The "common cause hypothesis" of cognitive aging: evidence for not only a common factor but also specific associations of age with vision and grip strength in a cross-sectional analysis.

A prominent hypothesis in cognitive aging is the existence of a common factor that is responsible for age-related deterioration in cognitive and noncognitive processes. A multiple indicators, multiple causes model was used to examine the nature of this common factor and its relationship to age, gender, and the apolipoprotein E (APOE) genotype. The common factor was modeled by using 10 indicator variables with 374 participants aged between 77.4 and 98.7 years. A latent factor was identified, with all indicators except blood pressure loading significantly. This factor could be established in 2 age strata within the sample. After controlling for the effects of gender, APOE, and level of education, direct effects of age were seen on visual functioning and grip strength. APOE was significantly associated with memory but not with the common factor. The findings suggest that a number of specific processes may operate concurrently with any common cause factor.     

Global and domain-specific changes in cognition throughout adulthood

Normative adult age-related decrements are well documented for many diverse forms of effortful cognitive processing. However, it is currently unclear whether each of these decrements reflects a distinct and independent developmental phenomenon, or, in part, a more global phenomenon. A number of studies have recently been published that show moderate to large magnitudes of positive relations among individual differences in rates of changes in different cognitive variables during adulthood. This suggests that a small number of common dimensions or even a single common dimension may underlie substantial proportions of individual differences in aging-related cognitive declines. This possibility was directly examined using data from 1,281 adults 18-95 years of age who were followed longitudinally over up to 7 years on 12 different measures of effortful processing. Multivariate growth curve models were applied to examine the dimensionality of individual differences in longitudinal changes. Results supported a hierarchical structure of aging-related changes, with an average of 39% of individual differences in change in a given variable attributable to global (domain-general) developmental processes, 33% attributable to domain-specific developmental processes (abstract reasoning, spatial visualization, episodic memory, and processing speed), and 28% attributable to test-specific developmental processes. Although it is often assumed that systematic and pervasive sources of cognitive decline only emerge in later adulthood, domain-general influences on change were apparent for younger (18-49 years), middle aged (50-69 years), and older (70-95 years) adults.     

Neuroanatomical substrates of age-related cognitive decline

There are many reports of relations between age and cognitive variables and of relations between age and variables representing different aspects of brain structure and a few reports of relations between brain structure variables and cognitive variables. These findings have sometimes led to inferences that the age-related brain changes cause the age-related cognitive changes. Although this conclusion may well be true, it is widely recognized that simple correlations are not sufficient to warrant causal conclusions, and other types of correlational information, such as mediation and correlations between longitudinal brain changes and longitudinal cognitive changes, also have limitations with respect to causal inferences. These issues are discussed, and the existing results on relations of regional volume, white matter hyperintensities, and diffusion tensor imaging measures of white matter integrity to age and to measures of cognitive functioning are reviewed. It is concluded that at the current time the evidence that these aspects of brain structure are neuroanatomical substrates of age-related cognitive decline is weak. The final section contains several suggestions concerning measurement and methodology that may lead to stronger conclusions in the future.     

Interrelationships among biological markers of aging, health, activity, acculturation, and cognitive performance in late adulthood

In this study a structural equation model of predictors of age differences in cognitive performance in late adulthood was developed. Biological markers of aging (vision, hearing, vibration sense, forced expiratory volume, and grip strength) were used as indicators of a latent variable called BioAge. A sample of 180 community-dwelling women aged 60 to 90 years was assessed. Results showed that BioAge explained all of the age-related variance in cognitive test performance. Physical health and physical activity had direct effects on BioAge. Measures of acculturation explained non-age-related variance in cognitive test performance. Some variables used as biomarkers also explained individual differences in measures of crystallized intelligence and perceptual speed. It is concluded that the association between biomarkers and cognition in old age is due to more than a common statistical association with age.     

Adult Age Differences in Tower of Hanoi Performance: Influence From Demographic and Cognitive Variables

We examined performance in a five-disk version of the Tower of Hanoi (TOH) puzzle, assumed to reflect executive functioning, in population-based samples ranging in age from 35 to 85 years (N ?=?2798). Univariate analyses revealed significant age effects across three TOH measures as reflected by an age-related increase in moves to solution, a gradual slowing of performance, and an increase in rule violations with advanced age. The age-related influence was eliminated, or reduced considerably, when controlling for demographic and cognitive background variables. Across the dependent measures, Block Design and a measure of episodic memory (recall) were the consistent predictors. No effects of education were detected, while significant gender differences, favoring males, were observed for two TOH measures. Taken together, the results suggest that age-related deficits observed in TOH performance reflects an age-related impairment in visuospatial ability in addition to impairments in executive functions.     

Attempted decomposition of age-related influences on two tests of reasoning

Two studies were designed to determine which of several hypothesized components were primarily responsible for the age-related effects on matrix reasoning (Study 1) and analytical reasoning (Study 2). In neither case were the analyses successful because the variables selected to assess the hypothesized components failed to exhibit discriminant validity and also had little unique age-related influences. These results. along with the results of other analyses, suggest that large proportions of the age-related effects on different cognitive variables are shared and are not independent of one another. Implications of these findings for the interpretation of age-related influences on measures of cognitive functioning are discussed.     

Mood, motivation, and misinformation: aging and affective state influences on memory

Normative age differences in memory have typically been attributed to declines in basic cognitive and cortical mechanisms. The present study examined the degree to which dominant everyday affect might also be associated with age-related memory errors using the misinformation paradigm. Younger and older adults viewed a positive and a negative event, and then were exposed to misinformation about each event. Older adults exhibited a higher likelihood than young adults of falsely identifying misinformation as having occurred in the events. Consistent with expectations, strength of the misinformation effect was positively associated with dominant mood, and controlling for mood eliminated any age effects. Also, motivation to engage in complex cognitive activity was negatively associated with susceptibility to misinformation, and susceptibility was stronger for negative than for positive events. We argue that motivational processes underlie all of the observed effects, and that such processes are useful in understanding age differences in memory performance.     

Enhancing the Cognitive Vitality of Older Adults

Aging is associated with decline in a multitude of cognitive processes and brain functions. However, a growing body of literature suggests that age-related decline in cognition can sometimes be reduced through experience, cognitive training, and other interventions such as fitness training. Research on cognitive training and expertise has suggested that age-related cognitive sparing is often quite narrow, being observed only on tasks and skills similar to those on which individuals have been trained. Furthermore, training and expertise benefits are often realized only after extensive practice with specific training strategies. Like cognitive training, fitness training has narrow effects on cognitive processes, but in the case of fitness training, the most substantial effects are observed for executive-control processes.     

Executive functioning as a potential mediator of age-related cognitive decline in normal adults

Critical requirements for the hypothesis that executive functioning is a potential mediator of age-related effects on cognitive functioning are that variables assumed to reflect executive functioning represent a distinct construct and that age-related effects on other types of cognitive functioning are reduced when measures of executive functioning are statistically controlled. These issues were investigated in a study involving 261 adults between 18 and 84 years of age. Although age-related effects on various cognitive abilities were substantially reduced after statistical control of the variance in measures hypothesized to represent executive functioning, there was only weak evidence for the existence of distinct constructs corresponding to executive functioning or to aspects of executive control concerned with inhibition, updating, or time sharing.     

抑制和加工速度与液态智力的年老化

研究抑制能力和加工速度在液态智力年老化过程中的相对作用。被试为142名18~85岁健康成年人,完成包括抑制优势反应、加工速度和液态智力共13项测验。分层回归分析显示,抑制能力与年龄相关的特异性变异,在控制简单的速度变量时较控制复杂的速度变量时更大;结构方程分析表明,对液态智力年老化的中介作用,当选取较复杂的速度变量时加工速度的作用更大,而当选取较简单的速度变量时抑制能力的作用更大。研究结果表明,在液态智力的年老化过程中,除了加工速度的作用之外,抑制能力也起重要的中介作用。该结果为认知年老化的抑制理论和执行衰退假说提供了认知行为学研究的证据,并且对加工速度理论作了有益的补充和修正     

Structural equation models of relationships between exercise and cognitive abilities

Data were obtained from 300 men and women aged 55 to 91. Separate structural equation models of relationships between physical exercise and 3 cognitive performance variables--reaction time, working memory, and reasoning--fit the data well. Other variables in the models were age, health, education, and morale. Age and exercise affected each performance variable directly; education had a direct effect on reasoning only. There were also indirect effects of age and health on performance variables, mediated through exercise. The main hypothesis of the study, that exercise contributes to performance, was supported. A large decrease in model fit resulted when the path from exercise to each performance variable was deleted. Hypotheses that age-related deficits are primarily accounted for by lack of exercise or by poor health were not supported.     

What needs to be explained to account for age-related effects on multiple cognitive variables?

Structural equation methodology was used to investigate age-related influences across a number of cognitive variables in 204 adults ranging from 18 to 91 years of age with a hierarchical structure that contained 4 1st-order factors and 1 2nd-order common factor. Direct age relations were found to the common factor as well as to 1st-order speed and memory factors. Replicability of the findings was explored by investigating the same structure of age relations, using 2 different data sets, and a similar patten was found in each. These results suggest that at least 3 statistically distinct types of age-related influences are operating on a wide variety of cognitive variables and presumably require separate explanatory mechanisms.     

Constraints on theories of cognitive aging

There is currently little consensus regarding what must be explained by theories of cognitive aging. In the present article, four empirical generalizations that seem to imply certain constraints in theorizing are identified. These generalizations, and their possible implications or constraints, are that (1) age-related differences are found in a wide range of cognitive variables, implying that either a large number of specific factors or a small number of general factors must be contributing to the age-related differences; (2) the age-related influences on different cognitive variables are not independent, and unique age-related influences appear to be few in number and small in magnitude, implying that some fairly general factors need to be postulated to account for the shared age-related influences; (3) only a small proportion of distinct age-related variance occurs late in practice and at long presentation durations, implying that adequate explanations must include factors operating when the individuals are just beginning to perform the task and when the stimuli can first be registered; and (4) measures of how quickly very simple cognitive tasks can be performed share considerable age-related variance with many cognitive variables, implying that factors related to simple processing efficiency need to be incorporated into the explanations.     

Environmental topography and postural control demands shape aging-associated decrements in spatial navigation performance

This study tests the hypothesis that aging-induced cognitive permeation of sensorimotor functions contributes to adult age differences in spatial navigation performance. Virtual maze-like museums were projected in front of a treadmill. Sixteen 20-30-year-old men and sixteen 60-70-year-old men performed a way-finding task in city-block or variable topographies while walking with or without support. Walking support attenuated age-related decrements in navigational learning. Navigation load increased trunk-angle variability for older adults only. Age differences in spatial knowledge persisted despite perfect place-finding performance. City-block topography was easier than variable topography for younger adults only, indicating age-related differences in reliance on spatial relational learning. Attempts at supporting older adults' navigation performance should consider sensorimotor/cognitive interactions and qualitative differences in navigational activity.     

Reply to Commentary by Collins: Distinguishing Proximal and Distal Levels of Explanation

Two analytical methods are proposed to evaluate the extent to which the age-related influences in a set of variables are independent of one another. Application of the methods to 16 different data sets, representing a total of 169 variables and 4505 subjects, reveals that as few as one or two distinct factors may be sufficient to account for a large proportion of the age-related variance in a variety of cognitive variables. These results therefore imply that a relatively small number of independent "causes" may be responsible for a substantial percentage of the age-related declines apparent in many measures of cognitive functioning.     

Age-cognition relations and the personality trait of Conscientiousness

Increasing age has been found to correlate with a decrease in many cognitive abilities and an increase in the personality trait of Conscientiousness. The first goal of this study was to examine whether an age-related decline in cognitive abilities, in particular Fluid ability, accounts for the age-related increase in Conscientiousness. The second goal was to investigate whether the role of cognitive abilities in the relation between age and Conscientiousness is similar among people of different levels of education.Our results support the conclusion that the relation between age and Conscientiousness is mediated by fluid ability and working memory abilities, and that these effects are stronger in people with lower levels of education.Altogether, these findings are consistent with the hypothesis that age differences in characteristics such as persistence, self-motivation and dutifulness may help compensate for age differences in cognition.     

Modeling age and retest processes in longitudinal studies of cognitive abilities

Mixed effects models were used to examine the separate effects associated with age and retest on changes in various cognitive abilities. Individuals (N > 800) ranging in age from 40 to 70 years at the 1st measurement occasion were assessed with measures of memory, spatial abilities, and speed on 4 occasions. All cognitive abilities showed decline associated with increased age and improvement across the 4 measurement occasions. The age-related effects were similar across variables, but the practice effects were largest for memory and smallest for speed. When retest effects were not included in the models, the age-related effects were underestimated, with the magnitude of bias depending on the size of the ignored retest effects. It is suggested that both age and retest should be modeled simultaneously when analyzing longitudinal data because part of the change across occasions may be attributable to practice or reactive effects.     

Efficiency of route selection as a function of adult age

Two tasks hypothesized to assess the efficiency of route selection were administered to 328 adults ranging from 18 to 93 years of age. Increased age was associated with slower completion of mazes, even after adjusting for differences in perceptual-motor speed, and with longer and less accurate routes in a task in which participants were asked to visit designated exhibits in a zoo. The route selection measures were correlated with measures hypothesized to represent executive functioning, such as the number of categories in the Wisconsin card sorting test and the number of words generated in a category fluency test. However, most of the age-related influences on the measures from the route selection tasks were shared with age-related effects on established cognitive abilities, which implies that the same mechanisms may account for the relations of age on both sets of variables.     

Working memory and arithmetic calculation in children: the contributory roles of processing speed, short-term memory, and reading

The cognitive underpinnings of arithmetic calculation in children are noted to involve working memory; however, cognitive processes related to arithmetic calculation and working memory suggest that this relationship is more complex than stated previously. The purpose of this investigation was to examine the relative contributions of processing speed, short-term memory, working memory, and reading to arithmetic calculation in children. Results suggested four important findings. First, processing speed emerged as a significant contributor of arithmetic calculation only in relation to age-related differences in the general sample. Second, processing speed and short-term memory did not eliminate the contribution of working memory to arithmetic calculation. Third, individual working memory components--verbal working memory and visual-spatial working memory--each contributed unique variance to arithmetic calculation in the presence of all other variables. Fourth, a full model indicated that chronological age remained a significant contributor to arithmetic calculation in the presence of significant contributions from all other variables. Results are discussed in terms of directions for future research on working memory in arithmetic calculation.     

Only time will tell: cross-sectional studies offer no solution to the age-brain-cognition triangle: comment on Salthouse (2011)

Salthouse (2011) critically reviewed cross-sectional and longitudinal relations among adult age, brain structure, and cognition (ABC) and identified problems in interpretation of the extant literature. His review, however, missed several important points. First, there is enough disparity among the measures of brain structure and cognitive performance to question the uniformity of B and C vertices of the ABC triangle. Second, age differences and age changes in brain and cognition are often nonlinear. Third, variances and correlations among measures of brain and cognition frequently vary with age. Fourth, cross-sectional comparisons among competing models of ABC associations cannot disambiguate competing hypotheses about the structure and the range of directed and reciprocal relations between changes in brain and behavior. We offer the following conclusions, based on these observations. First, individual differences among younger adults are not useful for understanding the aging of brain and behavior. Second, only multivariate longitudinal studies, age-comparative experimental interventions, and a combination of the two will deliver us from the predicaments of the ABC triangle described by Salthouse. Mediation models of cross-sectional data represent age-related differences in target variables but fail to approximate time-dependent relations; thus, they do not elucidate the dimensions and dynamics of cognitive aging.