General and Specific Cognitive Abilities Cognitive Abilities Specific
General and Specific Cognitive Abilities
Cognitive Abilities • Specific cognitive abilities – E. g. , verbal ability, spatial ability, memory, speed of processing • General cognitive ability (g) – Often used to be called “intelligence”
Hierarchical Models • Very prevalent in cognitive sciences • Work on the premise of interconnected levels • Different “units” in each level – Specific units might interconnect within and between levels
Hierarchy of Cognitive Ability General cognitive ability (g) Specific cognitive ability Individual tests
Interactions • Hundreds of individual psychological tests used in assessment • Moderate correlation between performance on different specific cognitive abilities – E. g. , do well on spatial, probably do well on memory
Correlations • Not empirical; correlation is not causation • Correlations can not tell why/how one factor relates to another, just the degree to which they do (or do not)
Genetic Regulation • Not really much question that there is heritability involved in cognitive ability • Specific gene and environmental control, however, is still pretty much unknown in humans • Better understanding in nonhumans – Empirical testing can be conducted
Intelligence Testing • Various intelligence (IQ) tests – Alfred Binet – Identify students needing special help – First test, 1905 – Revised to Binet-Simon (1908, 1911), then Stanford-Binet (1916)
Studies in Human Intelligence • Early adoption studies (Burks 1928; Leahy 1935) – IQ correlates higher in nonadoptive families than in adoptive families • Adopted away children’s IQ correlates with their biological parents (Skodak & Skeels 1949) – This is increasingly true as child ages • 1960 Louisville Twin Study, longitudinal study of environment and genetic effects begun
Heritability and Intelligence Correlations • First degree relatives, ~0. 45 • Adopted away children and biological parents, ~0. 25 • Sibs adopted apart, ~0. 25 • MZ, ~0. 85 • DZ, ~0. 6 • MZ raised apart, ~0. 75
Couple Complications to This… • Assortative mating • Nonadditive genetic variance
Assortative Mating • Non-random mating; when mates have similar features/characteristics • Important for our discussion • Affects estimates of heritability • In first-degree relatives can inflate heritability – E. g. , sibs are more similar in trait because parents are similar for same trait • In twins, though, can underestimate heritability – Raises DZ correlations because they’re 1 st degree relatives, so lessens difference b/t MZ and DZ twins
Nonadditive Genetic Variance • Additive genetic effects – Alleles at locus and across loci “add up” • Nonadditive effects – Effects of alleles different in presence of other alleles • Dominance – Alleles at same locus interact – E. g. , heterozygous phenotype different from homozygous dominant phenotype • Epistasis – Alleles at different loci interact to affect behaviour; phenotype of different genes suppressed or expressed • Emergenesis – Epistatic effects producing extraordinary effects; won’t be heritable due to interactive nature
General Intelligence • Charles Spearman – Schoolchildren’s grades across unrelated subjects positively correlated – Proposed “general” intelligence – Initial interpretation that variation in intelligence due to: – Factor specific to an individual mental task – A general factor, g, that governs performance on all cognitive tasks • Ignored group factors, however… need factor analysis to identify this
g-Factor • Is g real? • What is the actual interaction between specific and general cognition? • Correlations
g-Loading • Tests of cognitive ability derive most of their validity from the extent to which they measure g • g-loaded if quantifiable measure(s) of a task correlate highly with g • Primary goal of IQ tests is to create reliable and valid tests; thus, the tests tend to be intentionally g-loaded
Non-specificity • However, g not specific to any particular domain of knowledge or mental skill • Also, seems independent of cultural content • Support idea that g is real and not simply an artifact of particular opportunities to learn specific “skill sets”
Biological Correlates • • Brain size correlate with g, ~0. 4 Various brain wave activity and g, 0. 5 -0. 7 Speed of nerve conduction with g, ~0. 4 Even elementary cognitive tasks (ECTs) correlate with g (tasks like identify the colour of a light, number of figures on a page, etc. )
g • • g widely accepted Seems to have moderate to high heritability That said, less clear what g really is Single general process? – E. g. , information processing speed, executive function • Interaction/intersection of specific cognitive functions? • Frequently, g used synonymously with “intelligence”
QTL and g • Highly likely that many separate components contribute – Polygenic – Environment • Effect at what level? – Elementary properties, specific cognitive ability, general cognitive ability
Top down • Genes act directly on g – E. g. , perhaps through neural activity speed, etc. General cognitive ability Specific cognitive abilities Elementary processes Genes
Bottom Up • Genes affect each basic element of information processing – Highly reductionistic model General cognitive ability Specific cognitive abilities Elementary processes Genes
Multi-level Interaction • Unique genetic effects at each level, but also genetic effects in common across levels General cognitive ability Genes Specific cognitive abilities Genes Elementary processes Genes
Evidence • Some support for top down • Modularized view of brain function would fit well with bottom up • However, multivariate genetic analysis supports multi-level interaction – Keep in mind, this model incorporates elements from both top down and bottom up
Non-human Animal Models • Can look for g-like abilities in non-humans • Look for specific cognitive abilities that are directly comparable across species (e. g. , spatial ability)
Maze Dull/Maze Bright Mean Errors • Tolman and Tyron • Selectively bred rats for ability in maze learning • Maze bright rats showed few errors, maze dull rats many errors after few generations Maze dull 20 Maze bright 0 1 Generations 22
Heritability for Learning • Inbred strains of mice Bovet et al. (1969)
Heritability in Learning Bovet et al. (1969) • In and of itself, not that novel, unexpected, surprising • But, environmental effects can come in…
Genotype-Environment Interaction • Cooper & Zubek (1958) • Enriched, restricted, standard lab conditions • Enriched improves MD, not MB • Restricted detrimental to MB, not MD
Popularity of Mice • Mouse genome • Can test for specific gene effects – E. g. , transgenic critters • Very useful for genotype-environment interactions with respect to cognitive abilities • Obviously, more difficult in humans, but starting to get there
Caspi et al. (2007) • Children’s intellectual development • Interaction of genetic and environmental experience • Breastfeeding • IQ scores
Breastfeeding • Long-chain polyunsaturated fatty acids (LCPUFAs) – Present in human milk, absent in cow’s milk – Specifically, DHA (docosahexaenoic acid) and ARA (arachidonic acid) – Required for efficient neurotransmission, neurite outgrowth, dendritic arborization, and neuron regeneration post cell injury • DHA and ARA accumulate in human brain in early postnatal months – Higher concentrations in breastfed than formula fed infants
Effect on IQ • Breastfed children have higher IQs than non -breastfed children – Effect persists into adulthood • Not due to SES or other culture-specific factors – Important to control for, as in Western countries, higher SES is related to higher IQ, and higher SES women are more likely to breastfeed
Non-human Animal Models • Animals deprived in n-3 fatty acids show neuronal deficits in memory, sensory, and visual abilities • DHA supplementation in rodents and nonhuman primates increases DHA concentrations; enhances performance on learning, memory, and problem solving tasks
FADS 2 • Chromosome 11 candidate gene • Role in modification of dietary fatty acids • Encodes delta-6 desaturase, the rate limiting step on the metabolic pathway for ARA and DHA production • Hypothesis: cognitive advantage of breastfeeding related to genetic differences in LC-PUFA metabolism, specifically at FADS 2
Markers and Subjects • Used two SNPs – Genetic polymorphisms rs 174575 and rs 1535 – Strong linkage disequilibrium through promoter and intragenic region of FADS 2 (and also FADS 1, another gene involved in fatty acid metabolism) • Over 1000 New Zealand children born 1972 -73, IQ measures at age 7, 9, 11, 13 • Over 2200 children from British twins born 199495; IQ measured at age 5
IQ Outcomes and Genotype Mean IQ 110 105 New Zealand Cohort British Cohort 100 95 90 CC CG GG CC Genotypes Not breastfed CG GG Breastfed Overall, breastfed children had IQ scores 5. 6 and 6. 3 points higher than non-breastfed children in New Zealand British cohorts, respectively. About 90% either CC or CG.
Genotype and IQ • Dominant effect of C allele in response to breastfeeding • New Zealand: breastfed children with C allele showed 6. 4 IQ-point advantage (p<0. 001) compared to non-breastfed children; GG homozygotes gained no advantage from breastfeeding • British: breastfed children with C allele showed 7. 0 IQpoint advantage (p<0. 001); GG had no advantage from breastfeeding • Averaging, this equates to a 6. 8 IQ point advantage, or 0. 48 standard deviation units in the general population
rs 174575 • Genetic moderation of breastfeeding effects on IQ not likely directly due to rs 174575 – Actual molecular mechanism of influence by rs 174575 is currently unknown • May be that rs 174575 influences biosynthesis of LC-PUFAs from dietary precursors, possibly through increased transcriptional activity
Application • Earlier studies looking at neurodevelopment of infants fed DHA-supplemented vs. unsupplemented formula – Results inconclusive – Current research may offer explanation; genetic heterogeneity in fatty acid metabolism may dilute supplemental effects
Application • FADS 2 locus has not appeared on the first genome -wide scans for intelligence • Such scans identify genes with associations with phenotypes regardless of participants’ environments; ineffective for detecting genes whose effects are conditional on environmental exposure • In contemporary Western samples, significant portion of population is not breastfed; this would conceal link between FADS 2 variation and IQ
Heritability and Maturation • Early twin studies investigated development (e. g. , Galton, 1876; Merriman, 1924) • Heredity increasingly important as you develop
Developing Twins
Why • New genes come into effect • Positive feedback effect – IQ increase when adopted by parents with high IQ • Intellectual experience more self-directed as an adult • Shared environment effects decrease with age
Genetic Contributions to Developmental Change • g is pretty stable, not perfectly so… if change happens, it has a genetic aspect • Genetic effects seem to act at transitional ages – Infancy to early childhood (e. g. , language acquisition) – Early to middle childhood (e. g. , theory of mind) – Etc. Gen. factors New gen. factors Infancy Early childhood Middle childhood Shared Env.
Environment & Specific Cognition • Scarr & Weinberg (1978) • Adoption study • Little similarity for adoptive parents and adopted children or between adopted siblings on specific subsets of intelligence test… except vocabulary • Like g, specific cognitive abilities also little influenced by shared environment (i. e. , heritability significant factor)
Academic Performance • Achievement vs. ability – Semantics? • Shared environment ~60%, heritability ~30% (for 6 -12 year range) • Heritability effect does increase, and environment effect decreases with age
Heritability and Subjects From Grade 7 Report Card Grades From High School Achievement Tests Twin Correlations Subject MZ DZ History. 80. 51 Reading. 72. 57 Writing. 76. 50 Arithmetic. 81. 48 Twin Correlations Subject MZ DZ Social. 69. 52 Natural Sciences. 64. 45 English use. 72. 52 Mathematics. 71. 51
School Achievement = g? • Multivariate genetic analysis shows a common genetic effect explains much of the correlation between scores in different domains (i. e. , subjects) • Is this g, or some other measure? – Some-to-much of this is g, but some is achievement specific • Implies that achievement scores (within normal range) that are not due to ability are largely due to environment
Overall • Variance in thirds • One third of genetic variance of academic performance is in common with general cognitive ability • One third of genetic variance is general to academic performance, independent of general cognitive ability • One third is specific to each domain • Means learning abilities are not exactly the same thing genetically as general cognitive ability
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