** Intelligence tutorial test

Question 1

1. What is heritability? What is the estimated heritability of intelligence?

Answer 1

Heritability is the proportion of variability in a phenotype that is accounted for by variation in genotype.

Most studies estimate the heritability of IQ as somewhere between .4 and .8 (generally less for children).

However, there is no single “true” value for the heritability of intelligence, as the heritability of a trait depends on the relative variances of the predictors – genotype and environment. In humans, who don’t live in a controlled environment, variability of this predictor is uncontrolled.

Question 2

2. Which SES groups show higher heritability of intelligence according to the “heritability by SES” hypothesis? Which countries and age groups show the strongest and weakest evidence for the hypothesis?

Answer 2

High-SES individuals show higher heritability of intelligence than low-SES individuals.

This has been demonstrated on samples in America, but studies of European countries such as Britain and the Netherlands have failed to confirm this interaction consistently.

Many studies have documented the SES by heritability interaction in children, but only one of several has been able to observe it in adults. This suggests the interaction may not persist beyond childhood.

Question 3

3. Compared to other methods, are adoption studies likely to over-estimate or under-estimate the role of the environment in predicting intelligence? Why?

Answer 3

Adoption studies are likely to underestimate the role of environment due to the restricted social class range of adoptive homes, which are generally high SES and more supportive of intellectual growth than nonadoptive homes.

The restriction of range (as much as 70% in some studies) means that the possible magnitude of correlations between adoptive parents’ IQ and that of their children is curtailed.

Since environment has a larger impact on outcomes among lower SES individuals, removing them from the sample 1) reduces the variance of environment 2) reduces the average impact of environment, thereby causing a reduction in the measured role of environment.

Thus excluding participants from the lowest SES levels biases the results by omitting the portion of the distribution for which environmental effects are known to be strongest.

Question 4

4. What possible explanation for the “heritability by SES” hypothesis is suggested in the reading? Describe the study that supports this explanation.

Answer 4

One explanation is that low-SES children do not get to develop their genetic potential.

Support for this hypothesis is offered by the Infant Health and Development Program (IHDP) – a broad-based intervention program designed to improve the cognitive function and school performance of approx. 1,000 low birth weight infants. When tested at 96 months, the heritabilities of the intervention group were significantly higher than the control group on 7/8 of a wide battery of tests, including the WISC and Raven’s.

Question 5

5. What is the research evidence for specific genes underlying differences in intelligence? Is this different for the normal ranges of intelligence and the prediction of mental retardation?

Answer 5

There is scant evidence that intelligence can be accounted for by specific genes. A genome-wide scan using 7,000 subjects (Butcher et al., 2008) found only six genetic markers (SNPs) associated with cognitive ability, and only one of these was statistically significant. When the six markers were considered together they barely explained 1% of the variance in general cognitive ability.

Prediction of mental retardation is more successful – 282 individual genes responsible for specific forms of mental retardation have been identified (Inlow & Restifo, 2004).

Question 6

6. The article suggests several reasons why it may be difficult to identify the specific genes responsible for genetic variation in intelligence. Give at least three of these reasons.

Answer 6

1. Technology is not advanced enough to be able to find trends in genetic sequences, identify specific genes, and their associations with traits and behaviours.
2. The number of genes involved in an outcome as complex as intelligence is very large, and therefore the contribution of any individual locus is just as small as the number of genes is large and thus very difficult to detect without huge samples.
3. A linear specification of the genetic sequence may not capture all of the information contained in the genome. Statistical interactions or nonlinear associations among genes, or between genes and particular environments, could foil an effort to understand intelligence by simply adding up the small effects of many genes.

Question 7

7. What are the effects of breastfeeding on IQ? Are there confounding variables that might explain these effects?

Answer 7

Studies have reported an increase in IQ of as much as 6 points for infants born with normal weight and as much as 8 points for those born prematurely. The advantage seems to persist into adulthood.

Social class and IQ may be confounding variables. When social class and IQ of the mother is controlled for, a metaanalysis generated the reduced score of a 3-point effect of breastfeeding on IQ. Another found essentially no effect on academic achievement scores when the mother’s IQ was controlled for except for a modest effect for children breastfed for more than seven months.

Question 8

8. The paper describes two genetic/biological studies that account for some of the effect of breastfeeding on the child’s IQ. Describe: (a) the genetic contingency in the effects of breastfeeding on IQ; and (b) the animal modeling study

Answer 8

An important study indicates that breastfeeding is effective in raising IQ by about six points, but only for the large portion of the population having one of two alleles at a particular site that regulates fatty acids and is influenced by breast milk.

Human breast milk contains fatty acids that are not found in formula and that have been shown to prevent neurological deficits in mice.

Question 9

9. What is the effect of adoption on the IQ of the adopted child? What explanation does the paper give for this effect?

Answer 9

It raises it, on average, by 12 points (compared siblings left with birth parents or children adopted by lower SES parents).

This is likely to environmental differences that are associated with social class, given that adoption typically moves children from lower to higher SES homes.

In these high SES homes, children are in an environment more likely be supportive of intellectual growth than that of nonadoptive families.

Question 10

10. What are the two main differences between high and low SES home environments according to the Hart and Risley (1995) study?

Answer 10

1. The amount parents talk to children. Hart and Risley (1995) showed that the child of professional parents has heard 30 million words by the age of three, the child of working-class parents has heard 20 million words, and the vocabulary is much richer for the higher SES child. The child of unemployed African American mothers has heard 10 million words by the age of three.
2. The ratio of encouraging comments made to children versus reprimands. The child of professional parents received six encouragements for every reprimand, the child of working-class parents received two encouragements per reprimand, and the child of unemployed African-American mothers received two reprimands per encouragement.

Question 11

11. According to the paper, do twin studies over-estimate or under-estimate the heritability of intelligence? Why does the paper propose that this is the case?

Answer 11

Twin studies tend to overestimate heritability of intelligence.

This is because of a bias in samples towards higher SES individuals. The reasons for this are that lower SES individuals are difficult to recruit and the lower SES individuals who volunteer may resemble higher SES individuals on variables relevant to overestimation of heritability effects.

Since heritability is higher in high SES children, who dominate the sample, the heritability estimate is skewed upwards.

Question 12

12. What are the effects of birth order on IQ? What evidence is there that these effects are social rather than biological?

Answer 12

Despite many studies on this subject there is a lack of consensus that birth order affects IQ, although a recent –and particularly rigorous – study indicates an IQ advantage of 3 points for firstborn children over later-born children.

Evidence that these effects are social rather than biological is provided by studies showing that second-born children in families in which the firstborn child died early in life have IQs as high as firstborns at age 18. Thus genetic or gestational factors do not account for the difference in IQ. A possible explanation for a birth-order effect on IQ is that the intellectual environment of the firstborn is superior to that of the later-born because the firstborn has the full attention of the parents for a period of time.

Question 13

13. Name at least three sources of evidence that attending school increases IQ scores.

Answer 13

1. Natural experiments in which children are deprived of school for an extended period of time show deficits in IQ of as much as 2 SD.
2. A child who enters fifth grade approximately a year earlier than a child of nearly the same age who enters fourth grade will have a Verbal IQ more than 5 points higher at the end of the school year (Cahan & Cohen, 1989) and as much as 9 percentiles higher in eighth grade.
3. A natural experiment was created in Norway when an extra two years of schooling beyond the seventh grade began to be required. Effects on IQ were substantial at age 19.

Question 14

14. What are the effects of early intervention programs on IQ? What are the other effects of early intervention programs?

Answer 14

The best prekindergarten programs for lower SES children have a substantial effect on IQ, but this typically fades by late primary school, perhaps because the environments of the children do not remain enriched.

If lower-SES children are placed in average or above-average elementary schools following the prekindergarten interventions, children have scored an average IQ 10 points higher than those of controls when they were adolescents. Another study reported IQs of 4.5 points higher than those of controls when individuals were 21 years old.

By adulthood, individuals who had participated in interventions such as the Abecedarian project were about half as likely to have repeated a grade in school or to have been assigned to special education classes and were far more likely to have completed high school, attended college, and even to own their own home.

Question 15

15. Which three aspects of intelligence are stimulant drugs known to affect?

Answer 15

Stimulant drugs have been shown to give modest enhancements in attention, working memory and executive function in healthy, normal adults.

Question 16

16. Does aerobic exercise affect any aspects of intelligence/IQ? What does the evidence say about the size of the effects and the group that is affected?

Answer 16

A meta-analysis has shown that aerobic exercise, at least for the elderly, is very important for maintaining IQ, especially for executive functions such as planning, inhibition, and scheduling of mental procedures.

The effect of exercise on these functions is more than 0.5 SD for the elderly (and more for those elderly past age 65 than for those younger).

Question 17

17. Which countries show the largest and smallest Flynn effects? Why? Which type of ability shows the largest Flynn effect?

Answer 17

The largest Flynn effect has been observed in Kenya and the Caribbean nations, and the smallest in Sweden, where studies show IQ to have peaked or even in mild decline.

The explanation given is that the Flynn effect is greater in nations that are still modernizing, such as Kenya, and slows once modernization has been reached, as is the case in Sweden.

In Flynn’s 2007 review, gains on tests generally considered to measure fluid intelligence showed substantially greater gains (18 points in IQ-equivalence terms) than tests considered to measure crystallized intelligence (10 points).

Question 18

18. The article suggests that better nutrition is NOT likely to be the reason for the Flynn effect. What logical argument does the article propose for this? What sources of evidence support this argument?

Answer 18

If nutrition accounts for the Flynn effect, one would expect to see greater IQ gains in the lower half of the IQ distribution than the upper half because one would assume that even in the past the upper classes were well fed, whereas the nutritional deficiencies of the lower classes have gradually diminished.

IQ gains have indeed been concentrated in the lower half of the curve for some countries (Denmark, Spain, and Norway), but not for others (France, the Netherlands, and the United States). Norway is actually a counterexample: height gains were larger in the upper half of their distribution, whereas IQ gains were higher in the lower half. It is unlikely that enhanced nutrition over time had a positive effect on IQ but a negative effect on height.

In the developed world, nutrition has been a more or less constant factor since 1950, which does not account for the increases in IQ.

Question 19

19. Subtests of the Wechsler scales show different susceptibility to the “Flynn effect”. Which subtests have the largest and smallest gains, and which of these are consistent across the life span?

Answer 19

The largest gains have been found on the Raven’s Progressive Matrices – nearly 2 SD in the period from 1947 to 2002. Also large gains on the Similarities, Performance and Comprehension subtest. There have been only small gains for arithmetic for both adults and children.
On the Information and Vocabulary subtests, adult gains have outstripped children’s gains, which may reflect the influence of increased tertiary education and more cognitively demanding work roles.

Question 20

20. Which type of intelligence test scores are associated with the pre-frontal cortex? Give two forms of evidence for this association.

Answer 20

Fluid reasoning, executive function and working memory tasks are associated with activity in the prefrontal cortex (PFC).

Individuals with damage to PFC show profound impairment on reasoning tasks such as the Raven’s Progressive Matrices – while other aspects of mental ability associated with crystallized intelligence remain intact.

Neuroimaging studies have demonstrated that performance on fluid reasoning such as Raven’s is dependent on neural circuitry associated with the PFC – although consistency across studies in brain areas associated with reasoning, however, is limited.

Question 21

21. What is the neural efficiency hypothesis? How does neural efficiency differ across intelligence levels and task difficulty?

Answer 21

The hypothesis is that individuals of higher ability exhibit greater efficiency at the neural level. That is, high-ability individuals are able to solve simple and moderately difficult problems more quickly and with less cortical activity, particularly in PFC, than lower ability individuals.

Relations between neural activity and intelligence, however, are related to task difficulty in a manner characterized by an inverted U shape. That is, for a simple or moderately difficult task cortical activity is lowest for those of highest and lowest ability and most for those of medium ability.

However, when task difficulty was matched to ability level, individuals with high g(F) exhibited increased brain activity relative to individuals with low g(F). As task difficulty increases, high-ability individuals exhibit increasing neural activity in PFC, whereas lower ability individuals exhibit decreasing activity.

Question 22

22. Identify and describe three pieces of evidence in favour of a reciprocal relationship between intellectual functioning and brain morphology?

Answer 22

1. London taxicab drivers have hippocampi that are enlarged – and enlarged in proportion to the amount of time they have been on the job (Maguire et al., 2000).
2. The process of learning how to juggle over a three-month period increased the size of gray matter in the mid-temporal area and the left posterior intra-parietal sulcus. The extent of structural gray matter growth was correlated with increased juggling ability. Three months after ceasing to juggle, the size of gray matter expansions was reduced.
3. Three months of playing the visual-spatial game Tetris resulted in increases in cortical thickness in two regions and also in functional changes (though functional changes were not in the same areas as structural changes).

Question 23

23. What are the sex differences on overall IQ, fluid reasoning, visuo-spatial abilities, verbal abilities, and quantitative abilities?

Answer 23

No sex differences appear to exist in overall IQ on average, nor on fluid reasoning. There is minimal or no difference on tests of quantitative reasoning, but males’ scores are more variable, which results in more males at both the high and low ends of the distribution.

However, there are differences, on average, in individual abilities.

Females have an advantage for verbal abilities such as fluency, reading, writing and verbal aspects of memory.

Males have an advantage on visuospatial abilities such as object rotation.

Question 24

24. Name at least two sources of evidence that the male advantage on visuo-spatial skills is partly social (rather than biological) in origin.

Answer 24

1. When female and male college students were trained with computer games that required use of spatial visualization, the gap between male and female performance was reduced, but not completely eliminated.
2. When male and female college students were primed with positive stereotypes (“I’m a student from a selective college”) before taking an object rotation task, the gender gap in performance was nearly eliminated. When gender was primed before the test, the gender gap widened (McGlone & Aronson, 2006).

Question 25

25. What are the sex differences in brain size and are these linked to gender differences in IQ? Why or why not?

Answer 25

On average, the male brain is between 8% and 14% larger than the female brain.

This difference is not linked to gender difference in IQ because all areas of the brain are not equally important for cognitive functioning. There is a large degree of dimorphism in brain structure, suggesting men and women achieve similar IQ results with different brain regions. This implies there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs – including brains of different size – may manifest equivalent intellectual performance.

Question 26

26. What is the achievement gap between White and Asian Americans and what mechanism does the article propose for this gap?

Answer 26

While Asian Americans have tested about the same on IQ as White Americans, they score one third of a standard deviation higher on the SAT. Moreover, Chinese Americans who graduated high school in 1966 attained occupations of a professional, managerial, or technical nature at a rate 62% higher than White Americans. The picture that results is that Asian Americans capitalize on a given level of intellectual ability much more than do European Americans.

The explanation proposed for this effect is that East Asians are members of cultures having a Confucian background. An endemic belief in those cultures is that intelligence is primarily a matter of hard work. Families with a Confucian background exert far more influence on their children than do most families of European culture. They can demand of their children excellence in education and preparation for high-status careers and expect their children to try to comply.

Question 27

27. Give brief definitions of the “individual multiplier” and the “social multiplier” that the paper proposes as explanations of the Flynn effect.

Answer 27

The individual multiplier is the mechanism whereby identical twins raised apart access environments far more alike than those of randomly selected individuals.

E.g. If twins have slightly better brains than average, although raised apart, they are both more likely to enjoy school, get into an honors stream, go to a top university, and so forth. There is a dynamic interplay each step of the way, whereby better than average ability accesses an enriched environment, which enhances the ability advantage, which accesses an even more enriched environment, and so forth. Thanks to the individual multiplier, the fact that separated twins have powerful environmental factors in common is “masked,” and their common genes get all of the credit for their highly similar IQs.

The social multiplier is the mechanism whereby the rising mean skill at some task encourages every individual to improve, which raises the mean further, which influences the individual further, and there is a great escalation of skills over time.

If the Industrial Revolution puts a premium on credentials, and lucrative cognitive work expands, the more people in general need increased cognitive skills. This seems likely to result in increasing cognitive challenges in educational and entertainment settings and an explosion of college enrollments. Thanks to the social multiplier, the evolving environment can cause huge cognitive gains over time with no assistance from better genes.

Question 28

28. Cattell’s investment hypothesis is that fluid g (Gf) should predict the development of crystallized g (Gc). What is the empirical evidence that Gf can predict the development of Gc?

Answer 28

Evidence of a direct link is inconsistent.

One study suggests fluid ability does not predict crystallized ability (operationalized as vocabulary) in individuals, but memory does, and memory is somewhat influenced by fluid ability.

A later study failed to find evidence that fluid abilities predict changes in vocabulary in individuals, but they did find that fluid ability predicted academic knowledge and quantitative abilities.

A structural equation modeling study of gains in knowledge of current events found that g(F) predicts the initial level of knowledge and that the initial level of knowledge predicts gains, but they found no direct role for g(F) in predicting gains.

Question 29

29. Name two ways that delay of gratification has been operationalized. What does delay of gratification predict?

Answer 29

Mischel et al (1988) operationalised delay of gratification as ability to forego eating one marshmallow in order to eat two later.

Duckworth and Seligman (2005) operationalised it as the ability to not spend one dollar given in an envelope in order to receive $2 a week later.

Delay of gratification has been shown to predict a variety of academic measures including SAT scores (in the Marshmallow test) and learning gains.

Question 30

30. Name at least three forms of evidence that stress levels can affect intelligence.

Answer 30

1. Chronically high levels of stress hormones damage specific areas of the brain—namely, the neural circuitry of PFC and hippocampus—that are important for regulating attention and for short-term memory, long-term memory, and working memory.
2. Black children living in Chicago (ages 5–17) scored between 0.5 and 0.66 SD worse on tests (both the WISC-Revised and the Wide Range Achievement Test-3) in the aftermath of a homicide in their neighborhood.
3. Children born to women in New York City who were in the first six months of pregnancy when 9/11 occurred had lower birth weights than children born before 9/11 or well after it, and the boys at the age of six were more than 7% more likely to be in special education and more than 15% more likely to be in kindergarten rather than first grade.

Question 31

31. Name at least three valued life outcomes that IQ scores are known to predict.

Answer 31

Academic success
Career success – people with IQs are more likely to have professional careers as accountants, attorneys or physicians.
Performance within ones career