Relationships between factors of intelligence and brain volume

The recent explosion of studies aimed at determining the biological basis of intelligence has revealed that cognitive ability has a strong biological substrate. This study expands on this literature by examining the relation between cognitive ability and MRI-measured brain volume and head size in a sample of adult male siblings recruited from the London, Ontario community in Canada. It was found that brain volume correlated with IQ at 0.35 (P<0.01), thus replicating the results of past studies. Corrections for restriction of range and attenuation in both this and past studies suggest that the population value of the brain volume-IQ correlation is closer to 0.50. Head size variables, with one exception, also showed the expected positive correlations with IQ. The results of a vector analysis on factor scores indicated that the more highly g-loaded a test was the more highly it correlated with brain volume (r=0.59, P<0.01). The sum of the data suggested that although brain volume (and to a lesser extent, head size) is predictive of g, fluid ability, and memory, it does not predict crystallized ability. Unexpectedly, the higher the spatial imaging loading of a test, the less its correlation with brain volume (vector correlation=−0.84, P<0.001).     

Investigating cognitive transfer within the framework of music practice: genetic pleiotropy rather than causality

The idea of far transfer effects in the cognitive sciences has received much attention in recent years. One domain where far transfer effects have frequently been reported is music education, with the prevailing idea that music practice entails an increase in cognitive ability (IQ). While cross‐sectional studies consistently find significant associations between music practice and IQ, randomized controlled trials, however, report mixed results. An alternative to the hypothesis of cognitive transfer effects is that some underlying factors, such as shared genes, influence practice behaviour and IQ causing associations on the phenotypic level. Here we explored the hypothesis of far transfer within the framework of music practice. A co‐twin control design combined with classical twin‐modelling based on a sample of more than 10,500 twins was used to explore causal associations between music practice and IQ as well as underlying genetic and environmental influences. As expected, phenotypic associations were moderate (r = 0.11 and r = 0.10 for males and females, respectively). However, the relationship disappeared when controlling for genetic and shared environmental influences using the co‐twin control method, indicating that a highly practiced twin did not have higher IQ than the untrained co‐twin. In line with that finding, the relationship between practice and IQ was mostly due to shared genetic influences. Findings strongly suggest that associations between music practice and IQ in the general population are non‐causal in nature. The implications of the present findings for research on plasticity, modularity, and transfer are discussed.     

Revisiting predictive bias of cognitive ability tests against Hispanic American job applicants

Previous studies have concluded that cognitive ability tests are not predictively biased against Hispanic American job applicants because test scores generally overpredict, rather than underpredict, their job performance. However, we highlight two important shortcomings of these past studies and use meta-analytic and computation modeling techniques to address these two shortcomings. In Study 1, an updated meta-analysis of the Hispanic–White mean difference (d-value) on job performance was carried out. In Study 2, computation modeling was used to correct the Study 1 d-values for indirect range restriction and combine them with other meta-analytic parameters relevant to predictive bias to determine how often cognitive ability test scores underpredict Hispanic applicants’ job performance. Hispanic applicants’ job performance was underpredicted by a small to moderate amount in most conditions of the computation model. In contrast to previous studies, this suggests cognitive ability tests can be expected to exhibit predictive bias against Hispanic applicants much of the time. However, some conditions did not exhibit underprediction, highlighting that predictive bias depends on various selection system parameters, such as the criterion-related validity of cognitive ability tests and other predictors used in selection. Regardless, our results challenge “lack of predictive bias” as a rationale for supporting test use.     

Accounting for the shared environment in cognitive abilities and academic achievement with measured socioecological contexts

Behavioral and molecular genetic research has established that child cognitive ability and academic performance are substantially heritable, but genetic variation does not account for all of the stratification of cognitive and academic outcomes across families. Which specific contexts and experiences contribute to these shared environmental influences on cognitive ability and academic achievement? Using an ethnically and socioeconomically diverse sample of N = 1728 twins ages 7–20 from the Texas Twin Project, we identified specific measured family, school, and neighborhood socioecological contexts that statistically accounted for latent shared environmental variance in cognitive abilities and academic skills. Composite measures of parent socioeconomic status (SES), school demographic composition, and neighborhood SES accounted for moderate proportions of variation in IQ and achievement. Total variance explained by the multilevel contexts ranged from 15% to 22%. The influence of family SES on IQ and achievement overlapped substantially with the influence of school and neighborhood predictors. Together with race, the measured socioecological contexts explained 100% of shared environmental influences on IQ and approximately 79% of shared environmental influences on both verbal comprehension and reading ability. In contrast, nontrivial proportions of shared environmental variation in math performance were left unexplained. We highlight the potential utility of constructing “polyenvironmental risk scores” in an effort to better predict developmental outcomes and to quantify children's and adolescents’ interrelated networks of experiences. A video abstract of this article can be viewed at: https://youtu.be/77E_DctFsr0     

Gender and its contribution to the prediction of cognitive abilities at 5 years

Gender-related differences in the prediction of five year-olds' cognitive abilities from measures of distal environment, proximal environment and infant test scores were examined in a random sample of 93 boys and 90 girls. Distal environmental data included maternal IQ, maternal and paternal education. Proximal environmental data included two variables derived from the Home Screening Questionnaire: the Home Questions and the Toy Checklist. The Bayley MDI was administered at age 13 months, whereas WPPSI-R was used as cognitive outcome measure at age 5 years. The relationship between paternal education and child IQ, and between proximal environmental variables and child IQ was significantly stronger for boys than for girls. The associations between proximal environment and IQ in boys, were accounted for by the distal environmental variables. Bayley MDI correlated significantly higher with girls' IQ compared to boys' IQ. Findings are discussed in terms of parental gender-differentiated socialization processes.     

The difference isn't black and white: stereotype threat and the race gap on Raven's Advanced Progressive Matrices

This study addresses recent criticisms aimed at the interpretation of stereotype threat research and methodological weaknesses of previous studies that have examined race differences on Raven's Advanced Progressive Matrices (APM). African American and White undergraduates completed the APM under three conditions. In two threat conditions, participants received either standard APM instructions (standard threat) or were told that the APM was an IQ test (high threat). In a low threat condition, participants were told that the APM was a set of puzzles and that the researchers wanted their opinions of them. Results supported the stereotype threat interpretation of race differences in cognitive ability test scores. Although African American participants underperformed Whites under both standard and high threat instructions, they performed just as well as Whites did under low threat instructions.     

Traditional Healing as Indigenous Knowledge: Its Relevance to HIV/AIDS in Southern Africa and the Implications for Counselors

This article integrates the results of several culture-based studies conducted over the past decade. Specifically, links are made between the continued relevance of the African traditional healer's corpus of knowledge, the efficacy of the healer's cultural authority, and the need for HIV/AIDS-related strategies and interventions that are culturally sensitive, especially counseling. Results of an initial investigation of traditional healing in Lesotho, Swaziland, and Zimbabwe are integrated with more recent research in Botswana and Namibia. Findings from these studies are meshed with preliminary results of an ongoing investigation of the contextual influences and cultural factors associated with the spread of HIV/AIDS in the southern African region. Outcomes of the combined investigations have supported further examination of traditional healing as an indigenous knowledge system, of its relevance to HIV/AIDS, and of its significance to professional counselors in Africa. Related recommendations are offered for consideration by those working within HIV/AIDS systems of intervention.     

Children's cognitive ability from 4 to 9 years old as a function of prenatal cocaine exposure, environmental risk, and maternal verbal intelligence

This study examined the effects of prenatal cocaine exposure, environmental risk, and maternal verbal intelligence on children's cognitive ability. Gender and age were examined as moderators of potential cocaine exposure effects. The Stanford-Binet IV intelligence test was administered to 231 children (91 cocaine exposed, 140 unexposed) at ages 4, 6, and 9 years. Neonatal medical risk and other prenatal exposures (alcohol, cigarettes, and marijuana) were also examined for their unique effects on child IQ. Mixed models analysis indicated that prenatal cocaine exposure interacted with gender, as cocaine-exposed boys had lower composite IQ scores. Age at assessment did not moderate this relation, indicating that cocaine-exposed boys had lower IQs across this age period. A stimulating home environment and high maternal verbal IQ also predicted higher composite IQ scores. Cocaine-exposed boys had lower scores on the Abstract/Visual Reasoning subscale, with trends for lower scores on the Short-Term Memory and Verbal Reasoning subscales, as exposure effects were observed across domains. The findings indicate that cocaine exposure continues to place children at risk for mild cognitive deficits into preadolescence. Possible mechanisms for the Exposure x Gender interaction are discussed.     

Neuropsychological characteristics of children with the 22q11 Deletion Syndrome: a descriptive analysis.

Previous reports of cognitive functioning in children with the 22q11 Deletion Syndrome have reported marked variability in IQ and achievement subtest scores. Studies have begun to explore neuropsychological function in 22q11 DS however results are inconsistent and the profile incomplete. We assessed 40 children ages 5-12 with 22q11 DS. Consistent with past results, visual-spatial memory was significantly lower than verbal memory. Differentially lowered scores were found only in visual attention, working memory and motor function. Contrary with some past results quantitative, verbal ability, and visual spatial memory scores were within 1 SD from the standardization sample mean. Motor behavior, not typically discussed with regard to 22q11 DS school-age children, may be critical to incorporate in neurocognitive studies of children with 22q11 DS. Implications of these findings are considered with regard to past results.     

Adoption Is a Successful Natural Intervention Enhancing Adopted Children's IQ and School Performance

ABSTRACT— Is the cognitive development of adopted children different from that of (a) children who have remained in institutional care or in their birth families or (b) their current (environmental) nonadopted siblings or peers? We attempt to answer these questions on the basis of a meta-analysis of 62 studies including 17,767 adopted children. Compared to their nonadopted siblings or peers who stayed behind, adopted children scored substantially higher on IQ tests and they performed much better at school. Compared to their current nonadopted environmental peers or siblings, adopted children showed similar IQ scores but their school performance and language abilities lagged somewhat behind. Most importantly, we found a twofold increase in special-education referrals in adopted children compared to their nonadopted peers. Taken together, the findings document the positive impact of adoption on children's cognitive development and adopted children's remarkably normal cognitive competence but somewhat delayed school performance.     

A systematic literature review of the average IQ of sub-Saharan Africans

On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit Publishers.] concluded that the average IQ of the Black population of sub-Saharan Africa lies below 70. In this paper, the authors systematically review published empirical data on the performance of Africans on the following IQ tests: Draw-A-Man (DAM) test, Kaufman-Assessment Battery for Children (K-ABC), the Wechsler scales (WAIS & WISC), and several other IQ tests (but not the Raven's tests). Inclusion and exclusion criteria are explicitly discussed. Results show that average IQ of Africans on these tests is approximately 82 when compared to UK norms. We provide estimates of the average IQ per country and estimates on the basis of alternative inclusion criteria. Our estimate of average IQ converges with the finding that national IQs of sub-Saharan African countries as predicted from several international studies of student achievement are around 82. It is suggested that this estimate should be considered in light of the Flynn Effect. It is concluded that more psychometric studies are needed to address the issue of measurement bias of western IQ tests for Africans.     

On historicity,context and the existence of African philosophy

Abstract

The author reviews the second edition of Philosophy from Africa by comparing it with the first edition and with other anthologies in African philosophy. Questions regarding the existence and identity of African philosophy receive special attention. It is argued that a negation of the existence of African philosophy results from monolithic, ahistorical and decontextualized thinking about Africa and about philosophy. The roots and development of African philosophy are inseparably bound up with the continent’s historical, political, cultural and economic complexities. The challenge facing African philosophers is twofold: deconstructing the notion of philosophy as constructed and conceived by the West; and reconstructing the history of African philosophy.     

Adoption and cognitive development: a meta-analytic comparison of adopted and nonadopted children's IQ and school performance

This meta-analysis of 62 studies (N=17,767 adopted children) examined whether the cognitive development of adopted children differed from that of (a) children who remained in institutional care or in the birth family and (b) their current (environmental) nonadopted siblings or peers. Adopted children scored higher on IQ tests than their nonadopted siblings or peers who stayed behind, and their school performance was better. Adopted children did not differ from their nonadopted environmental peers or siblings in IQ, but their school performance and language abilities lagged behind, and more adopted children developed learning problems. Taken together, the meta-analyses document the positive impact of adoption on the children's cognitive development and their remarkably normal cognitive competence but delayed school performance.     

Are apparent sex differences in mean IQ scores created in part by sample restriction and increased male variance?

This study investigated the possibility that apparent sex differences in IQ are at least partly created by the degree of sample restriction from the baseline population. We used a nationally representative sample, the 1970 British Cohort Study. Sample sizes varied from 6518 to 11,389 between data-collection sweeps. Principal components analysis of scores obtained on four cognitive tests administered at age 10 was used to obtain estimates that we name ‘IQ’. These age-10 scores were then used to estimate the sex differences at age 10, and also among participants in the two later waves, at age 26 and 30. At age 10, there was a small but significant advantage for boys (Cohen’s d = 0.081). Boys had greater variability in these IQ scores. We then investigated how this very small male advantage at 10 changed with sample restriction. We used the same IQs obtained at age 10, but considered only those subjects who returned for data-collection sweeps at ages 26 and 30 years. Subjects returning at age 26 and 30 were more likely to be females and to have higher age-10 IQ scores. Attrition at age 30 was 28% and the male advantage in IQ scores increased by 15%. Attrition at age 26 was 43% and the male advantage in IQ scores increased by 48%. The findings underline the importance of monitoring attrition in longitudinal studies, as well as emphasising the need for representative samples in studying sex differences in intelligence. A proportion of the apparent male advantage in general cognitive ability that has been reported by some researchers might be attributable to the combination of greater male variance in general cognitive ability and sample restriction, though this remains to be tested in a sample with an appropriate mental test battery.     

Researching HIV/AIDS,Education & Childhood in the African Context

This article offers a reflective review of 12 articles and 4 brief reports included in this special issue of the International Journal of Psychology in Africa with the theme, ‘HIV/AIDS, education and childhood in the African context’. Muthukrishna and Ramsuran (2007) have emphasised that the consequences of HIV/AIDS can be far-reaching for children and young people resulting in unequal life chances. It is thus fitting that this special issue should be edited by them in KwaZulu-Natal, South Africa, in the country (and province) with the highest levels of incidence of HIV/AIDS in Africa. In this article I offer a commentary on how the interpretive lenses of the authors who are located in various disciplines provide a theorised understanding of what shapes knowledge constructions in situated African contexts.     

Implications of the Cattell-Horn-Carroll theory on ethnic differences in IQ

The Cattell-Horn-Carroll theory of intelligence and the Spearman-Jensen hypothesis were applied to help interpret mean IQ differences among ethnic groups. The Cattell-Horn-Carroll theory classifies cognitive abilities on three strata, which differ by magnitude of generality including specific, broad, and general abilities. The Spearman-Jensen hypothesis advances the belief that mean IQ differences between African Americans and Euro-Americans occur as a function of the test's g loadings. Although IQ differences between African Americans and Euro-Americans occur, the differences should be larger on tests with higher g loadings and smaller on tests with lower g loadings. The analysis described in this paper may serve as the catalyst to encourage all intelligence test publishers to supply test users with data regarding mean IQ differences among various ethnic groups.     

Are Shunt Revisions Associated with IQ in Congenital Hydrocephalus? A Meta -Analysis

Although it is generally acknowledged that shunt revisions are associated with reductions in cognitive functions in individuals with congenital hydrocephalus, the literature yields mixed results and is inconclusive. The current study used meta-analytic methods to empirically synthesize studies addressing the association of shunt revisions and IQ in individuals with congenital hydrocephalus. Six studies and three in-house datasets yielded 11 independent samples for meta-analysis. Groups representing lower and higher numbers of shunt revisions were coded to generate effect sizes for differences in IQ scores. Mean effect size across studies was statistically significant, but small (Hedges’ g = 0.25, p < 0.001, 95 % CI [0.08, 0.43]) with more shunt revisions associated with lower IQ scores. Results show an association of lower IQ and more shunt revisions of about 3 IQ points, a small effect, but within the error of measurement associated with IQ tests. Although clinical significance of this effect is not clear, results suggest that repeated shunt revisions because of shunt failure is associated with a reduction in cognitive functions.     

Migratory selection for inversely related covariant T-, and IQ-Nexus traits: Testing the IQ/T-Geo-Climatic-Origin theory by the General Trait Covariance model

The IQ/T-Geo-Climatic Origin (GCO) theory admits that primordial northbound migration out of Africa increasingly demanded higher IQ and decreased aggression as temperatures sank. To organisms with a fixed intra-systemic energy budget, this meant that small-brained – High T (Lo-IQ/Hi-T)” masculine aggressive A5 males became too “expensive” in cold eco-niches, and were replaced by Low Testosterone androgyne A1 (Hi-IQ/Lo-T) light-weight males with sufficient energy for developing the large energy-greedy brain needed for survival during cold winters. The physiological re-balancing of T-Nexus and IQ-Nexus traits probably occurred during migration over the past 40,000 years.     

Is body mass index in old age related to cognitive abilities? The Lothian Birth Cohort 1936 Study

We tested the hypothesis that the previously reported association between a higher body mass index (BMI) and poorer cognition in later adulthood is an artifact of confounding by previous cognitive ability and socioeconomic status. Participants were 1,079 adults aged about 70 years in the Lothian Birth Cohort 1936 Study, on whom there are IQ data from age 11. Cognitive outcome measures included: IQ at age 70 using the same test that was administered at age 11; composite measures of general cognitive ability (g factor), speed of information processing, and memory; and two tests of verbal ability. People classified as overweight or obese in later adulthood had significantly lower scores on tests of childhood IQ, age 70 IQ, g factor, and verbal ability. There was no significant association with processing speed or memory performance. After adjusting for childhood IQ and social class in general linear models, associations with age 70 IQ and g factor were nonsignificant or attenuated. However, throughout the models, there was a persistent (inverse) relationship between BMI and performance on the National Adult Reading Test (NART) and Wechsler Test of Adult Reading (WTAR), which remained significant after full adjustment for all sociodemographic and health covariates (for the NART, p = .025; for the WTAR, p = .011). The findings suggest that the previously reported BMI-cognition associations in later adulthood could be largely accounted for by prior ability and socioeconomic status, and by the possible influence of these factors on the adoption of health behaviors in adulthood.     

Attention deficit,conduct, oppositional,and anxiety disorders in children: III. Laboratory differences

Children aged 5–13 years with DSM-III diagnoses of Attention Deficit (ADDH), Anxiety, (ANX), or Conduct plus ADDH (HC) Disorder and matched normal controls were compared on a set of laboratory measures of impulsivity, arousal, motor performance, activity level, and cognition, and on behavior ratings during testing. While ANX patients did not differ from their controls, ADDH and HC patients did on Verbal IQ, most of the behavior ratings, and on about one-third of the test variables. ANX patients were about 1 year older, and more likely to be female, than ADDH and HC patients. When age, sex, and verbal IQ effects were partialed out, very few differences among the three diagnostic groups remained. The importance of precise control of such variables is emphasized and the impact of the failure to do so in past studies is discussed. The question is raised whether the deficit in verbal IQ is not so much a defect of matching as the essential feature of ADDH from which most of the other commonly reported cognitive symptoms stem.This research was supported by the Medical Research Council of New Zealand.