1 History: defining & measuring intelligence zSir Francis Galton ( ) ygenes & family lines yintelligence = biological capacity yreaction times & sensory acuity xlater research contradicted these measures

2 History: defining & measuring intelligence zAlfred Binet ( ) yBinet-Simon Test France, 1905 yintelligence = collection of higher- order mental abilities loosely related to one another yintelligence is nurtured ymental age

3 History: defining & measuring intelligence zCharles Spearman ( ) yliked Binet’s methods of testing yliked Galton’s idea that intelligence was a single entity ydeveloped “factor analysis” ytwo factors x“g” = general intelligence x“s” = specific ability yscore on any given test depends on a combination of these 2 factors xg accounts for the similarity in test results xs accounts for the differences in test results

4 History: defining & measuring intelligence zRaymond Cattell ( ) ystudent of Spearman’s ymodified Spearman’s intelligence theory ythought that general intelligence was not one factor but two

5 Cattell’s Fluid & Crystallized Intelligence zFluid intelligence yability to perceive relationships without previous specific experience ymatrices tests or verbal analogies

6 Cattell’s Fluid & Crystallized Intelligence zCrystallized intelligence ymental ability derived from previous experience xword meanings xuse of tools xcultural practices

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

8 Modern intelligence tests zThe Wechsler tests yused more widely now than Stanford- Binet ymodeled after Binet’s, also made adult test xWISC-III for children xWAIS-III for adults

9 Standardized scoring of Wechsler tests zAll raw scores converted to standardized scores zNormal distribution zMean of 100 zStandard deviation of % 13.59%34.13% 13.59%2.14% 0.13% 95.44% 68.26% Wechsler IQ score Number of score

10 How valid are IQ tests? zValidity = test measures what it’s intended to measure zDoes test correlate with other measures of same construct? zSchool achievement yIQ tests (I.e., S-B and the Wechsler) correlate highly ybut they were designed to test stuff that you learn in school zPrestigious positions zOn-the-job performance & other work-related variables

11 What do IQ tests measure about your mind? zMental speed and span of working memory ytypically use a digit span test to measure this ymore recent studies find significant correlations between reaction times and IQ scores zWhy is this important? ymental quickness may expand capacity of working memory

12 What do IQ tests measure about your mind? zMental self-government zSternberg ystudies more complex decision-making abilities ystates that the mind is made up of different components, each of which works on different problem solving tasks

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

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

15 Heritability & Environmentality zHeritability ydegree to which variation in trait stems from genetic, rather than environmental, differences among individuals zEnvironmentality ydegree to which variation is due to environmental rather than genetic differences

16 The Heritability Coefficient zSingle number, ranging from 0 to 1.0 zRepresents amount of trait due to genetic differences z0 means no variance due to genetics z1 means all variance due to genetics z.30 means 30% is due to genetic differences, 70% due to environmental

17 Twin Studies & Family Influence zIf trait genetic: yclosely related more similar than less closely related zMany close relatives share environments too zTypes of studies to separate effects ymonozygotic twins reared together ymonozygotic twins reared apart ysiblings/dizygotic reared together ysiblings/dizygotic reared apart yadoptive siblings reared together

18 Family Influence on IQ zTransient influence of family in which you are raised yadoptive siblings as children and adults yidentical vs. fraternal twins reared together Fraternal twins Identical twins

19 IQ Differences among Racial/Cultural Groups zFind differences among racial & cultural groups on IQ yAmerican Blacks score about 15 points lower than Whites zWHY? ygenetics? xWitty & Jenkins (1935) xNo support for genetic differences yenvironment?

20 IQ Differences among Racial/Cultural Groups zEach wheat field planted from same package of genetically diverse seeds zOne field is quite fertile, the other is not zWithin each field, differences due to genetics zBetween each field, differences due to environment (fertility)

21 Why differences between Blacks & Whites? zSocial designation influences yautonomous minorities xdeliberately separate themselves yimmigrant minorities xcame to country to better lives xsee selves as better than those left behind yinvoluntary minorities xdid not choose minority status xroutinely judged as inferior by dominant majority xcross-cultural findings on IQ scores

22 Historical increase in IQ zImproved performance on IQ tests over the years zBig increases in tests assessing fluid intelligence, smallest in factual knowledge zIncreased schooling only accounts for small portion of this increase zDue to changes in the culture? Year IQ Scores

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