Dispersion in Cognitive Ability as a Function of Age: A Longitudinal Study of an Elderly Community Sample

This longitudinal study investigated whether age is associated with increased dispersion among major domains of cognitive ability. Three samples were examined: the full sample of 760 elderly community dwellers aged 70 years and older who were tested in 1990; a subset of the original sample who died between testing occasions; and the sample of 426 who survived with full data sets in 1994 (followed up for a mean 3.5 years). Dispersion, as measured by the within-individual standard deviation of ability scores and by the within-individual deviations from crystallized intelligence for speed, memory and spatial functioning, was significantly correlated with age in all three samples at Wave 1 and at Wave 2 (for the longitudinal sample). The rate at which dispersion increased was not significantly correlated with age. In a more detailed analysis of the 426 survivors, dispersion as a function of age was similar for demented persons within this sample, those without dementia, those with poor and excellent educational levels, and those with a physical disability. Activities of daily living was a predictor of larger-than-average changes in dispersion – but not age, education, or activity. Greater dispersion was associated with faster deterioration in memory and speed performance. Contrary to some recent reports, there was evidence for greater within-individual variability among cognitive domains in older individuals.     

Criterion Validity of the Rorschach Developmental Index With Children

The Rorschach Developmental Index (DI) is a composite measure of psychological development. The aim of this study was to examine the criterion validity of the DI by investigating its relationship with age, nonverbal intelligence, and the impact of institutionalization in a sample of Brazilian children. The sample included 231 children, ages 7 to 11, who were either living with their families or in an institutionalized setting. The results indicated that the DI is strongly associated with nonverbal intelligence. Multiple regression analysis revealed that 71% of the variability in the DI was associated with nonverbal intelligence, whereas age explained only 2%. Moreover, the DI scores and nonverbal intelligence scores were significantly lower for children living in institutionalized settings. The DI appears to be effective in assessing various levels of psychological development, especially when expressed in cognitive ability. The DI was developed in the United States, and this study suggests that the DI can be adapted to diverse cultures, regions, or languages.     

Recycling,evolution and the structure of human personality

Lower childhood cognitive ability may be a risk factor for greater cognitive decline in late life and progression to dementia. To assess variation in age-related cognitive change, it is helpful to have valid measures of cognitive ability from early life. Here, we examine the relation between childhood intelligence and cognitive change in later life in two samples, one born in 1921 and the other in 1936. All participants completed the same test of mental ability (one of the Moray House Test series) at age about 11 years, and were re-examined on Raven’s Progressive Matrices at age 77 (1921-born) or age 64 (1936-born). Where possible, the 1921 sample was re-tested at the age of about 80 years old and the 1936 sample re-tested at about 66 years. After taking into account various covariates, including sex, education and occupation, childhood intelligence was a significant predictor of cognitive change in later life. Results were in the direction that participants with lower childhood mental ability experienced relatively greater cognitive decline, whereas those of higher childhood mental ability showed improved performance. This result suggests that higher premorbid cognitive ability is protective of decline in later life.     

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.     

Type 2 Diabetes Mellitus and Cognitive Performance in a Population-Based Sample of the Oldest Old: Impact of Comorbid Dementia

We examined the relationship between type 2 diabetes mellitus and cognitive function in a population-based sample of very old people. The sample comprised 338 persons, aged 80-93 years (mean age 83.5 years), of whom 70 persons had type 2 diabetes mellitus. Measures of cognitive functioning included tests of perceptual speed, visuo-spatial ability, inductive reasoning, short-term memory, semantic memory, episodic memory, and the Mini-Mental State Examination. Regression analyses showed that type 2 diabetes mellitus duration was related to test performance across all cognitive domains, with the exception of short-term memory, such that longer duration was associated with lower test performance. When cases with dementia were excluded from the sample, further analyses showed that diabetes duration was not associated with cognitive test performance. This indicates that diabetes is not related to lower cognitive function in the general population of non-demented old people. Diabetes, however, increases the risk for cerebrovascular incidents, like stroke, that may contribute to vascular dementia.     

Intelligence Level and the Allocation of Resources for Creative Tasks: A Pupillometry Study

This pupillometry study examined the relationship between intelligence and creative cognition from the resource allocation perspective. It was hypothesized that, during a creative metaphor task, individuals with higher intelligence scores would have different resource allocation patterns than individuals with lower intelligence scores. The study also examined the influence of intelligence in language and visuo-spatial domains on the resource allocation mechanism of verbal and visual creativity. The results suggested that individuals with higher intelligence scores allocated more cognitive resources for creative tasks than those with lower intelligence scores but not for non-creative tasks. The findings of this study support the view that creativity requires allocation of several cognitive faculties and may share underlying cognitive and neural mechanisms with intelligence. Domain-specific intelligence did not seem to play a significant role in the same domain, as individuals with higher scores in both domains showed similar resource allocation patterns. However, individuals with higher intelligence scores in the visuo-spatial domain generated more creative metaphorical interpretations in both verbal and visual creative metaphor tasks suggesting its importance in creative cognition.     

Predicting school achievement from cognitive and non-cognitive variables in a Chinese sample of elementary school children

The present study had two aims: First, to investigate the joint and specific roles of working memory (WM) and intelligence as predictors of school achievement. And second, to replicate and extend earlier findings (Spinath, Spinath, Harlaar, & Plomin, 2006) on the incremental validity of non-cognitive over cognitive abilities in the prediction of school achievement. The present sample consisted of N = 179 Chinese primary school children in the fourth grade. All measures including working memory (WM), intelligence and motivational items were assessed in class. Teachers provided test scores for the domains of Chinese and Math. We found that WM was a good predictor of school achievement and comparable in predictive power to intelligence. Together, cognitive ability including both WM and intelligence explained 17.8% and 36.4% of the variance in children's Chinese and Math scores, respectively. The relative importance of WM and intelligence varied with school domains with greater predictive power of WM for Math while intelligence explained a greater proportion of the variance in Chinese although the magnitude of this difference was only moderate. Domain-specific motivational constructs contributed only marginally to the prediction of school achievement for both Chinese and Math.     

There are stable individual differences in performance variability, both from moment to moment and from day to day

Individual differences in decision speed have been regarded as direct reflections of a "primitive" functional neurophysiological characteristic, which affects performance on all cognitive tasks and so may be regarded as the "biological basis of intelligence", or of age-related changes in mental abilities. More detailed analyses show that variability within an experimental session (WSV) is a stable individual difference characteristic and that mean choice reaction times (CRTs) are gross summary statistics that reflect variability, rather than maximum speed of performance. A total of 98 people aged from 60 to 80 years completed 36 weekly sessions on six different letter categorization tasks. After effects of practice and of circadian variability had been eliminated, individuals with lower scores on the Cattell Culture Fair intelligence test had slower CRTs and greater WSV on all tasks. A simulation study showed that the greater WSVs of low Cattell scorers led directly to the significantly greater variability of their mean CRTs from session to session. However because CRTs on tasks co-varied from session to session it was apparent that, besides being affected by WSV, individuals' between-session variabilities (BSVs) also vary because of state changes that affect their performance from day to day. It seems that both variability in performance from trial to trial during a session and variability in average performance from day to day are correlated, stable, individual difference characteristics that vary inversely with intelligence test performance. Methodological consequences of these results for interpretations of age-related cognitive changes, for variability between as well as within individuals, for individual differences in decision speed, and for circadian variability in performance are discussed.     

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.     

Analysis of WAIS-IV index score scatter using significant deviation from the mean index score

The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) does not include verbal IQ and performance IQ scores, as provided in previous editions of the scale; rather, this edition provides comparisons among four index scores, allowing analysis of an individual's WAIS-IV performance in more discrete domains of cognitive ability. To supplement the pairwise index score comparisons included in the WAIS-IV manuals, this article describes the use of the mean of the four index scores (the average index score) as a baseline for analyzing index score variability and as a method for identifying strengths and weaknesses within an individual's index score pattern. Davis's formula was used to calculate critical values for the identification of index scores with a statistically significant difference from the average index score. Subsequent analysis of the WAIS-IV normative sample indicates that variability in performance at the index score level is not uncommon in the general population. More than 70% of individuals in the normative sample have at least one index score that differs significantly from their mean index score. This variability in index score performance appears to have little relationship to age or gender, but it is strongly related to the full-scale IQ.     

Ability Emotional Intelligence Predicts Quality of Life beyond Personality,Affectivity, and Cognitive Intelligence

The current study explored the incremental validity of the ability emotional intelligence test to predict suicidal ideation (a subjective indicator of Quality of Life) beyond the ‘Big Five’ personality dimensions, affectivity, and general cognitive ability in a sample of 184 university students (mean age 29.50 years). Hierarchical regression analyses revealed that after controlling for demographic variables, the Big Five personality traits, affectivity, and the cognitive intelligence, the block of ability emotional intelligence scores explained a statistically significant increment of variance in suicidal ideation. It is noteworthy that the predictive power of the ability emotional intelligence appeared to be mostly due to the contribution of its two branch scores–regulation of emotion and understanding of emotion. Findings are discussed with reference to emotional intelligence theory and suicidal behaviors.     

Visual Abilities in Older Adults Explain Age-Differences in Stroop and Fluid Intelligence but Not Face Recognition: Implications for the Vision-Cognition Connection

The associations among age, visual abilities and cognitive abilities were investigated using structural equation modeling. Measures of Visual Acuity, Colour Vision, Contrast Sensitivity, Stroop, Face Recognition and Fluid intelligence (Gf) were administered to a volunteer sample (n = 90) aged 60-87. Visual Acuity was associated with Gf even after controlling for chronological age. Age differences in Stroop were explained entirely by Colour Vision performance. However, neither Visual Acuity nor Colour Vision explained age-differences in Face Recognition. The results show that performance on some neuropsychological tests is influenced by visual ability and challenge the conventional identification of ageing effects on the Stroop task with deficits in frontal executive functioning. Visual abilities do not, however, contribute to age-differences in all cognitive domains suggesting that sensory and cognitive performance declines are not necessarily due to common biological ageing processes.     

Influences of preclinical dementia and impending death on the magnitude of age-related cognitive deficits

The authors examined the influence of preclinical dementia and impending death on the cross-sectional relationship between age and performance in tasks assessing episodic memory, visuospatial skill, and verbal fluency. Increasing age was associated with a general decrease in cognitive performance. In addition, those who were to be diagnosed with dementia or had died by a 3-year follow-up, were older, and performed at a lower level than the remaining sample across all cognitive tasks at baseline. Nevertheless, removal of the preclinical dementia and impending death groups from the original sample affected the cross-sectional age-cognition relations relatively little. This pattern of findings suggests that the biological aging process exerts negative influences on cognitive functioning beyond those resulting from disease and mortality.     

Cognitive Development of Lead Exposed Children from Ages 6 to 15 Years: An Application of Growth Curve Analysis

The effect of lead exposure on cognitive growth patterns was assessed in a longitudinal study of 196 children. Performances on tests of verbal comprehension and perceptual organization (Vocabulary & Block Design, Wechsler Intelligence Scales for Children) were measured at ages 6.5, 11 and 15 years. Growth curve analyses revealed that the quadratic model best described the relationship between test scores and age. Children with higher lead levels, as measured at age 15 years, demonstrated lower verbal comprehension scores over time and greater decline in their rate of Vocabulary development at age 15 years, as compared to children with lower lead levels. Lead exposure was not significantly associated with growth in perceptual organization test scores. Socioeconomic status and maternal intelligence were statistically significantly associated with growth patterns for both test scores, independent of the effects of lead. The findings suggest that lead negatively impacts the developmental progression of specific cognitive skills from childhood through adolescence.     

Cognitive development of lead exposed children from ages 6 to 15 years: an application of growth curve analysis.

The effect of lead exposure on cognitive growth patterns was assessed in a longitudinal study of 196 children. Performances on tests of verbal comprehension and perceptual organization (Vocabulary & Block Design, Wechsler Intelligence Scales for Children) were measured at ages 6.5, 11 and 15 years. Growth curve analyses revealed that the quadratic model best described the relationship between test scores and age. Children with higher lead levels, as measured at age 15 years, demonstrated lower verbal comprehension scores over time and greater decline in their rate of Vocabulary development at age 15 years, as compared to children with lower lead levels. Lead exposure was not significantly associated with growth in perceptual organization test scores. Socioeconomic status and maternal intelligence were statistically significantly associated with growth patterns for both test scores, independent of the effects of lead. The findings suggest that lead negatively impacts the developmental progression of specific cognitive skills from childhood through adolescence.     

Modeling memory decline in older adults: the importance of preclinical dementia, attrition, and chronological age

This longitudinal study examined memory loss in a sample of 391 initially nondemented older adults. Analyses decomposed observed memory loss into decline associated with preclinical dementia, study attrition, terminal decline, and chronological age. Measuring memory as a function of only chronological age failed to provide an adequate representation of cognitive change. Disease progression accounted for virtually all of the memory loss in the 25% of the sample that developed diagnosable dementia. In the remainder of the sample, both chronological age and study attrition contributed to observed memory loss. These results suggest that much of memory loss in aging adults may be attributable to the progression of preclinical dementia and other nonnormative aging processes that are not captured by chronological age.     

A pilot study of urinary peptides as biomarkers for intelligence in old age

Intelligence is an important indicator of physical, mental and social well-being. In old age, intelligence is also associated with a higher quality of life and better health. Heritability studies have shown that there are strong genetic influences, yet unknown, on intelligence, including in old age. Other approaches may be useful to investigate the biological foundations of intelligence differences. Proteomics is a proven technique in revealing biomarkers for certain illnesses. In this pilot study, forty individuals were selected as the cognitive extremes from over 750 people in the Lothian Birth Cohort 1936 (age ~ 72 years) based on their high and low intelligence scores, as measured by a general cognitive ability factor. Urine samples were used as a stable, reliable and abundant source of proteins. Using capillary electrophoresis coupled to mass spectrometry (CE-MS) technology, the proteome of the high and low intelligence groups was determined. Data were calibrated and matched against the human urinary database, to enable comparative assessment. At a nominal significance level (P < 0.05), there were several candidate proteins for association with intelligence, including a zinc finger protein (ZNF653) that has been associated with cognitive deficits, and complement C3 and collagen fragments that have been associated with Alzheimer's disease. Results are preliminary, do not survive multiple testing correction, and require validation. This pilot study shows the potential of this novel proteomics approach, and its applicability to understanding the biological foundations of intelligence differences.