Individual Differences In General Intelligence Research Articles

Cognitive reserve protects language functions in patients with brain tumours

Cognitive reserve (CR) theory suggests that individual differences in general intelligence (IQ), occupational attainment or participation in leisure/recreational activities protect against cognitive decline. However the relationship between CR and cognitive functioning in patients with brain tumours has been very rarely investigated in past research. The present study systematically assesses whether CR concept can also be applied to cognitive functions of neurosurgical patients affected by brain tumours. We investigated the role of different CR proxies (education level, premorbid IQ, current IQ, working and leisure activity) in protecting language against brain tumours and surgery effects, considering interactions with demographic (sex/age), anatomical (hemisphere/lobe location of lesion) and clinical/biological variables (tumour type: High/Low Grade Glioma or Meningioma; lesion volume; lesion aggressiveness). One-hundred patients undergoing neuropsychological assessment before and immediately after surgery participated. A “Language Score” summarizing performance on all language tests was derived with Principal Component Analysis. Data were then analyzed with Multiple Regression and Classification and Regression Tree analyses to investigate possible relationships between predictors (CR proxies and clinical variables) and Language Score. We found that premorbid IQ was the best predictor of pre-operatory language integrity, above and beyond all clinical variables considered, also moderating lesion volume effects. Moreover, patients with lower pre-operatory language integrity and low-to-moderately aggressive tumours showed a mitigating effect of current IQ over surgery consequences. Results thus suggest that different CR proxies play a role in moderating cognitive decline following brain tumours and surgery.

Neuroenergetics and "General Intelligence": A Systems Biology Perspective.

David C. Geary proposed the efficiency of mitochondrial processes, especially the production of energy, as the most fundamental biological mechanism contributing to individual differences in general intelligence (g). While the efficiency of mitochondrial functioning is undoubtedly an important and highly interesting factor, I outline several reasons why other main factors of neuroenergetics should not be neglected and why a systems biology perspective should be adopted. There are many advantages for research on intelligence to focus on individual differences in the capability of the overall brain metabolism system to produce the energy currency adenosine triphosphate (ATP): higher predictive strength than single mechanisms, diverse possibilities for experimental manipulation, measurement with existing techniques and answers to unresolved questions because of multiple realizability. Many of these aspects are especially important for research on developmental processes and the building and refining of brain networks for adaptation. Focusing too much on single parts of the system, like the efficiency of mitochondrial functioning, carries the danger of missing important information about the role of neuroenergetics in intelligence and valuable research opportunities.

Mitochondria as the Linchpin of General Intelligence and the Link between g, Health, and Aging.

In a recent theoretical article, I proposed that the efficiency of mitochondrial functioning is the most fundamental biological mechanism contributing to individual differences in general intelligence (g; Geary, 2018). The hypothesis accommodates other contributing mechanisms at higher levels of analysis (e.g., brain networks), and is attractive because mitochondrial energy production undergirds the developmental, maintenance, and expression of these other mechanisms and provides a means to link individual differences in g to individual differences in health and successful aging in adulthood. I provide a brief summation here and a few clarifications to the original article.

Predicting piano skill acquisition in beginners: The role of general intelligence, music aptitude, and mindset

This study was designed to investigate sources of individual differences in musical skill acquisition. We had 171 undergraduates with little or no piano-playing experience attempt to learn a piece of piano music with the aid of a video-guide, and then, following practice with the guide, attempt to perform the piece from memory. A panel of musicians evaluated the performances based on their melodic and rhythmic accuracy. Participants also completed tests of working memory capacity, fluid intelligence, crystallized intelligence, processing speed, and two tests of music aptitude (the Swedish Music Discrimination Test and the Advanced Measures of Music Audiation). Measures of general intelligence and music aptitude correlated significantly with skill acquisition, but mindset did not. Structural equation modeling revealed that general intelligence, music aptitude, and mindset together accounted for 22.4% of the variance in skill acquisition. However, only general intelligence contributed significantly to the model (β = 0.44, p < .001). The contributions of music aptitude (β = 0.08, p = .39) and mindset (β = −0.06, p = .50) were non-significant after accounting for general intelligence. We also found that openness to experience did not significantly predict skill acquisition or music aptitude. Overall, the results suggest that after accounting for individual differences in general intelligence, music aptitude and mindset do not predict piano skill acquisition in beginners.

Faster, but not smarter: An experimental analysis of the relationship between mental speed and mental abilities

Individual differences in the speed of information processing may contribute to individual differences in general intelligence by enhancing the efficiency of information processing. So far, this hypothesis is based on correlational data, and thus a causal relationship between mental speed and mental abilities has not yet been established. In the present study, we used transdermal nicotine administration in a double-blind design to increase the speed of information processing and tested whether this increase in information processing speed affected performance in intelligence tests. While nicotine administration decreased both reaction times and P3 latencies in the Sternberg memory scanning task, there was no effect of nicotine on intelligence test performance. These results contradict theories proposing that a greater speed of information processing causes greater intelligence. Instead, they suggest that structural properties of the brain may affect both the speed of information processing and general intelligence and may thus give rise to the well-established association between mental speed and mental abilities.

Is general intelligence little more than the speed of higher-order processing?

Individual differences in the speed of information processing have been hypothesized to give rise to individual differences in general intelligence. Consistent with this hypothesis, reaction times (RTs) and latencies of event-related potential have been shown to be moderately associated with intelligence. These associations have been explained either in terms of individual differences in some brain-wide property such as myelination, the speed of neural oscillations, or white-matter tract integrity, or in terms of individual differences in specific processes such as the signal-to-noise ratio in evidence accumulation, executive control, or the cholinergic system. Here we show in a sample of 122 participants, who completed a battery of RT tasks at 2 laboratory sessions while an EEG was recorded, that more intelligent individuals have a higher speed of higher-order information processing that explains about 80% of the variance in general intelligence. Our results do not support the notion that individuals with higher levels of general intelligence show advantages in some brain-wide property. Instead, they suggest that more intelligent individuals benefit from a more efficient transmission of information from frontal attention and working memory processes to temporal-parietal processes of memory storage. (PsycINFO Database Record

Can we reliably measure the general factor of intelligence (g) through commercial video games? Yes, we can!

Here we show, for the very first time, that commercial video games can be used to reliably measure individual differences in general intelligence (g). One hundred and eighty eight university undergraduates took part in the study. They played twelve video games under strict supervision in the laboratory and completed eleven intelligence tests. Several factor models were tested for answering the question of whether or not video games and intelligence tests do measure the same underlying high-order latent factor. The final model revealed a very high relationship between the high-order latent factors representing video game and intelligence performance (r=.93). General performance scores derived from video games and intelligence tests showed a correlation value of .963 (R2adjusted). Therefore, performance on some video games captures a latent factor common to the variance shared by cognitive performance assessed by standard ability tests.

Where smart brains are different: A quantitative meta-analysis of functional and structural brain imaging studies on intelligence

Individual differences in general intelligence have been associated with differences in brain structure and function. The currently most popular theory of the neural bases of intelligence – the Parieto-Frontal Integration Theory of Intelligence (P-FIT) – describes a network of frontal and parietal brain regions as the main neural basis of intelligence. Here, we put the theory to an empirical test by conducting voxel-based quantitative meta-analyses of 12 structural and 16 functional human brain imaging studies, testing for statistically significant spatial convergence across studies. We focused our analyses on studies reporting associations between individual differences in intelligence (as assessed by established tests of psychometric intelligence) and either (a) brain activation during a cognitive task (functional meta-analysis) or (b) amount of grey matter as assessed by voxel-based morphometry (structural meta-analysis). The functional meta-analysis resulted in eight clusters distributed across both hemispheres, located in lateral frontal, medial frontal, parietal, and temporal cortices. The structural meta-analysis of VBM studies resulted in 12 clusters distributed in lateral and medial frontal, temporal, and occipital cortices, as well as in subcortical structures. Results of the functional and structural meta-analyses did not show any overlap — although both independently showed good match with the P-FIT. Based on the meta-analyses, we present an updated model for the brain bases of intelligence that extends previous models in also considering the posterior cingulate cortex and subcortical structures as relevant for intelligence, and in differentiating between positive and negative associations of intelligence and brain activation. From a critical review of original studies and methods, we derive important suggestions for future research on brain correlates of intelligence.

Early event-related brain potentials and hemispheric asymmetries reveal mind-wandering while reading and predict comprehension

The electroencephalogram (EEG) of mind-wandering (MW) was examined in event-related potentials (ERPs) and pre-stimulus alpha (8–12Hz), over lateral-posterior sites of left and right brain hemispheres, while individuals read text passages. After controlling for individual differences in general intelligence (g), P1-asymmetry was greater (right-minus- left) and N1 amplitudes were more negative, when individuals were not MW (i.e., they were reading attentively). Approximately 82% of variance in reading comprehension was accounted for by the predictors: g, pre-stimulus alpha, left- and right-hemisphere P1, and left-hemisphere N1 (when individuals were not MW). Together, individual differences in MW-sensitive ERPs uniquely accounted for approximately 38% of the variance in reading comprehension, over and above prediction by g and pre-stimulus alpha. The within-person effect of MW on P1-asymmetry was estimated to account for an additional 4.6% of criterion variance. Implications for EEG/ERP research into attention, language processing, hemispheric asymmetries, and individual differences are discussed.

Medial frontal white and gray matter contributions to general intelligence.

The medial orbitofrontal cortex (mOFC) and rostral anterior cingulate cortex (rACC) are part of a wider neural network that plays an important role in general intelligence and executive function. We used structural brain imaging to quantify magnetic resonance gray matter volume and diffusion tensor white matter integrity of the mOFC-rACC network in 26 healthy participants who also completed neuropsychological tests of intellectual abilities and executive function. Stochastic tractography, the most effective Diffusion Tensor Imaging method for examining white matter connections between adjacent gray matter regions, was employed to assess the integrity of mOFC-rACC pathways. Fractional anisotropy (FA), which reflects the integrity of white matter connections, was calculated. Results indicated that higher intelligence correlated with greater gray matter volumes for both mOFC and rACC, as well as with increased FA for left posterior mOFC-rACC connectivity. Hierarchical regression analyses revealed that DTI-derived FA of left posterior mOFC-rACC uniquely accounted for 29%–34% of the variance in IQ, in comparison to 11%–16% uniquely explained by gray matter volume of the left rACC. Together, left rACC gray matter volume and white matter connectivity between left posterior mOFC and rACC accounted for up to 50% of the variance in general intelligence. This study is to our knowledge the first to examine white matter connectivity between OFC and ACC, two gray matter regions of interests that are very close in physical proximity, and underscores the important independent contributions of variations in rACC gray matter volume and mOFC-rACC white matter connectivity to individual differences in general intelligence.

The role of placekeeping ability in fluid intelligence.

The question of what underlies individual differences in general intelligence has never been satisfactorily answered. The purpose of this research was to investigate the role of an executive function that we term placekeeping ability-the ability to perform the steps of a complex task in a prescribed order without skipping or repeating steps. Participants completed a newly developed test of placekeeping ability, called the UNRAVEL task. The measure of placekeeping ability from this task (error rate) predicted a measure of fluid intelligence (Raven's Advanced Progressive Matrices score), above and beyond measures of working memory capacity, task switching, and multitasking. An existing model of Raven's performance suggests that placekeeping ability supports the systematic exploration of hypotheses under problem-solving conditions.

Placing inspection time, reaction time, and perceptual speed in the broader context of cognitive ability: The VPR model in the Lothian Birth Cohort 1936

The idea that information processing speed is related to cognitive ability has a long history. Much evidence has been amassed in its support, with respect to both individual differences in general intelligence and developmental trajectories. Two so-called elementary cognitive tasks, reaction time and inspection time, have been used to compile this evidence, but most studies have used either one or the other. Relations between speed and fluid intelligence have tended to be stronger than those between speed and crystallized intelligence, but studies testing this have confounded verbal abilities with crystallized intelligence and spatial/perceptual abilities with fluid intelligence. Questions have also been raised regarding whether speed contributes directly to general intelligence or to more specific cognitive abilities to which general intelligence also contributes. We used 18 ability and speed measures in the Lothian Birth Cohort 1936, assessed at approximately age 70, to construct alternative versions of the Verbal–Perceptual–Image Rotation (Johnson & Bouchard, 2005a) model of cognitive ability to test different hypotheses regarding these issues. Though differences in the extents to which our models fit the data were relatively small, they suggested that reaction and inspection time tasks were comparable indicators of information processing speed with respect to general intelligence, that verbal and spatial abilities were similarly related to information processing speed, and that spatial, verbal, and perceptual speed abilities were more directly related to information processing speed than was general intelligence. We discuss the theoretical implications of these results.

An integrated perspective on the relation between response speed and intelligence

Research in the field of mental chronometry and individual differences has revealed several robust regularities (Jensen, 2006). These include right-skewed response time (RT) distributions, the worst performance rule, correlations with general intelligence (g) that are more pronounced for RT standard deviations (RTSD) than they are for RT means (RTm), an almost perfect linear relation between individual differences in RTSD and RTm, linear Brinley plots, and stronger correlations between g and inspection time (IT) than between g and RTm. Here we show how all these regularities are manifestations of a single underlying relationship, when viewed through the lens of Ratcliff’s diffusion model (Ratcliff, 1978; Ratcliff, Schmiedek, & McKoon, 2008). The single underlying relationship is between individual differences in general intelligence and individual differences in “drift rate”, which is just the speed of information processing in Ratcliff’s model. We also test and confirm a strong prediction of the diffusion model, namely that the worst performance rule generalizes to phenomena outside of the field of intelligence. Our approach provides an integrative perspective on intelligence findings.

Evolutionary psychology and intelligence research cannot be integrated the way Kanazawa (2010) suggested.

Evolutionary psychology and intelligence research cannot be integrated the way Kanazawa (2010) suggested.

Individual differences in general intelligence correlate with brain function during nonreasoning tasks

Brain imaging can help identify the functional neuroanatomy of general intelligence (i.e., “ g”) and indicate how brain areas salient to g relate to information processing. An important question is whether individual differences in g among subjects are related to brain function even when nonreasoning tasks are studied. If so, this would imply that individuals with high g scores may process information differently even when no reasoning or problem solving is required. To further investigate this, we administered the Raven's Advanced Progressive Matrices (RAPM) test, a strong correlate of g, to 22 normal subjects and then measured cerebral glucose metabolic activity with PET while the subjects viewed videos on two occasions, tasks with no inherent reasoning or problem solving. Individual RAPM scores were correlated with regional brain activity using statistical parametric mapping (SPM99) conjunction analysis to combine both video conditions. Results showed greater activation in specific posterior brain areas (left BA37/19) in high RAPM scorers ( P=.02, corrected for multiple comparisons). Subsequent analyses revealed a high/low RAPM group difference in functional connectivity between left BA37/19 activity and the left anterior cingulate/medial frontal gyrus. These data provide evidence that individual differences in intelligence correlate to brain function even when the brain is engaged in nonreasoning tasks and suggest that high and low g subjects may preferentially activate different neural circuits, especially nonfrontal areas involved in information processing.

Quantitative trait locus analysis of contextual fear conditioning in mice.

Family, twin and adoption studies provide evidence for a substantial genetic component underlying individual differences in general intelligence, specific cognitive abilities and susceptibility to psychopathologies related to fear-inducing events. Contextual fear conditioning, which is highly conserved across species, can serve as a model for elucidating genes that regulate individual differences in learning and emotion. In fear conditioning, an initially neutral stimulus, such as a tone or a particular environment (context), elicits a fear response after it has been paired with an aversive stimulus, such as shock. Two neural circuits have been implicated in fear conditioning. The fear component is regulated by amygdaloid pathways, while the contextual component is, at least in part, dependent on the hippocampus. C57BL/6J (B6) and DBA/2J (D2) mice differ in several types of complex learning. including contextual fear conditioning. A quantitative trait locus (QTL) analysis of contextual fear conditioning was performed in a B6/D2 F2 intercross population. Two QTLs for contextual conditioning (lod score > 4.3) were identified on chromosomes 10 and 16. QTLs for conditioning to the auditory cue (lod score > 4.3) were localized to chromosomes 1 and 10. Suggestive QTLs (lod score = 2.8-4.1) for contextual conditioning were detected on chromosomes 1, 2 and 3.

From memory span and mental speed toward the quantum mechanics of intelligence

Multiplying memory span by mental speed, we obtain the entropy of short-term memory capacity, which is rate-limiting for performance in intelligence tests. Information entropy can also be calculated by using the entropy formula for quantum particles (bosons), in which case memory span becomes the quantum number n. The first harmonic of the cavity resonator brain is the eigenfrequency π; and entropy can be expressed as n 2 π ( n = 1,2,…,9). The fact that high IQ subjects exhibit a greater complexity of EEG follows from the quantum number increase for the wave function with the result of higher brain power for Fourier transformation of information. Such individual differences in general intelligence are caused by differences in brain energy metabolism. Consequently, cerebral glucose metabolism rate and IQ have been found highly correlated. The responsible regulatory mechanism of oscillatory glycolysis is redox control by thiol disulphide exchange in which the genetic polymorphism of glutathione peroxidase plays a key role.

Stability and change in adult intelligence: 1. Analysis of longitudinal covariance structures.

We address two questions of central interest in adult intellectual development: the equivalence of psychometric tests' measurement properties at different ages, and the stability of individual differences in intelligence over time. We performed a series of longitudinal factor analyses using the LISREL program to model longitudinal data from Schaie's Seattle Longitudinal Study. The results indicate complete invariance in the loadings of five subtests of Thurstone's Primary Mental Abilities battery on a general intelligence factor. Individual differences in general intelligence were highly stable over 14-year epochs, with standardized factor correlations averaging about .9 between adjacent 7-year testing intervals. These results indicate that most individuals in this relatively select longitudinal sample maintained their relative ordering in intelligence.

HEREDITY AND INTELLIGENCE: A REPLY TO CRITICISMS

SummaryAn attempt is made to remove current misconceptions about the way in which individual differences in general intelligence appear to be inherited. Further support for a multifactorial form of the Mendelian theory is found in an examination (a) of the commoner objections, both methodological and statistical, and (b) of the chief alternative hypotheses, viz., (i) the theory of blending inheritance and (ii) the theory of exclusively or predominantly environmental determination.