Quiz Practice

Question 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 that the heritability of IQ is somewhere between .4 and .8
• heritability can take practically any value for any trait depending on the relative variability of genetic endowment and environment in the population being studied
• We can only definitively say that heritability factors between 0 and 1

Question 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

• As SES increased, the contribution of shared environment diminished and the contribution of genes increased, crossing in lower middle-class families.
• Highest heritability contribution in high SES families
• The effects are strongest in the USA, but less pronounced in European countries (such as the netherlands)
• The effects are strongest in young children (under 5) and weakest/mixed in adults

Question 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 may tend to underestimate the role of environment due to the restricted social class range of adoptive homes.
• Adoptive families are generally of relatively high SES, environments of adoptive families are much more supportive of intellectual growth than are those of nonadoptive families
• Since environment has a larger impact on outcomes among lower SES individuals, then removing them from the sample not only reduces the variance of environment but also reduces the average impact of environment on outcomes in the sample, thereby causing a reduction in the measured role of environment for two separate reasons

Question 4

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

Answer 4

• One interpretation of the finding that heritability of IQ is very low for lower SES individuals is that children in poverty do not get to develop their full genetic potential
• Intervention study by Turkheimer et al. 2012; The Infant Health and Development Program (IHDP)
  
  • Measured the level of heritiability in enriched vs control low SES children.
  • Heritabilities were significant (>0) in the intervention group on seven of eight tests and were higher in the intervention group than in the control group on all seven

Question 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

• Whereas 282 individual genes responsible for specific forms of mental retardation have been identified, very little progress has been made in finding the genes that contribute to normal variation
• A recent study found 6 genetic markers, which needed extreme statistical lability to be significant and together explained only 1% of total variance

Question 6

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

Answer 6

• Technical problems in specifying the genetic sequence.
  
  • Linkage methods have low statistical power, only identify regions not genes.
  • Genome wide association studies are limited to the common groups of chromosomal markers that are dense and complex to unpack
  • Assumes additivity of gene sequences and ignores interactions and non-linear relationships
• Broader problems involving the prediction of complex human behavior more generally
  
  • The number of genes involved is likely to be massive and require huge numbers of participants

Question 7

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

Answer 7

• Breastfeeding may increase IQ by as much as 6 points for infants born with normal weight and by as much as 8 points for those born prematurely
• One meta-analysis found only a 3-point effect of breastfeeding on IQ when social class and IQ of the mother were controlled.
• Second study found almost no effect on academic achievement scores when the mother’s IQ was controlled

Question 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

• Caspi et al., 2007
  
  • 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.
  • It was only the child’s allele at the relevant site, not the mother’s, that mediated the influence on Iife
• Catalan 2002 Animal study
  
  • 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

What is the effect of adoption on the IQ of the adopted child? Why?

Answer 9

• Adoption adds 12–18 points to the IQ of unrelated children, who are usually from lower SES backgrounds
• Higher SES Environments
  
  • Home environments are correlated with neighborhood, peer, and school environments.
  • Greater levels of cognitive socialisation in higher SES families
• But we have no direct evidence of the impact of any particular environmental factor on IQ

Question 10

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

Answer 10

• Vocabulary: 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, the child of unemployed African American mothers has heard 10 million words
• Encouraging words to reprimands ratio: professional parents 6:1, working-class parents 2:1, and unemployed African American mothers 1:2.

Question 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

• most if not all twin studies, especially studies of adults, likely result in higher estimates of genetic effects and lower estimates of environmental effects
• This is because lower SES individuals are difficult to recruit to laboratories and testing sites
• Self-selection: The lower SES individuals who volunteer may resemble higher SES individuals on variables relevant to overestimation of heritability effects
• Failure to take into account assortive mating - may further ofset environmental factors

Question 12

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

Answer 12

• There is a difference in IQ of 3 points in early adulthood favoring firstborn children over later-born children that may be understandable in terms of differences in the home environment
• The difference is based on social order not birth order
  
  • Indicated by the fact that second-born children in families in which the firstborn child died early in life have IQs as high as firstborns at age 18

Question 13

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

Answer 13

• Natural experiments in which children are deprived of school for an extended period of time show deficits in IQ of as much as 2SD.
• Children who miss a year of school show a drop of several points in IQ
• 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
• Natural experiment 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

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 elementary school unless children are then placed in average or above-average schools
• Children in the Milwaukee Project (Garber, 1988) program had an average IQ 10 points higher than those of controls when they were adolescents
• By adulthood, individuals who had participated in such interventions were
  
  • about half as likely to have repeated a grade
  • Half as likely to be assigned to special education classes
  • Far more likely to have completed high school, attended college, and own their own home
• The discrepancy between school achievement effects and IQ effects (after early elementary school) is sufficiently great to suggest to some that the achievement effects are produced more by attention, self-control, and perseverance gains than by intellectual gains

Question 15

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 15

• A meta-analysis of a large number of studies 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 0.5SD for the elderly (more for those past age 65 than for those younger).
• It is possible to begin cardiovascular exercise as late as the seventh decade of life and substantially reduce the likelihood of Alzheimer’s disease

Question 16

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

Answer 16

• Countries
  
  • Nations that have recently begun to modernize, such as Kenya and the Caribbean nations show extremely high rates of gain,
  • Nations where modernization such as Brazil began during the early to mid-20th century show large and persistent gains
  • Results for nations that began modernization as far back as the 19th century are slower, and suggest that its effects on IQ can reach an asymptote
  • Likely caused by the social requirements of the industrial revolution
• Types of ability
  
  • Gains on fluid intelligence showed substantially greater gains than crystallized intelligence
  • Largest on Ravens Progressive Matrices, Similarities subtests
  • Least in arithmatic, crystalline intelligence
    *

Question 17

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 17

• The nutrition hypothesis posits 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
• Not all countries showed higher growth in the lower half
• Norway showed higher growth in height for the top half, but higher IQ gains in the lower half - It is unlikely that enhanced nutrition over time had a positive effect on IQ but a negative effect on height

Question 18

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 18

• Very large gains
  
  • In Ravens Progressive matrices (2SD),
  • Similarities subtests & performance subtests
• Reasonable Gains
  
  • Comprehension (slightly larger gains in adults)
• Little Gain
  
  • Arithmetic (adults and children)
• Information and vocabulary have increased substaintially in adults but not children

Question 19

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

Answer 19

• The prefrontal cortex (PFC) involves fluid reasoning, executive function and working memory tasks, measured by Raven’s Progressive Matrices
• Damage Studies
  
  • Damage to the PFC show fluid functioning is dramatically reduced (as measured by above tests) while crystalline intelligence remains virtual unaffected
• Neuroimaging studies
  
  • found that performance on fluid reasoning tasks (like Raven’s Progressive Matrices), is dependent on neural circuitry associated with the PFC

Question 20

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

Answer 20

• Neural efficiency is based on research that 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 are related to task difficulty in a manner characterized by an inverted U shape
  
  • As task difficulty increases, high-ability individuals exhibit increasing neural activity in PFC, whereas lower ability individuals exhibit decreasing activity

Question 21

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

Answer 21

• Taxis and the hippocampus; mediates navigation in three-dimensional space.
  
  • London taxicab drivers have hippocampi that are enlarged
  • Enlarged in proportion to the amount of time they have been on the job
• Juggling; 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, with the extent of growth correlating with skill. Three months after ceasing to juggle, the size of gray matter expansions was reduced.
• Tetris; Three months of playing the visual-spatial game Tetris resulted in increases in cortical thickness in two regions and also in functional changes

Question 22

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

Answer 22

• No evidence was found for overall IQ differences between sexes when a full range of tests is administered,
• Similarly no differences were found in quantitative abilities, and no difference in fluid reasoning
• Females have an advantage for verbal and perceptual abilities such as fluency and memory
• Males have advantage on visuospatial abilities such as object rotation

Question 23

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

Answer 23

• The gap in performance can be mostly eliminated when both genders are trained in visuospatial video games, or primed with positive reinforcement of intelligence.
• The gap in performance widened when subjects were primed on gender

Question 24

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

Answer 24

• On average, the male brain is between 8% and 14% larger than the female brain (Similar to the heart and kidney).
• In general, females have more gray matter and males have more white matter in different regions of the brain
• Brain size does not plausibly account for differences in aspects of intelligence because
  
  • all areas of the brain are not equally important for cognitive functioning,
  • different patterns of gray and white matter correlate with intelligence for males and females

Question 25

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

Answer 25

• The Asian Americans had about the same mean IQ as White Americans (actually slightly lower) but scored one third of a standard deviation higher on the SAT than did White Americans
• SAT scores may reflect motivational differences—for example, taking more and higher level math courses—to a greater degree than do IQ tests
• An endemic belief in East Asian 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.

Question 26

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

Answer 26

• The individual multiplier involves a dynamic interplay between genetic potential/ability and the environment.
  
  • Better than average ability accesses an enriched environment, which enhances the ability advantage, which accesses an even more enriched environment, and so forth.
  • This accounts for the similarity in outcome for twins that masks SES differences
• The Social multiplier involves a second kind of dynamic interaction whereby
  
  • the rising mean (some people learn to shoot with either hand) encourages every individual to improve (more people begin to shoot with either hand), which raises the mean further, which influences the individual further,
  • Explains a great escalation of skills over time in society (flynn effect) re: industrial revolution demands for qualifications

Question 27

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 27

• McArdle and colleagues (2000) found that fluid ability does not predict crystallized ability (operationalized as vocabulary) in individuals, but memory does, and memory is somewhat influenced by fluid ability
• Ferrer and McArdle (2004) used a broader set of measures of crystallized ability. They found no evidence that fluid abilities predict changes in vocabulary in individuals, but they did find that fluid ability predicted academic knowledge and quantitative abilities
• Hambrick et al. 2009 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 28

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

Answer 28

• A child can eat a marshmallow in front of them immediately or wait and receive 2 later
• Older students (8th grade) were given $1 in an envelope and allowed to spend it or exchange it for $2 a week later
• Self-discipline and ability to delay gratification predicted success across a variety of academic measures such as academic performance and learning gains.

Question 29

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

Answer 29

• 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
• A study by Eccleston (2011) indicates that even stress on the pregnant mother may have enduring effects on her children
  
  • boys gestating during or after 9/11 were 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
• Sharkey (2010) found that Black children living in Chicago (ages 5–17) scored between 0.5 and 0.66 SD worse on tests in the aftermath of a homicide in their neighborhood

Question 30

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

Answer 30

• School Performance: There is a significant correlation between high IQ scores and final school grades (eg SAT)
• Career Performance:
  
  • High correlation of high IQ with people in professional jobs such as lawyers and doctors.
  • Within jobs, IQ predicts promotion and senior positions