Is g an entity? A Japanese twin study using syllogisms and intelligence tests

Using a behavioral genetic approach, we examined the validity of the hypothesis concerning the singularity of human general intelligence, the g theory, by analyzing data from two tests: the first consisted of 100 syllogism problems and the second a full-scale intelligence test. The participants were 448 Japanese young adult twins (167 pairs of identical and 53 pairs of fraternal twins). Data were analyzed for their fit to two kinds of multivariate genetic models: a common pathway model, in which a higher-order latent variable, g, was postulated as an entity; and an independent pathway model, in which the higher-order latent variable was not posited. These analyses revealed that the common pathway model which included additive genetic and nonshared environmental factors best accounted for the three distinct mental abilities: syllogistic logical deductive reasoning, verbal, and spatial. Both the substantial g-loading for syllogism-solving, historically recognized as the symbol of human intelligence, and the emergence of g as an entity at an etiological level, that is, at the genetic and environmental factor level, provide further support for the g theory.     

Gray matter and intelligence factors: Is there a neuro-g?

Heterogeneous results among neuro-imaging studies using psychometric intelligence measures may result from the variety of tests used. The g-factor may provide a common metric across studies. Here we derived a g-factor from a battery of eight cognitive tests completed by 6929 young adults, 40 of whom also completed structural MRI scans. Regional gray matter (GM) was determined using voxel-based-morphometry (VBM) and correlated to g-scores. Results showed correlations distributed throughout the brain, but there was limited overlap with brain areas identified in a similar study that used a different battery of tests to derive g-scores. Comparable spatial scores (with g variance removed) also were derived from both batteries, and there was considerable overlap in brain areas where GM was correlated to the respective spatial scores. The results indicate that g-scores derived from different test batteries do not necessarily have equivalent neuro-anatomical substrates, suggesting that identifying a “neuro-g” will be difficult. The neuro-anatomical substrate of a spatial factor, however, appears more consistent and implicates a distributed network of brain areas that may be involved with spatial ability. Future imaging studies directed at identifying the neural basis of intelligence may benefit from using a psychometric test battery chosen with specific criteria.     

Global behavioral variation: A test of differential-K

Despite Rushton’s path-breaking work into evolutionary forces affecting life history traits, not many attempts at operationalizing the differential-K spectrum at the level of countries or racial groups have been made so far. We report the construction of a “national K” factor from country-level behavioral variables. This K factor is closely related to country-level intelligence (“g”), operationalized by a composite score of IQ and scholastic achievement. We further demonstrate relationships of both g and K with measures of current environment and hypothesized evolutionary antecedents. Whereas K is predicted most powerfully by intelligence, log-transformed GDP (lgGDP) and skin reflectance, g is predicted by skin reflectance, lgGDP, cranial capacity, and a measure of evolutionary novelty.     

A smarter brain is associated with stronger neural interaction in healthy young females: A resting EEG coherence study

General intelligence, the g factor, is a major issue in psychology and neuroscience. However, the neural mechanism of the g factor is still not clear. It is suggested that the g factor should be non-modular (a property across the brain) and show good colinearity with various cognitive tests. This study examines the hypothesis that functional connectivity may be a good candidate for the g factor. We recorded resting state eyes-closed EEG signals in 184 healthy young females. Coherence values of 38 selected channel pairs across delta, theta, alpha, beta and gamma frequencies were correlated with six intelligence quotient (IQ) subtests, including symbol search, block design, object assembly, digit span, similarity and arithmetic. A three-stage analytic flow was constructed to delineate common (g factor) and unique neural components of intelligence. It is noticed that the coherence pattern demonstrates good correlation with five of the IQ subtests (except symbol search) and non-modularity in the brain. Our commonality analyses support connectivity strength in the brain as a good indicator of the g factor. For the digit span and arithmetic tests, the uniqueness analyses provide left-lateralized topography relevant to the operation of working memory. Performance on the arithmetic test is further correlated with strengths at left temporo-parietal and bilateral temporal connections. All the significant correlations are positive, indicating that the stronger the connectivity strengths, the higher the intelligence. Our analyses conclude that a smarter brain is associated with stronger interaction in the central nervous system. The implication and why the symbol search does not show parallel results are discussed.     

The g-loading of intelligence tests and their relationship with reaction times: A comment on Ruchalla et al.

Ruchalla, Schalt, and Vogel (1985) reported a negative correlation between the g-loadedness of a number of intelligence test subtests and the extent to which the subtests correlated with reaction times (RTs), a result contrary to the position of Jensen and others. A number of possible methodological problems with Ruchalla et al. are described, as are the results of two other studies pertinent to the issue. These results indicate that the g-loadedness of different subtests is in some cases highly positively correlated with the subtests' correlations with RTs, whereas in other cases the relationship is negligible or negative. The key factor appears to be the relative complexity of the RT test: more complex tests showing a strong positive correlation. In the context of these findings, Ruchalla et al.'s results are not out of line—they simply do not tell the whole story.     

When will the milk spoil? Everyday induction in human intelligence

We sought to understand (a) the mental processes underlying everyday predictive and postdictive judgements involving objects undergoing either change or no change of state over time and (b) the relation of these processes to intelligence. Forty adult (nonstudent) participants were asked to solve 40 induction problems, each presented in four forms, for a total of 160 test items. Half of the items involved predictions and half involved postdictions; within each of these two categories, half of the items involved a state change from present to future (prediction) or past (postdiction), and half did not. In addition, each participant completed convergent-discriminant psychometric ability tests measuring inductive reasoning, deductive reasoning, and vocabulary.Prediction was performed more rapidly than postdiction, but was also more susceptible to errors of judgement. Judgements involving change of state were more rapid and less error-prone than were judgements involving no change. A single information-processing model was useful for describing performance on both prediction and postdiction problems. A quantification of stimulus variables affecting performance via this model (with six predictor variables) provided a good account of participants' response latencies. Response latencies showed convergent and discriminant validity, exhibiting rather high correlations with inductive reasoning, but not with deductive reasoning. The paradigm we used thus seems to provide one useful approach to understanding the relationship of everyday induction to human intelligence, and to provide a complement to the more abstract kinds of problems—such as analogies, classifications, series completion, and matrix problems—typically used to test inductive-reasoning abilities, as an aspect of intelligence.     

The link between deductive reasoning and mathematics

ABSTRACT

Recent studies have shown that deductive reasoning skills (including transitive and conditional inferences) are related to mathematical abilities. Nevertheless, so far the links between mathematical abilities and these two forms of deductive inference have not been investigated in a single study. It is also unclear whether these inference forms are related to both basic maths skills and mathematical reasoning, and whether these relationships still hold if the effects of fluid intelligence are controlled. We conducted a study with 87 adult participants. The results showed that transitive reasoning skills were related to performance on a number line task, and conditional inferences were related to arithmetic skills. Additionally, both types of deductive inference were related to mathematical reasoning skills, although transitive and conditional reasoning ability were unrelated. Our results also highlighted the important role that ordering abilities play in mathematical reasoning, extending findings regarding the role of ordering abilities in basic maths skills. These results have implications for the theories of mathematical and deductive reasoning, and they could inspire the development of novel educational interventions.     

The ubiquity of g

We obtained the g-loading (unrotated first principal-component loading) of each of the cognitive ability measures used in the Hawaii Family Study of Cognition (HFSC) for each of the three major ethnic groups (Americans of European ancestry (AEA), Americans of Japanese ancestry (AJA) and homeland Koreans) who took part in the HFSC. The degree to which given tests (corrected for reliability) loaded on g was highly correlated with the association of cognitive test scores with the educational and occupational attainments of members of both the parent and offspring generations, with the degree of resemblance of spouses and biological relatives, and with the degree to which parental education and occupation predicted offspring cognitive test performance. For AEA and AJA families g was not found to be related to degree of mean within-sibship skew for each cognitive test, but was positively correlated with the degree of ‘hybrid vigor’ manifested by offspring of cross-ethnic matings. The above results suggest that g, as opposed to the non-g components of intelligence, is more influenced by additive genetic factors, although this is confounded by assortative mating for g, but provide only weak support for the hypothesis that g is more influenced by directional genetic dominance. While the correlations were similar in directionality for all groups, they varied considerably in magnitude, possibly because the groups differed substantially in environmental histories.     

Adolescent intelligence and socio-economic wealth independently predict adult marital and reproductive behavior

Counter-intuitively, sociobiological and evolutionary theories predict a negative relationship between g and reproduction when applied to modern humans. Although existing research has documented this dysgenic trend, the association between g and socio-economic factors presents a confound that has not systematically been addressed in prior research. Based on a sample of 325,252 individuals drawn from the nationally representative Project Talent database, we examined the unique effects of g and socio-economic wealth, assessed in adolescence, on marital and reproductive behavior over the next 11 years. Results show that both g and socio-economic wealth have unique, independent negative effects on marital and reproductive behavior such that individuals of higher intelligence and higher wealth delay marriage and reproductive longer than those of lower intelligence and wealth. The effect of g was slightly stronger than that of wealth, though for both variables much of their influence was mediated by educational attainment. Consistent with sociobiological theory, these dysgenic effects were stronger among females than males.     

Finding the g-factor in brain structure using the method of correlated vectors

It is unclear whether brain mechanisms underlying human intelligence are distributed throughout the brain or mainly concentrated in the frontal lobes. Data are inconsistent possibly due, at least in part, to the different ways the construct of intelligence is measured. Here we apply the method of correlated vectors to determine how the general factor of intelligence (g) is related to regional gray matter and white matter volumes. This is a re-analysis of an earlier study showing regional gray matter and white matter volume is correlated to Full Scale IQ (FSIQ). However, it is well-known that FSIQ taps several cognitive abilities and skills in addition to g. The results now show that the g factor accounts for several but not all FSIQ/gray matter correlations distributed throughout the brain and these areas may differ for young and older adults.     

Intelligence and semen quality are positively correlated

Human cognitive abilities inter-correlate to form a positive matrix, from which a large first factor, called ‘Spearman's g’ or general intelligence, can be extracted. General intelligence itself is correlated with many important health outcomes including cardio-vascular function and longevity. However, the important evolutionary question of whether intelligence is a fitness-related trait has not been tested directly, let alone answered. If the correlations among cognitive abilities are part of a larger matrix of positive associations among fitness-related traits, then intelligence ought to correlate with seemingly unrelated traits that affect fitness—such as semen quality. We found significant positive correlations between intelligence and 3 key indices of semen quality: log sperm concentration (r = .15, p = .002), log sperm count (r = .19, p < .001), and sperm motility (r = .14, p = .002) in a large sample of US Army Veterans. None was mediated by age, body mass index, days of sexual abstinence, service in Vietnam, or use of alcohol, tobacco, marijuana, or hard drugs. These results suggest that a phenotype-wide fitness factor may contribute to the association between intelligence and health. Clarifying whether a fitness factor exists is important theoretically for understanding the genomic architecture of fitness-related traits, and practically for understanding patterns of human physical and psychological health.     

Associations between cortical thickness and general intelligence in children,adolescents and young adults

Neuroimaging research indicates that human intellectual ability is related to brain structure including the thickness of the cerebral cortex. Most studies indicate that general intelligence is positively associated with cortical thickness in areas of association cortex distributed throughout both brain hemispheres. In this study, we performed a cortical thickness mapping analysis on data from 182 healthy typically developing males and females ages 9 to 24 years to identify correlates of general intelligence (g) scores. To determine if these correlates also mediate associations of specific cognitive abilities with cortical thickness, we regressed specific cognitive test scores on g scores and analyzed the residuals with respect to cortical thickness. The effect of age on the association between cortical thickness and intelligence was examined. We found a widely distributed pattern of positive associations between cortical thickness and g scores, as derived from the first unrotated principal factor of a factor analysis of Wechsler Abbreviated Scale of Intelligence (WASI) subtest scores. After WASI specific cognitive subtest scores were regressed on g factor scores, the residual score variances did not correlate significantly with cortical thickness in the full sample with age covaried. When participants were grouped at the age median, significant positive associations of cortical thickness were obtained in the older group for g-residualized scores on Block Design (a measure of visual-motor integrative processing) while significant negative associations of cortical thickness were observed in the younger group for g-residualized Vocabulary scores. These results regarding correlates of general intelligence are concordant with the existing literature, while the findings from younger versus older subgroups have implications for future research on brain structural correlates of specific cognitive abilities, as well as the cognitive domain specificity of behavioral performance correlates of normative gray matter thinning during adolescence.     

Formal reasoning in late adulthood: The role of semantic content and metacognitive strategy

Two experiments explored the availability of deductive or formal reasoning in late adulthood. In Experiment 1, fifty young (M=19.0 years) and 50 elderly adults (M=81.0 years) were assessed using adaptations of Wason's selection task and rated task content for familiarity, affect, and agreement. In Experiment 2, 100 young (M=21.0 years) and 100 elderly adults (M=81.0 years) were similarly assessed, with half of the subjects in each age group receiving a metacognitive strategy to facilitate reasoning. Results from Experiment 1 indicated equivalent reasoning among the groups on problems employed in earlier developmental research. In contrast, problems constructed to entail affect resulted in poorer performance by older adults. In Experiment 2, both young and older adults who used the metacognitive strategy reasoned equally acrossall problems. In both experiments, familiarity and agreement did not play a role in deductive reasoning performance, but affect seemed to be an interfering factor. Results are discussed in terms of competence-procedure and stability-decrement models of adult cognitive development.     

Epistemic closure and commutative, nonassociative residuated structures

K-axiom-based epistemic closure for explicit knowledge is rejected for even the most trivial cases of deductive inferential reasoning on account of the fact that the closure axiom does not extend beyond a raw consequence relation. The recognition that deductive inference concerns interaction as much as it concerns consequence allows for perspectives from logics of multi-agent information flow to be refocused onto mono-agent deductive reasoning. Instead of modeling the information flow between different agents in a communicative or announcement setting, we model the information flow between different states of a single agent as that agent reasons deductively. The resource management of the database of agent states for the deductive reasoning fragment in question is covered by the residuated structure that encodes the nonassociative Lambek Calculus with permutation, bottom, and identity: NLP ₀₁ .     

Effects of inbreeding on mental-ability factors

The differential effects of inbreeding on 11 subtests of the WISC, in a Japanese (Hiroshima) population, are related to the factor structure of the tests. The degree of inbreeding depression on mental abilities is most strongly correlated with the subtests' loadings on the General factor, g, which is common to all of the subtests. Loadings on the Verbal factor are also positively correlated with inbreeding depression. The (non-verbal) Performance factor, however, is slightly enhanced by inbreeding. One possible inference from these findings is that at least the General factor shows genetic dominance, which is theoretically consistent with natural selection for g in the course of human evolution. It is also noted that the factor structure of the WISC in the Japanese population is highly similar to that of the U.S. standardization sample.     

Relations between mental performance and reaction time: New aspects of an old problem

The relation between simple and complex reaction time and psychometrically determined mental performance was reexamined with 486 subjects of above-average intelligence. Various standardized tests measuring aspects of cognitive ability, memory and ability to concentrate were used. Simple and complex reaction times were measured using the Klebelsberg modification of the Mierke apparatus. Correlations between complex reaction time and mental performance as observed by other investigators were mostly confirmed. We found, however, the strongest and most consistent correlations with tests measuring short-term memory; ability to concentrate and spatial ability. On the other hand, tests known and shown again in this paper to load highly on Spearman's general factor g, such as verbal abilities; combinatoric thinking; abstraction; or calculation gave only trivial, and, in most cases, nonsignificant correlations with complex reaction time. We even observed a negative (though, for our data, not significant) correlation between g-loadings of subtests and their correlations with complex reaction time for the only complete standardized intelligence test used in this study, the “Intelligenz-Strukturtest (Amthauer).” Therefore, this study does not support the hypothesis that fast processing of complex information as measured by complex reaction time is the decisive component of the general factor of intelligence g.     

A unifying model for the structure of intellectual abilities

Models of the structure of cognitive abilities suggested by Spearman, Thurstone, Guilford, Vernon and Cattell-Horn are reviewed. It is noted that some of the models include a general intellectual factor (g) while others do not. It is also noted that some models are nonhierarchical, while in others more narrow abilities are subsumed under broader abilities in a hierarchical pattern. An empirical study in which a test battery of 16 tests was administered to some 1000 subjects in the 6th grade is reported. Using the LISREL technique to test different models, good support is obtained for oblique primary factors in the Thurstone tradition as well as for the second-order factors fluid intelligence, crystallized intelligence, and general visualization hypothesized by Cattell and Horn. It is also found, however, that the second-order factor of fluid intelligence i is identical with a third-order g-factor. On the basis of these results a three-level model (the HILI-model) is suggested, with the g-factor at the top, two broad factors reflecting the ability to deal with verbal and figural information, respectively, at the second-order level, and the primary factors in the Thurstone and Guilford tradition at the lowest level. It is argued that most previously suggested models are special cases of the HILI-model.     

The structure of working memory and how it relates to intelligence in children

This study explored the structure of working memory, and its relationship with intelligence in 176 typically-developing children in the 4th and 5th grades at school. Different measures of working memory (WM), and intelligence (g) were administered. Confirmatory factor analyses showed that WM involves an attentional control system and storage aspects that rely on domain-specific verbal (STM-V) and visuospatial (STM-VS) resources. The structural equation models showed that WM predicts a large portion (66%) of the variance in g, confirming that the two constructs are separable but closely related in young children. Findings also showed that only WM and STM-VS are significantly related to g, while the contribution of STM-V is moderate. Theoretical implications for the relationship between WM and g are discussed.     

“如果P,那么Q,……?”─—儿童充分条件假言演绎推理能力发展初探

以日常生活事件为内容的三套测验题探查了9－15岁儿童充分条件假言推理能力的发展。研究发现被试有关能力的发展可以区分出三种不同水平；儿童对充分条件假言推理规则的掌握没有固定的难易顺序，这取决于课题任务的性质和主体思维发展水平。研究还探查了发展的个体内部差异和个体之间的差异以及影响差异的各种内外因素。