tasks measuring inspection time.
  • Another contribution to intelligence is working memory capacity—an ability to keep multiple goals in mind, and also an ability to control one’s own attention. This capacity may allow the construction of more complex task models; it may also allow greater executive control over one’s own thoughts. These points fit well with the P-FIT theory of intelligence, which suggests that intelligence depends on the integrated functioning of many brain sites including those in the parietal and frontal lobes.

INTELLIGENCE BEYOND THE IQ TEST

  • Some investigators have concerned themselves with certain aspects of the term intelligence that go beyond IQ, such as practical intelligence. A related approach has led to measures of emotional intelligence; people with this sort of intelligence have fewer conflicts with their peers and are more tolerant of stress.
  • A different proposal rests on the notion of multiple intelligences, which is buttressed by evidence from studies of brain lesions and people with savant syndrome.
  • Our understanding of intelligence may also need to take into account the cultural context. People in different cultures have different abilities as well as a different understanding of the test-taking situation.

THE ROOTS OF INTELLIGENCE

  • Intelligence-test performance is determined by both environmental and genetic factors. Evidence for the role of genetic factors includes the fact that the correlation between the IQs of identical (monozygotic) twins is higher than that for fraternal twins, and also the observation that the correlation between their IQ scores is remarkably high even when identical twins are reared apart. Further evidence for a hereditary contribution comes from adopted children, whose IQs correlate more highly with the IQs of their biological parents than with the IQs of their adoptive parents. At the same time, however, evidence for environmental effects is provided by increases and decreases in the mean IQ of populations whose cultural or educational level has risen or fallen. Environmental effects are also clearly implicated by the worldwide improvement in IQ scores observed over the last few decades.
  • The relative weight of genetic and environmental factors in determining the variation of a given characteristic is given by the heritability ratio, or H. The value of H depends in part on the given population, for H describes only the degree to which the variability within that particular population can be attributed to genetic variance.
  • In recent years, much interest (and debate) has focused on IQ differences among different groups of individuals— including a comparison between men and women, and a comparison between American whites and American blacks. Men and women do not differ in overall IQ, but men on average seem to have a small advantage in some tasks requiring visuospatial reasoning; women on average have a small advantage in some verbal tasks. These differences are certainly fostered by a cultural environment in which boys and girls have different types of experiences and receive types of encouragement.
  • Several studies have documented a 10- to 15-point difference between average scores of American whites and blacks. This difference does not seem attributable to genetic factors. Part of the difference derives from the poverty and disadvantaged circumstances in which many American blacks live; part can be attributed to the effects of stereotype threat.
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