Theories, Concepts, and Correlates of Cognitive Abilities
Since its beginnings in the research of Francis Galton, J. M. Cattell, William Stern, and other pioneer psychometricians during the late 19th and early 20th centuries, the field of differential psychology has been concerned in large measure with individual differences in cognitive abilities.1 Although it was preceded by the efforts of Galton and others to measure what they designated as intelligence, the first practical test of intelligence, or general mental ability, was constructed by Alfred Binet and Theodore Simon. Based to some extent on Binet's early speculations concerning the nature of intelligence, the Binet-Simon Intelligence Scale was a kind of hodgepodge of subtests fashioned from observations of the kinds of tasks that children are required to accomplish in school. It was originally designed to identify school children who, because of limited mental ability, could not profit sufficiently from instruction in regular school classrooms. However, the Binet-Simon Intelligence Scale and other early individual-and group-administered tests of cognitive abilities came to serve a wider range of practical and research purposes. In research contexts, these tests provided a means for assessing the cognitive abilities of individuals and for comparing the abilities of different groups of people. Subsequent developments in intelligence testing-including construction of the Wechsler series, tests for the physically handicapped, infant intelligence tests, culture-fair tests, and measures of special abilities-led to extensive research and a voluminous literature on individual and group differences in cognitive abilities. Chronological age, gender, race/ethnicity, nationality, culture, urban/rural residence, education, SES, family size, birth order, and historical era are some of the demographic variables that have been related to scores on tests of intelligence and special cognitive abilities. The influences of biological vari-
ables, such as genetics, brain structure and functioning, diet and nutrition, drugs and other chemicals, as well as climate, season of birth, and other environmental factors, have also been studied. The effects of untoward experiences and accidents on cognitive abilities; efforts to change cognitive functioning by special training, exercise, or teaching; and the effects of motivation, mental disorder, and even music on these abilities have also been investigated. However, rather than attempting to describe every research investigation on these topics conducted over the past 100 years, this chapter focuses on a few selected topics that have received fairly extensive coverage in the psychological literature and continue to do so.