History: defining & measuring intelligence

1. History: defining & measuring intelligence • Sir Francis Galton (1822-1911) • genes & family lines • intelligence = biological capacity • reaction times & sensory acuity • later research contradicted these measures

2. History: defining & measuring intelligence • Alfred Binet (1857-1911) • Binet-Simon Test France, 1905 • intelligence = collection of higher-order mental abilities loosely related to one another • intelligence is nurtured • mental age

3. History: defining & measuring intelligence • Charles Spearman (1863-1945) • liked Binet’s methods of testing • liked Galton’s idea that intelligence was a single entity • developed “factor analysis” • two factors • “g” = general intelligence • “s” = specific ability • score on any given test depends on a combination of these 2 factors • g accounts for the similarity in test results • s accounts for the differences in test results

4. History: defining & measuring intelligence • Raymond Cattell (1905 - ) • student of Spearman’s • modified Spearman’s intelligence theory • thought that general intelligence was not one factor but two

5. Cattell’s Fluid & Crystallized Intelligence • Fluid intelligence • ability to perceive relationships without previous specific experience • matrices tests or verbal analogies

6. Cattell’s Fluid & Crystallized Intelligence • Crystallized intelligence • mental ability derived from previous experience • word meanings • use of tools • cultural practices

7. Modern intelligence tests • The Stanford-Binet Scale • modification of the original Binet-Simon, after original came to US • intelligence quotient (IQ) = child’s mental age divided by child’s chronological age • used widely in the US, not as much as previously

8. Modern intelligence tests • The Wechsler tests • used more widely now than Stanford-Binet • modeled after Binet’s, also made adult test • WISC-III for children • WAIS-III for adults

9. 68.26% Number of score 95.44% 0.13% 0.13% 13.59% 34.13% 34.13% 13.59% 2.14% 2.14% 50 70 85 100 115 130 145 Wechsler IQ score Standardized scoring of Wechsler tests • All raw scores converted to standardized scores • Normal distribution • Mean of 100 • Standard deviation of 15

10. How valid are IQ tests? • Validity = test measures what it’s intended to measure • Does test correlate with other measures of same construct? • School achievement • IQ tests (I.e., S-B and the Wechsler) correlate highly • but they were designed to test stuff that you learn in school • Prestigious positions • On-the-job performance & other work-related variables

11. What do IQ tests measure about your mind? • Mental speed and span of working memory • typically use a digit span test to measure this • more recent studies find significant correlations between reaction times and IQ scores • Why is this important? • mental quickness may expand capacity of working memory

12. What do IQ tests measure about your mind? • Mental self-government • Sternberg • studies more complex decision-making abilities • states that the mind is made up of different components, each of which works on different problem solving tasks

13. Nature vs. Nurture in IQ • Are differences between people due to environmental or genetic differences? • Misunderstanding the question • “Is a person’s intelligence due more to genes or to environment?” • no genes = no intelligence • both genes & intelligence crucial for any trait

14. Group A Group B Length Length Width Width Nature vs. Nurture in IQ • Rectangle analogy • is a rectangle’s area due more to its width or its length? • are differences in area among rectangles due more to differences in their length or in their width?

15. Heritability & Environmentality • Heritability • degree to which variation in trait stems from genetic, rather than environmental, differences among individuals • Environmentality • degree to which variation is due to environmental rather than genetic differences

16. The Heritability Coefficient • Single number, ranging from 0 to 1.0 • Represents amount of trait due to genetic differences • 0 means no variance due to genetics • 1 means all variance due to genetics • .30 means 30% is due to genetic differences, 70% due to environmental

17. Twin Studies & Family Influence • If trait genetic: • closely related more similar than less closely related • Many close relatives share environments too • Types of studies to separate effects • monozygotic twins reared together • monozygotic twins reared apart • siblings/dizygotic reared together • siblings/dizygotic reared apart • adoptive siblings reared together

18. Identical twins Fraternal twins Family Influence on IQ • Transient influence of family in which you are raised • adoptive siblings as children and adults • identical vs. fraternal twins reared together

19. IQ Differences among Racial/Cultural Groups • Find differences among racial & cultural groups on IQ • American Blacks score about 15 points lower than Whites • WHY? • genetics? • Witty & Jenkins (1935) • No support for genetic differences • environment?

20. IQ Differences among Racial/Cultural Groups • Each wheat field planted from same package of genetically diverse seeds • One field is quite fertile, the other is not • Within each field, differences due to genetics • Between each field, differences due to environment (fertility)

21. Why differences between Blacks & Whites? • Social designation influences • autonomous minorities • deliberately separate themselves • immigrant minorities • came to country to better lives • see selves as better than those left behind • involuntary minorities • did not choose minority status • routinely judged as inferior by dominant majority • cross-cultural findings on IQ scores

22. IQ Scores Year Historical increase in IQ • Improved performance on IQ tests over the years • Big increases in tests assessing fluid intelligence, smallest in factual knowledge • Increased schooling only accounts for small portion of this increase • Due to changes in the culture?

23. Summary • Nature vs. nurture debate • heritability vs. environmentality • studies of twins & family influence • Racial & cultural differences in IQ • why we can’t interpret differences as due to genetics • what we can attribute the differences to • Historical increase in IQ scores