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.     

Structural constraints on process explanations in cognitive aging

Much of the current research in the area of cognitive aging has been focused on investigating specific processes presumed to be responsible for the age differences observed in particular cognitive tasks. A central thesis of this article is that age-related effects on cognitive variables seldom occur in isolation, and hence, they are best interpreted in the context of the structural interrelations that exist among variables and the relations of age on that organizational structure. Results from analyses of 2 separate data sets suggest that large proportions of the age-related effects across a wide range of cognitive variables are shared and that independent, or unique, age-related effects often contribute relatively little to the age differences observed in many cognitive variables. These findings imply that it is important to consider the structure within which a variable occurs when attempting to investigate the processes responsible for age-related differences on that variable.     

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.     

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.     

Alternative Models of Price Behavior in Dyadic Negotiations: Market Prices, Reservation Prices, and Negotiator Aspirations

Three competing predictors of price are manipulated in a two-party distributive negotiation. These include prevailing market prices, negotiator reservation prices, and negotiator aspirations. We offer a cognitive interpretation of how each type of information is incorporated into the negotiator′s thought processes as an alternative cognitive reference point. In two studies varying the levels of these three factors, only reservation prices, not prevailing market prices or negotiator aspirations, account for significant variance in negotiated outcomes. Discussion is offered, suggesting that the negotiator as decision maker may experience a "dominant reference point" effect. When multiple pieces of relevant information are available, the negotiator may only be able to focus on one of them. Among the three predictors studied, the reservation price may be cognitively interpreted as the most absolute limit.     

Which is the real intelligence? A reply to Robinson (1999)

Robinson's ([Robinson, D.L. (1999). The ‘IQ’ factor: implications for intelligence theory and measurement. Personality and Individual Differences, 27, 715–735]) arguments that crystallized intelligence represents the “one valid intelligence factor” are disputed. It is argued that Robinson seriously underestimated the relevance of fluid abilities to “intelligence”, by using an inappropriate criterion for assessing the intelligence-saturation of cognitive ability variables. The relevance of fluid and crystallized abilities to popular, psychometric, and biological conceptions of intelligence is discussed, and the issue of age-related changes in fluid and crystallized intelligence is also addressed.     

The matching law

The matching law may be viewed either as an empirical generalization, and therby subject to disproof, or as part of a system of equations used to define the utility (“value”) of a reinforcer. In the latter case it is tautologous, and not subject to disproof within the defining context. A failure to obtain matching will most often be a signal that the independent variables have not been properly scaled. If, however, the proper transformations have been made on the independent variables, and matching is not obtained, the experimental paradigm may be outside the purview of the matching law. At that point, reinterpretations or revisions of the law are called for. The theoretical matching law is but one of many possible ways to define utility, and it may eventually be rejected in favor of a more useful definition.     

Aged rats are impaired on an attentional set-shifting task sensitive to medial frontal cortex damage in young rats

Normal aging is associated with disruption of neural systems that subserve different aspects of cognitive function, particularly in the hippocampus and frontal cortex. Abnormalities in hippocampal function have been well investigated in rodent models of aging, but studies of frontal cortex function in aged rodents are few. We tested young (4–5 mo old) and aged (27–28 mo old) male Long-Evans rats on an attentional set-shifting task modified slightly from previous publication. After training on two problems in which the reward was consistently associated with the same stimulus dimension, and a reversal of one problem, a new problem was presented in which the reward was consistently associated with the previously irrelevant stimulus dimension (extradimensional shift [EDS]). Aged rats as a group were significantly impaired on the EDS, although some individual aged rats performed as well as young rats on this phase. In addition, some aged rats were impaired on the reversal, although a group effect did not reach significance in this phase. Impairment in neither reversal nor EDS was associated with impairments in spatial learning in the Morris water maze. Young rats with neurotoxic lesions of medial frontal cortex are also selectively impaired on the EDS. These results indicate that normal aging in rats is associated with impaired medial frontal cortex function. Furthermore, age-related declines in frontal cortex function are independent of those in hippocampal function. These results provide a possible basis for correlating age-related changes in neurobiological markers in frontal cortex with cognitive decline.     

Decomposing the relationship between cognitive functioning and self-referent memory beliefs in older adulthood: what’s memory got to do with it?

With advancing age, episodic memory performance shows marked declines along with concurrent reports of lower subjective memory beliefs. Given that normative age-related declines in episodic memory co-occur with declines in other cognitive domains, we examined the relationship between memory beliefs and multiple domains of cognitive functioning. Confirmatory bi-factor structural equation models were used to parse the shared and independent variance among factors representing episodic memory, psychomotor speed, and executive reasoning in one large cohort study (Senior Odyssey, N = 462), and replicated using another large cohort of healthy older adults (ACTIVE, N = 2802). Accounting for a general fluid cognitive functioning factor (comprised of the shared variance among measures of episodic memory, speed, and reasoning) attenuated the relationship between objective memory performance and subjective memory beliefs in both samples. Moreover, the general cognitive functioning factor was the strongest predictor of memory beliefs in both samples. These findings are consistent with the notion that dispositional memory beliefs may reflect perceptions of cognition more broadly. This may be one reason why memory beliefs have broad predictive validity for interventions that target fluid cognitive ability.     

Reliability, Distribution, and Validity of Age-Related Cognitive Deficits in the Morris Water Maze

In the present study, F-344 rats throughout 1.5 to 26 months of age were tested in the reference memory version, a moving-platform repeated acquisition version, and in a cued platform version of the Morris water maze. The results suggest that: (1) performance in the water maze declines continuously, beginning at the earliest age, and very closely fits a linear function; (2) there are robust, reliable differences between individuals in terms of their performance in the Morris water maze, but chronological age accounts for only a fraction of the variance between individuals; (3) there is no evidence of a bimodal distribution among aged rats—there is no distinct subgroup of individuals that performs so poorly that they are qualitatively different from the majority of the population, and distinctions between “impaired” and “unimpaired” subjects must be based on arbitrary criteria that may not be consistent from one study to the next; (4) age-related deficits in the Morris water maze may not be restricted to learning and memory, but may also include deficits in attention, the ability to process spatial information, and/or the ability to develop efficient spatial search strategies; and (5) swim distance is the most appropriate measure of cognitive function in the Morris water maze, but the relationship between this measure and other measures of noncognitive function make it clear that swim distance may not be a pure measure of cognitive function. Although the Morris water maze remains a valuable preclinical test with better validity and specificity than many other behavioral tests, measures of performance in the Morris water maze should not be considered synonymous with cognitive function.     

Construct validity and age sensitivity of prospective memory

We administered four prospective memory tasks to 330 adults between 18 and 89 years of age to investigate the relationship among the measures of performance in the four tasks, as well as the relationship of the prospective memory measures to age, other cognitive abilities, and noncognitive factors. The four prospective memory variables were found to exhibit both convergent and discriminant validity, indicating that prospective memory ability appears to represent a distinct dimension of individual differences. The prospective memory construct was significantly related to other cognitive abilities, such as executive functioning, fluid intelligence, episodic memory, and perceptual speed, but it was only weakly related to self-ratings of (primarily retrospective) memory and to personality traits. Although a substantial proportion of the age-related variance on the prospective memory construct was shared with other cognitive abilities, we also found some evidence of unique, statistically independent, age-related influences on prospective memory.     

Evaluating the interdependence of aging-related changes in visual and auditory acuity,balance, and cognitive functioning

High proportions of shared age-related variance are found among measures of perceptual acuity, balance, muscle strength, and cognitive capabilities in age-heterogeneous, cross-sectional studies. Reliance on cross-sectional studies is problematic, however, because associations may arise from age-related mean trends. Narrow age-cohort samples provide an alternative basis for testing hypotheses regarding associations among rates of change. Cross-domain associations were evaluated in combined 75-year-old cohort samples from Denmark, Finland, and Sweden. In general, no consistent associations were found across sensory, balance, strength, and cognitive domains. These findings indicate that the effects of aging on sensory acuity, balance, and cognitive functioning are likely to be largely independent, multidimensional, and complex at the level of the individual.     

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.     

Cross-sectional age variance extraction: what's change got to do with it?

In cross-sectional age variance extraction (CAVE), age, the indicator of a hypothesized developmental mechanism, and a developmental outcome are specified as independent, mediator, and target variables, respectively, to test hypotheses about behavioral development. We show that: (a) longitudinal change in a mediator variable accounting for substantial cross-sectional age-related variance in the target variable need not correlate with the target variable's longitudinal change; and, conversely, (b) longitudinal change in a mediator not sharing cross-sectional age-related variance with the target variable may nevertheless correlate highly with that variable's longitudinal change. We discourage use of CAVE for testing multivariate hypotheses about behavioral development.     

Why do older adults have difficulty following conversations?

Age-related declines in understanding conversation may be largely a consequence of perceptual rather than cognitive declines. B. A. Schneider, M. Daneman, D. R. Murphy, and S. Kwong-See (2000) showed that age-related declines in comprehending single-talker discourse could be eliminated when adjustments were made to compensate for the poorer hearing of older adults. The authors used B. A. Schneider et al.'s methodology to investigate age-related differences in comprehending 2-person conversations. Compensating for hearing difficulties did not eliminate age-related differences when the 2 talkers were spatially separated by 9 degrees or 45 degrees azimuth, but it did when the talkers' contributions came from one central location. These findings suggest that dialogue poses more of a problem for older than for younger adults, not because of the additional cognitive requirements of having to follow 2 talkers rather than 1, but because older adults are not as good as younger adults at making use of the auditory cues that are available for helping listeners perceptually segregate the contributions of 2 spatially separated talkers.     

Age-related changes in brain–behaviour relationships: Evidence from event-related functional MRI studies

A fundamental aim of studies in neurocognitive ageing is to understand age-related changes in brain–behaviour relationships. Neuroimaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) can be used for observation of these age-related changes only if the assumption of age-equivalent relations between neural activity and haemodynamic activity is valid. In one study, we characterised age-related differences in the coupling of the haemodynamic response to neural activity and found greater voxel-wise noise in older than in younger adults, but age-equivalent signal magnitude. These results suggested that alternative techniques may be necessary for analysing age-related differences in neuroimaging data. In a second study, we utilised one alternative method for comparing fMRI activation between younger and older adults performing a working memory (WM) task. Across three experiments, the results suggested that age-related functional changes in fMRI activation can be isolated to dorsolateral prefrontal cortex (PFC) during memory retrieval. These results suggest a plausible model for WM decline with normal ageing. In a third study we propose and test a model of age-related PFC dysfunction that may account for these and other age-related differences in cognitive performance.     

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.     

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.     

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.     

The prediction of intelligence in preschool children using alternative models to regression

Statistical prediction of an outcome variable using multiple independent variables is a common practice in the social and behavioral sciences. For example, neuropsychologists are sometimes called upon to provide predictions of preinjury cognitive functioning for individuals who have suffered a traumatic brain injury. Typically, these predictions are made using standard multiple linear regression models with several demographic variables (e.g., gender, ethnicity, education level) as predictors. Prior research has shown conflicting evidence regarding the ability of such models to provide accurate predictions of outcome variables such as full-scale intelligence (FSIQ) test scores. The present study had two goals: (1) to demonstrate the utility of a set of alternative prediction methods that have been applied extensively in the natural sciences and business but have not been frequently explored in the social sciences and (2) to develop models that can be used to predict premorbid cognitive functioning in preschool children. Predictions of Stanford–Binet 5 FSIQ scores for preschool-aged children is used to compare the performance of a multiple regression model with several of these alternative methods. Results demonstrate that classification and regression treesprovided more accurate predictions of FSIQ scores than does the more traditional regression approach. Implications of these results are discussed.