A term referring to a variety of mental capabilities, including the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience.
Throughout the 20th century scientists have debated the nature of intelligence, including its heritability and whether (and to what extent) it exists or is measurable. The 1994 publication of Richard J. Herrnstein and Charles Murray's volume The Bell Curve brought these debates to the forefront of public attention by discussing links between social class, race, and IQ scores, despite the fact that many have questioned the validity of IQ tests as a measurement of intelligence or a predictor of achievement and success.
Although the assessment of mental abilities through standardized testing has had many detractors, especially over the past 30 years, the notion that intellect is a measurable entity--also called the psychometric approach--lies at the heart of much modern theorizing about the nature of intelligence. A rudimentary forerunner to 20th-century intelligence testing was developed in the 1860s by Charles Darwin's younger cousin, Sir Francis Galton, who, inspired by On the Origin of Species, set out to prove that intelligence was inherited, using quantitative studies of prominent individuals and their families. Galton's work was followed in 1905 by that of French psychologist Alfred Binet, who introduced the concept of mental age, which would match chronological age in children of average ability. It would exceed chronological age in bright children and would be below in those of lesser ability. Binet's test was introduced to the United States in a modified form in 1916, and with it the concept of the intelligence quotient (mental age divided by chronological age and multiplied by 100).
In the meantime, one of the central concepts of the psychometric approach to intelligence had been introduced in England in 1904 by Charles Spearman, who had noted that people who perform well on one type of intelligence test tend to do well on others also. Spearman gave a name to the general mental ability that carried over from one type of cognitive testing to another--g for general intelligence--and ultimately decided that it consisted mainly of the ability to infer relationships based on one's experiences. Although the concept of g has the disadvantage of being based solely on a particular statistical analysis rather than direct observation, it has remained an important part of psychometric research.
Psychometrics is still considered by many to be a valid scientific area of inquiry, but it has been challenged by researchers who approach intelligence in different ways. Instead of studying the structure of intelligence (i.e., what it is) some scientists have focused on the processes involved (how it works). A leader in this information-processing approach is Robert Sternberg, whose triarchic theory of intelligence not only addresses internal thought processes but also explores how an individual uses them to solve problems within his or her environment. The first part of Sternberg's theory, like psychometric theories, is concerned with the internal components of intelligence, although its emphasis is on process rather than structure. It analyzes the processes involved in interpreting sensory stimuli, storing and retrieving information in short- and long-term memory, solving problems, and acquiring new skills. The second part of the triarchic theory addresses the interaction between mental processes and experience, centering on the fact that, while a new experience requires complex mental responses, as it becomes increasingly familiar, the required response gradually becomes routine and automatic. In the third part of his theory, Sternberg analyzes the way that people use their intelligence to survive in the "real world" by either adapting to their environments, modifying them, or abandoning them in favor of new ones.
Another approach is Howard Gardner's theory of multiple intelligences, which replaces the general intelligence factor (g ) with seven different types of intelligence: linguistic; logical-mathematical; spatial; interpersonal (ability to deal with other people); intrapersonal (insight into oneself); musical; and bodily-kinaesthetic (athletic ability). According to Gardner, each of these areas of competence includes a separate set of problem-solving skills that can be mobilized by various symbolic systems. Every person has all the different types of intelligence, although some may be developed far more fully than others. (The most dramatic example of this is found in savants, mentally retarded people with exceptional abilities in a few highly specialized areas, usually involving calculations.)
Gardner regards his theory as radical in its rejection of g and in its reliance on psychometric premises. He claims that g (a purported general intelligence factor enabling people to perform fairly consistently on different types of mental tests) is an artificial construct made possible by the fact that standard IQ tests assess only the first three of the seven types of intelligence, ignoring the others. He also argues that IQ tests can predict school performance only because formal education emphasizes those abilities measured by the tests, rather than truly assessing all aspects of human intelligence. In recent years, Gardner's theory has become popular among educators, and a number of schools have instituted programs based on his ideas.
Another focus for recent studies of intelligence has been the evolutionary development of the brain . Scientists with this research orientation are interested in the ways that human mental capacities developed over hundreds of thousands of years or more in response to changing problem-solving challenges in the environment. From this perspective, the g factor of the psychometricians could be viewed as a specialized ability that has evolved in response to our expanded exposure to tests of all kinds rather than an innate ability that enables us to deal with them. An evolutionary perspective on the phenomenon of similar performance in a variety of cognitive tests might also take into account the selective pairing of cognitively matched couples that has resulted from the modern freedom to marry for love, producing children whose abilities are more and more likely to be uniformly high or low across a series of different cognitive tasks.
Although IQ tests are still widely used in the United States, there has been increasing doubt voiced about their ability to measure the mental capacities that determine success in life. IQ testing has also been criticized for being biased with regard to race and gender. In modern times, the first scientist to test mental ability was Alfred Binet, a French psychologist who devised an intelligence test for children in 1905, based on the idea that intelligence could be expressed in terms of age. Binet created the concept of "mental age," according to which the test performance of a child of average intelligence would match his or her age, while a gifted child's performance would be on par with that of an older child, and a slow learner's abilities would be equal to those of a younger child. Binet's test was introduced to the United States in a modified form in 1916 by Lewis Terman. The scoring system of the new test, devised by German psychologist William Stern, consisted of dividing a child's mental age by his or her chronological age and multiplying the quotient by 100 to arrive at an "intelligence quotient" (which would equal 100 in a person of average ability).
The Wechsler Intelligence Scales, developed in 1949 by David Wechsler, addressed an issue that still provokes criticism of IQ tests today: the fact that there are different types of intelligence. The Wechsler scales replaced the single mental-age score with a verbal scale and a performance scale for nonverbal skills to address each test taker's individual combination of strengths and weaknesses. The Stanford Binet and Wechsler tests (in updated versions) remain the most widely administered IQ tests in the United States. Average performance at each age level is still assigned a score of 100, but today's scores are calculated solely by comparison with the performance of others in the same age group rather than test takers of various ages. Among the general population, scores cluster around 100 and gradually decrease in either direction, in a pattern known as the normal distribution (or "bell") curve.
Although IQ scores are good predictors of academic achievement in elementary and secondary school, the correspondence between IQ and academic performance is less consistent at higher levels of education, and many have questioned the ability of IQ tests to predict success later in life. The tests don't measure many of the qualities necessary for achievement in the world of work, such as persistence, self-confidence, motivation, and interpersonal skills, or the ability to set priorities and to allocate one's time and effort efficiently. In addition, the creativity and intuition responsible for great achievements in both science and the arts are not reflected by IQ tests. For example, creativity often involves the ability to envision multiple solutions to a problem (a trait educators call divergent thinking ); in contrast, IQ tests require the choice of a single answer or solution to a problem, a type of task that could penalize highly creative people.
The value of IQ tests has also been called into question by recent theories that define intelligence in ways that transcend the boundaries of tests chiefly designed to measure abstract reasoning and verbal comprehension. For example, Robert Steinberg's triarchical model addresses not only internal thought processes but also how they operate in relation to past experience and to the external environment. Harvard University psychologist Howard Gardner has posited a theory of multiple intelligences that includes seven different types of intelligence: linguistic and logical-mathematical (the types measured by IQ tests); spatial; interpersonal (ability to deal with other people); intrapersonal (insight into oneself); musical; and bodily-kinaesthetic (athletic ability).
Critics have also questioned whether IQ tests are a fair or valid way of assessing intelligence in members of ethnic and cultural minorities. Early in the 20th century, IQ tests were used to screen foreign immigrants to the United States; roughly 80% of Eastern European immigrants tested during the World War I era were declared "feeble-minded," even though the tests discriminated against them in terms of language skills and cultural knowledge of the United States. The relationship between IQ and race became an inflammatory issue with the publication of the article "How Much Can We Boost IQ and Scholastic Achievement?" by educational psychologist Arthur Jensen in the Harvard Educational Review in 1969. Flying in the face of prevailing belief in the effects of environmental factors on intelligence, Jensen argued that the effectiveness of the government social programs of the 1960's War on Poverty had been limited because the children they had been intended to help had relatively low IQs, a situation that could not be remedied by government intervention. Jensen was widely censured for his views, and standardized testing underwent a period of criticism within the educational establishment, as the National Education Association called for a moratorium on testing and major school systems attempted to limit or even abandon publicly administered standardized tests. Another milestone in the public controversy over testing was the 1981 publication of Stephen Jay Gould's best-selling The Mismeasure of Man, which critiqued IQ tests as well as the entire concept of measurable intelligence.
Many still claim that IQ tests are unfair to members of minority groups because they are based on the vocabulary, customs, and values of the mainstream, or dominant, culture. Some observers have cited cultural bias in testing to explain the fact that, on average, African-Americans and Hispanic-Americans score 12-15 points lower than European-Americans on IQ tests. (Asian-Americans, however, score an average of four to six points higher than European-Americans.) A new round of controversy was ignited with the 1994 publication of The Bell Curve by Richard Herrnstein and Charles Murray, who explore the relationship between IQ, race, and pervasive social problems such as unemployment, crime, and illegitimacy. Given the proliferation of recent theories about the nature of intelligence, many psychologists have disagreed with Herrnstein and Murray's central assumptions that intelligence is measurable by IQ tests, that it is genetically based, and that a person's IQ essentially remains unchanged over time. From a sociopolitical viewpoint, the book's critics have taken issue with The Bell Curve 's use of arguments about the genetic nature of intelligence to cast doubt on the power of government to remedy many of the nation's most pressing social problems.
Yet another topic for debate has arisen with the discovery that IQ scores in the world's developed countries--especially scores related to mazes and puzzles--have risen dramatically since the introduction of IQ tests early in the century. Scores in the United States have risen an average of 24 points since 1918, scores in Britain have climbed 27 points since 1942, and comparable figures have been reported throughout Western Europe, as well in Canada, Japan, Israel, Australia, and other parts of the developed world. This phenomenon--named the Flynn effect for the New Zealand researcher who first noticed it--raises important questions about intelligence testing. It has implications for the debate over the relative importance of heredity and environment in determining IQ, since experts agree that such a large difference in test scores in so short a time cannot be explained by genetic changes.
A variety of environmental factors have been cited as possible explanations for the Flynn effect, including expanded opportunities for formal education that have given children throughout the world more and earlier exposure to some types of questions they are likely to encounter on an IQ test (although IQ gains in areas such as mathematics and vocabulary, which are most directly linked to formal schooling, have been more modest than those in nonverbal areas). For children in the United States in the 1970s and 1980s, exposure to printed texts and electronic technology--from cereal boxes to video games--has been cited as an explanation for improved familiarity with the types of maze and puzzle questions that have generated the greatest score changes. Improved mastery of spatial relations has also been linked to video games. Other environmental factors mentioned in connection with the Flynn effect include improved nutrition and changes in parenting styles.
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