Describes results of several studies of the neurochemical determinants of inspection time (IT), outlining the significance of several studies in which performance on the IT task is measured before and after modulating key human central nervous system neurotransmitters and receptor systems. Results of these studies suggest a primarily cholinergic…

This biography explores the many scientific interests and contributions of Francis Galton and outlines his psychological studies as a "detour" from his major works that lasted from 1877 to 1885. Galton's interest in heredity was a focus of the second half of his life, the first having concentrated on geography and exploration. (SLD)

Makes the case that "g" (general intelligence) can arise from the effect of shared genes influencing cognitive test performance and provides a simple mathematical demonstration of how this occurs. Predicts the need for a profound shift in the search for biological bases of "g." (Author/SLD)

Used the classical twin design with 390 pairs of twins to study the influence of genetic factors on the large phenotypic variation in inspection time (IT) and whether the well-established IT-IQ association could be explained by a common genetic factor. Findings provide potentially important information for the biological bases of the…

Finds several difficulties with the theory advanced by R. Howard and shows that alternative explanations relating to changes in the chess environment, including increased access to chess knowledge, offer better explanations for the increased presence of young players at top-level chess. (SLD)

Raw IQ scores do not demonstrate the bell curve created by normalized scores, even the bell-shaped distribution does not require large numbers of underlying genes. Family data support a major gene locus of IQ. The correlation between glutathione peroxidase and IQ should be investigated through molecular genetics. (SLD)

Brain size and cerebral glucose metabolic rate were determined for 10 individuals with mild mental retardation (MR), 7 individuals with Down syndrome (DS), and 10 matched controls. MR and DS groups both had brain volumes of about 80% compared to controls, with variance greatest within the MR group. (SLD)

Data from a previous adoption study using the Wechsler Intelligence Scale for Children-Revised show that the genetic effect is reflected by psychometric "g" (general intelligence) to a greater degree than is the environmental effect. This finding is consistent with the hypothesis that "g" largely reflects the genetic component…

Data from 236 pairs of black twins and white twins aged 13-17 years were used to examine genetic and environmental factors influencing cranial size, an indirect estimate of brain volume. Genetic factors are required to account for the phenotypic variance in cranial capacity. (SLD)

The relationship between mental retardation and brain size is discussed. Research suggests that a common path for many otherwise idiopathic mild retardation cases (genetic or environmental) could be small brain size, indicating reduced information processing capacity. Suggestions are made for further research on neuron number. (SLD)

Used prospective data to examine the relationship between the family environment and child and adolescent achievement and to determine genetic and environmental contributions to this relationship. Data from 2,108 sibling full- and half-sibling pairs from the National Longitudinal Survey of Youth suggest that genetic factors explain about…

Studies with 65 adults found two new visual processing tasks, visual change detection and visual movement detection, to be correlated with inspection time and the nonverbal scores from the Alice Helm 4 test of general intelligence. Results are discussed in terms of the correlation between inspection time and intelligence and the psychobiological…

Uses data from the National Longitudinal Survey of Youth for 1,943 full siblings and 129 half-siblings to study genetic and shared environmental influences on IQ, education, and income. Results suggest that social inequality in the United States has its origins in genetically based traits and in different environmental backgrounds. (SLD)

To study whether individual differences in general cognitive ability differ in males and females, full-scale IQ data from 426 child twin pairs were fitted to a structural equation model of sex limitation. Individual differences in general cognitive ability appear to be substantially due to common genetic influences in males and females. (SLD)

Used steady-state probe topography to investigate the cortical activity of 12 average and 12 high IQ Australian college students during a spatial working memory task. Results, in terms of changes in visual evoked potentials, suggest that the areas of the brain involved in working memory are influenced by individual differences in intelligence.…