Chinese sex differences in intelligence: Some new evidence

Sex differences on the WISC-R in Chinese children were examined in a sample of 788 aged 12 years. Boys obtained a higher mean full scale IQ than girls of 3.75 IQ points, a higher performance IQ of 4.20 IQ points, and a higher verbal IQ of 2.40 IQ points. Boys obtained significantly higher means on the information, picture arrangement, picture completion, block design, and object assembly subtests, while girls obtained a significantly higher mean on coding. The results were in general similar to the sex differences in the United States standardisation sample of the WISC-R. Boys showed greater variability than girls.     

Independent effects of personality and sex on self-estimated intelligence: evidence from Austria

The effects of sex and personality traits on self-estimates of intelligence were examined in a sample of 302 Austrian adults (143 men, 159 women). Confirming previous research, men had higher self-estimates of logical and spatial abilities than did women, and these differences were partly explained in terms of women's higher Neuroticism scores. Neuroticism (negatively) and Openness (positively) accounted significantly for variances in self-estimates of spatial and logical intelligence. However, sex had stronger direct and indirect effects on self-estimates of intelligence. Sex and personality effects appear to be largely independent. Thus, being male, emotionally stable, and open to new experiences is likely to result in higher self-estimates of spatial and logical abilities.     

Age differences in fluid intelligence: contributions of general slowing and frontal decline

The current study examined the contributions of general slowing and frontal decline to age differences in fluid intelligence. Participants aged 20-89 years completed Block Design, Matrix Reasoning, simple reaction time, choice reaction time, Wisconsin Card Sorting, and Tower of London tasks. Age-related declines in fluid intelligence, speed of processing, and frontal function were observed. Hierarchical regression analyses showed that the processing speed and frontal function measures accounted for significant variance in fluid intelligence performance, but there was also a residual effect of age after controlling for each variable individually as well as both variables. An additional analysis showed that the variance in fluid intelligence that was attributable to processing speed was not fully shared with the variance attributable to frontal function. These findings suggest that the age-related decline in fluid intelligence is due to general slowing and frontal decline, as well as other unidentified factors.     

Cerebral lateralization and general intelligence: gender differences in a transcranial Doppler study

The present study evaluated cerebral lateralization during Raven's progressive matrices (RPM) paradigm in female and male subjects. Bilateral simultaneous transcranial Doppler (TCD) ultrasound was used to measure mean blood flow velocities (MBFV) in the right and left middle cerebral arteries (MCAs) in 24 (15 females and 9 males) right-handed normal subjects. The female subjects used a left hemisphere strategy, while males used a right hemisphere strategy to successfully solve RPM tasks. This implies that general intelligence is associated with neural systems within one hemisphere that are accessible to a variety of cognitive processes.     

Sex differences in brain activity related to general and emotional intelligence

The study investigated gender differences in resting EEG (in three individually determined narrow alpha frequency bands) related to the level of general and emotional intelligence. Brain activity of males decreased with the level of general intelligence, whereas an opposite pattern of brain activity was observed in females. This difference was most pronounced in the upper-alpha band which is related to semantic memory processes. It was further found that highly intelligent males displayed greater decoupling of frontal brain areas, whereas highly intelligent females showed more coupling between frontal and parietal/occipital brain areas. Similar, but less significant differences were observed for the two area scores of strategic and experiential emotional intelligence. It appears that males and females have different resting EEG correlates of IQ.     

Behavioural evidence for sex differences in the overlap between subtraction and multiplication

The present study aims to identify factors that may influence the dissociability of number magnitude processing and arithmetic fact retrieval at the behavioural level. To that end, we assessed both subtraction and multiplication performance in a within-subject approach and evaluated the interdependence of unit-decade integration measures on the one hand as well as sex differences in the interdependence of performance measures on the other hand. We found that subtraction items requiring borrowing (e.g. 53–29 = 24, 3 < 9) are more error prone than subtraction items not requiring borrowing (e.g. 59–23 = 34, 9 > 3), thereby demonstrating a borrowing effect, which has been suggested as a measure of unit-decade integration in subtraction. Furthermore, we observed that multiplication items with decade-consistent distractors (e.g. 6 × 4 = 28 instead of 24) are more error prone that multiplication items with decade-inconsistent distractors (e.g. 6 × 4 = 30 instead of 24), thereby demonstrating a decade-consistency effect, which has been suggested as a measure of unit-decade integration in simple multiplication. However, the borrowing effect in subtraction was not correlated with the effect of decade consistency in simple multiplication in either men or women. This indicates that unit-decade integration arises from different systems in subtraction and multiplication. Nevertheless, men outperformed women not only in subtraction, but also in multiplication. Furthermore, subtraction and multiplication performance on correct solution probes were correlated in women, but unrelated in men. Thus, the view of differential systems for number magnitude processing and arithmetic fact retrieval may not be universal across sexes.     

Decomposing self‐estimates of intelligence: Structure and sex differences across 12 nations

This study examines the structure of self‐estimates of intelligence (SEI) across 12 nations (Australia, Austria, Brazil, France, Iran, Israel, Malaysia, South Africa, Spain, Turkey, UK and US). Participants rated themselves on general and specific abilities from three popular models of intelligence: Gardner's multiple intelligences, Sternberg's triarchic theory of intelligence, and Goleman's emotional intelligence. The results showed that (a) laypeople across nations have similar and invariant concepts of intelligence, (b) concepts of intelligence are cross‐culturally closely related to academic notions of intellectual ability and (c) sex differences in general and specific SEI favouring men are consistent across countries. Male hubris and female humility in SEI seem independent of sex differences in actual cognitive ability and national levels of masculinity‐femininity. Furthermore, international mean differences in general SEI could not be attributed to discrepancies in national intelligence quotient (IQ) levels or to cultural variations.     

Twin-singleton differences in intelligence: a meta-analysis

Since the emergence of twin studies in the 1920s, time and again the question of possible twin-singleton differences in intelligence has been posed. This study addressed the issue through a meta-analysis of published studies on this theme. Twins on the average seem to have lower IQs than singletons. The best estimate for this group difference is 4.2 IQ points (less than one-third of a standard deviation), with a great divide between study outcomes of less vs more recent birth cohorts (5.1 vs 0.5 IQ points, respectively). The evidence is based on studies from six countries (including population-based ones of entire birth cohorts), a massive database (comparisons of more than 30,000 twins with nearly 1.6 million singletons), a variety of intelligence tests, and birth cohorts spanning most of the 20th century, but, for the most part, on an age range limited to children and adolescents. The effect shows considerable between-study heterogeneity but appears robust (fail-safe N calculations), not due to influential individual studies (sensitivity analysis) or publication bias, was present since the very first published studies (cumulative meta-analysis), and appears generalizable across sex, zygosity, and other intelligence domains beyond the verbal. There are insufficient data as to whether the effect persists over the lifespan, exists as well within families, or has ceased in recent birth cohorts of highly developed countries (Denmark and The Netherlands). Likely causes of the effect appear to be prenatal and perinatal factors (reduced fetal growth and shorter gestation for twins).     

An evaluation of evidence for innate sex differences in linguistic ability

A female superiority in verbal ability is reported on many tests. It has been hypothesized that the female brain is more functionally symmetrical for language then the male, and that this is the cause of the alleged superiority. Recent research has suggested that factors other than sex are involved: handedness, age of maturity, and endocrine influences. It is not yet clear whether, despite its biological correlates, the female superiortiy is innate.     

Using a general model of personality to understand sex differences in the personality disorders

In the present study, a general model of personality was used to evaluate sex bias in the personality disorders (PD). This present study compared observed sex differences among the personality disorders (PD) with differences expected based on the Five Factor Model of personality functioning (FFM). Observed sex differences were obtained by metaanalyzing over 30 reports. Expected sex differences were computed using what is known about sex differences in the FFM traits and how these traits relate to the PDs. Agreement between observed and expected sex differences was quite good for eight of ten PDs. For histrionic PD, the obtained sex difference was larger than expected; for schizotypal personality disorder, an expected sex difference was not obtained. Implications of understanding sex differences in terms of the FFM are discussed and suggestions for future research are provided.     

New evidence for the prediction of intelligence from infancy

An assumption is made that tests of the infant's ability to recognize a previously seen target tap early cognitive processes similar to those processes employed to solve later tests of intelligence. The recognition memory abilities of normal infants have been found to be superior to those of infants considered to be at risk for later intellectual deficit. Evidence for the predictive validity of infant recognition memory tests emerges from longitudinal studies in which the relationship between the extent of infants' visual preferences for novel targets and later performance on standard tests of intelligence has been examined. Various theoretical and practical consequences flow from these initial discoveries of continuity in intelligent functioning from infancy to childhood.     

Sex differences in brain volume are related to specific skills, not to general intelligence

It has been proposed that males would show higher mean scores than females in general intelligence (g) because (1) men have, on average, larger brains than women, and (2) brain volume correlates with g. Here we report a failure to support the conclusion derived from these premises. High resolution MRIs were acquired in a sample of one hundred healthy young participants for estimating total, gray, and white matter volumes. Participants also completed an intelligence battery - comprising tests measuring abstract, verbal, and spatial abilities - that allowed the extraction of g scores. Results showed consistent relations between sex differences in brain volumes and non-g spatial and verbal skills but not for g.     

A longitudinal study of sex differences in intelligence at ages 7, 11 and 16 years

This paper presents the results of a longitudinal study of sex differences in intelligence as a test of Lynn’s (1994) hypothesis that from the age of 16 years males develop higher average intelligence than females. The results show that at the ages of 7 and 11 years girls have an IQ advantage of approximately 1 IQ point, but at the age of 16 years this changes in the same boys and girls to an IQ advantage of 1.8 IQ points for boys.     

Understanding the nature of the general factor of intelligence: the role of individual differences in neural plasticity as an explanatory mechanism

The nature of the general factor of intelligence, or g, is examined. This article begins by observing that the finding of a general factor of intelligence appears to be inconsistent with current findings in neuroscience and cognitive science, where specific connections are argued to be critical for different intellectual abilities and the brain is argued to develop these connections in response to environmental stimuli. However, it is then observed that if people differed in neural plasticity, or the ability to adapt their connections to the environment, then those highly developed in one intellectual ability would be highly developed in other intellectual abilities as well. Simulations are then used to confirm that such a pattern would be obtained. Such a model is also shown to account for many other findings in the field of intelligence that are currently unexplained. A critical period for intellectual development is then emphasized.     

Individual differences in intelligence: A reappraisal of the confluence model

The confluence model posits that an individual's intellectual development is a function of the intellectual environment he or she is exposed to in the home. Families with many children spaced close together are presumed to have intellectual environments inferior to those of families with few children spaced far apart. To date, the major support for the confluence model has come from analyses of the family size-birth order means of large aggregate data sets. Analyses of the individual scores of some of those same aggregate data sets, however, do not substantiate the confluence model. Explained variance for the aggregate (90%+) reduce to less than 3% in the individual analyses. A recommendation is made to shift the focus of the confluence model from family configuration variables to family interaction varibles utilizing longitudinal data from individuals.