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.

Aging and measures of processing speed.

Many variables have been assumed to reflect speed of processing, and most are strongly related to age in the period of adulthood. One of the primary theoretical questions with respect to aging and speed concerns the relative roles of specific and general age-related effects on particular speed variables. Distinguishing between specific (or unique) and general (or shared) age-related influences on measures of speed has been complicated, in part because the issues are sometimes framed in terms of extreme all-or-none positions, and because few researchers have employed analytical procedures suitable for estimating the relative contributions of each type of influence. However, recent methods focusing on partitioning age-related variance have indicated that large proportions of the age-related effects on individual speed variables are shared with age-related effects on other variables. Although these theoretical ideas and analytical procedures are fairly new, they may be relevant to a variety of psychophysiological or neurobiological variables.

Effects of aging on efficiency of task switching in a variant of the trail making test.

The Trail Making Test (TMT; R. M. Reitan, 1958, 1992) is extensively used in research in neuropsychology and in aging, in part because it has been postulated to reflect executive processes, such as planning and switching. However, neurocognitive and individual-difference-based analyses of this test are complicated because of different spatial arrangements of targets, the use of letters only in Version B, and potential order effects when Version A is administered prior to Version B. The present article examines a variant of a TMT (called the Connections Test) that attempts to remedy these deficiencies. A structural equation model suggested that there were no direct effects of age on either the nonalternating or alternating versions of the Connections Test (analogous to TMT Versions A and B, respectively); rather, all age-related effects were mediated through effects on perceptual speed. Moreover, although the nonalternating and alternating versions were strongly related to one another, only the latter had significant independent relations with measures of higher order cognition.

Item analyses of age relations on reasoning tests.

Analyses at the level of individual items were conducted on 11 data sets representing various combinations of participant samples and tests of reasoning. The magnitude of the relations between age and solution accuracy did not vary systematically across a wide range of item difficulty, although there was some evidence for independent age-related influences on the more difficult items. The results were tentatively interpreted as reflecting the operation of at least 2 types of age-related effects on tests of reasoning, 1 common to all items and 1 sensitive to the greater processing demands associated with more difficult items.

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.

From the present to the future. Commentary on Luszcz and Bryan.

Recent research on aging and memory is admirably reviewed in the article by Luszcz and Bryan. In particular, they clearly describe the major theoretical perspectives proposed to account for the relations between age and memory at the current time. This commentary focuses on several issues that seem likely to emerge as important themes in future research in this area, such as construct validity and multivariate analytical procedures.

Task decomposition analysis of intertrial free recall performance on the Rey Auditory Verbal Learning Test in normal aging and Alzheimer's disease.

Task decomposition provides supplementary data that complement traditionally computed performance indexes of multi-trial list learning. Both traditional and decomposition approaches can be combined to permit a thorough assessment of multiple aspects of learning and memory in patients with memory impairment. We applied task decomposition to investigate the relative roles of acquisition and consolidation in mediating the multi-trial learning deficit in patients with Alzheimer's disease. This goal was accomplished by decomposing recall performance across the five study-and-test trials of the Rey Auditory Verbal Learning Tests into measures that presumably tap intertrial acquisition and intertrial consolidation. As compared to matched controls, patients diagnosed with mild Alzheimer's disease showed lower gained access across trials, indicating that Alzheimer's disease impairs the ability to produce a stable memory representation of new material in long-term memory. Additionally, patients with Alzheimer's disease manifested higher lost access, which suggests that deficient consolidation leading to rapid intertrial forgetting also contributes to their poor learning. We argue that analytically decomposing learning curves will help both in uncovering the cognitive processes that underlie disease-related learning deficits in persons with memory disorders and can help to characterize potential areas for remediation.

Predictors of crossword puzzle proficiency and moderators of age-cognition relations.

Four studies, each with approximately 200 adults between the ages of 18 and 80, were conducted to address two major goals. The first goal was to examine the relative contributions of different factors to the successful solution of crossword puzzles. Correlations and structural equation analyses revealed that general knowledge is the strongest predictor of crossword puzzle proficiency. Surprisingly, abstract reasoning ability, as measured by several different tests, had no direct relation to puzzle proficiency. The second goal of the project was to examine moderators of the relations between age and measures of both fluid and crystallized cognition. The results provide no evidence to suggest that amount of crossword puzzle experience reduces age-related decreases in fluid cognition or enhances age-related increases in crystallized cognition.

Neuropsychological test performance in the acquired immunodeficiency syndrome: independent effects of diagnostic group on functioning.

Individuals infected with the acquired immunodeficiency syndrome (AIDS) are at risk for developing cognitive impairment. The extent to which the impairment represents the results of a single factor accounting for a wide degree of cognitive dysfunction, or is the result of the combined effects of multiple factors, has not been determined. In the present study, we analyzed data from 134 patients with AIDS and 105 HIV- controls using a recently developed analytical procedure. The results revealed that, by and large, the test variables shared a significant amount of variance related to disease status. Hence the AIDS-related influences on cognition are shared and thus cannot be considered independent. Two tests, Digit Symbol Substitution, and the primary measure of verbal free recall, had a direct relationship with the group variable (AIDS vs. controls). These results suggest that a single factor is sufficient to account for a large proportion of the AIDS-related variance on a wide variety of neuropsychological tests.

Shared age-related influences on cognitive and noncognitive variables.

Analyses of new data and of previously published data were conducted to examine the degree to which age-related variance was shared across cognitive and noncognitive variables and to investigate possible alterations in the composition of a factor common to all variables as a function of age. The results indicated that measures of visual acuity, grip strength, and blood pressure shared age-related variance with measures of perceptual speed, episodic memory, spatial visualization, and inductive reasoning. However, although the cognitive variables shared similar amounts of variance in age-restricted and age-partialed analyses, the variance shared between cognitive and noncognitive variables was substantially reduced after controlling the influence of age.

Independence of age-related influences on cognitive abilities across the life span.

Age-related increases in childhood and age-related decreases in adulthood have been reported for a wide variety of cognitive variables, but relatively little research has addressed the question of the independence of these influences. In this project, cross-sectional life span data (age 5 to 94 years) from the nationally representative sample used to establish the norms for the Woodcock-Johnson Psycho-Educational Battery (R. W. Woodcock & M. B. Johnson, 1989, 1990) were subjected to several types of analyses. The results indicated that the majority of age-related differences appear to be shared across different cognitive variables and are well predicted by individual differences in higher order factors. These findings suggest that the role of task-specific interpretations of developmental differences in cognition needs to be reevaluated to take into consideration the lack of independence of age-related influences on a variety of cognitive variables.

Independent effects of Alzheimer's disease on neuropsychological functioning.

A new analytical procedure, single common factor analysis, was carried out on the data from a relatively large sample of normals (n = 101) and patients with Alzheimer's disease (AD; n = 180) to examine the extent to which there were independent effects of disease status on different neuropsychological variables. This technique uses structural equation methods to determine what all of the variables have in common, and then controls this common factor when examining the relationship between diagnostic group and each individual test variable. To the extent that AD represents the sum of independent breakdowns of different information processing domains, then there should be sets of variables that have weak or nonexistent links to the other variables. However, the results revealed that a large proportion of the AD-related effects on test scores was shared and was not independent of the AD-related effects on other variables.

The effects of age and experience on memory for visually presented music.

Increased age is often associated with lower levels of performance in tests of memory for spatial information. The primary question in the current study was whether this relationship could be moderated as a function of one's relevant experience and/or knowledge. Stimulus materials consisted of short (7-11 note), visually presented musical melodies and structurally equivalent nonmusical stimuli. Participants (N = 128) were recruited from a wide range of age and experience levels. Although there were strong main effects of age and experience on memory for music, there was no evidence that the age-related differences in memory for these stimuli were smaller for individuals with moderate to large amounts of experience with music.

Normative data for equivalent, parallel forms of the Judgment of Line Orientation Test.

The Judgment of Line Orientation Test (JLO; Benton, Hamsher, Varney, & Spreen, 1983) permits assessment of visuospatial processing without making demands on motor skills. However, its administration can be time-intensive and frustrating for patients, particularly when used in a geriatric population. We present a single set of normative data to be used for both the odd-item and even-item forms derived from Form V of the JLO based on responses from a healthy geriatric sample. Mean scores and distributions of odd-item and even-item forms were nearly identical, and both forms showed significant correlations with the Developmental Test of Visual- Motor Integration. Cross-validation using the odd form of the JLO on an independent sample from a different geographic location suggested good generalizability of the normative data. We conclude that these JLO short-form normative data may be used in clinical screening situations or when serial assessments are needed.

Meta-analyses of age-cognition relations in adulthood: estimates of linear and nonlinear age effects and structural models.

A meta-analysis was conducted on 91 studies to derive a correlation matrix for adult age, speed of processing, primary-working memory, episodic memory, reasoning, and spatial ability. Structural equation modeling with a single latent common cognitive factor showed that all cognitive measures shared substantial portions of age-related variance. A mediational model revealed that speed of processing and primary-working memory appear to be important mediators of age-related differences in the other measures. However, not all of the age-related influences were mediated. An examination of quadratic age effects and correlational patterns for subsamples under and over 50 years of age revealed that (a) negative age-cognition relations were significant for the 18- to 50-year-old sample and (b) the age-related decline accelerated significantly over the adult life span for variables assessing speed, reasoning, and episodic memory.

Controlled and automatic forms of memory and attention: process purity and the uniqueness of age-related influences.

Estimates of controlled and automatic processes hypothesized to underlie performance in a memory task and in an attention task were derived for 115 participants from 18 to 78 years of age using the process-dissociation procedure. Participants also performed speed and neuropsychological tests that were suspected to be negatively related to age. Process estimates showed good reliability (from .76 to .98), and the qualitative distinction between processes was supported by the overall pattern of correlations among measures. However, only estimated automatic processes exhibited unique variance, as they were either weakly related or unrelated both to performance on the other tests and to each other. Estimates of the control processes, in contrast, shared considerable variance with measures from other tests, and there were no unique, or independent, age-related effects on these measures. The results highlight the need to distinguish between process purity and the uniqueness of age-related influences in accounting for age differences in cognition.

Examination of age-related deficits on the Wisconsin Card Sorting Test.

Adult age differences in Wisconsin Card Sorting Test (WCST) measures were examined before and after statistical control of age-related differences in measures of feedback usage, working memory, and perceptual-comparison speed. The proportion of age-related variance associated with a summary measure of WCST performance was greatly reduced after controlling for measures of feedback usage, working memory, and perceptual-comparison speed. Furthermore, the age-related variance associated with the feedback-usage measure was reduced after controlling for working memory and perceptual-comparison speed measures. These results are consistent with the idea that age-related performance differences in the WCST are partially mediated by adult age differences in feedback usage and that age differences in feedback usage are mediated by age differences in working memory, which are in turn-mediated by age-related reductions in processing speed, indexed by measures of perceptual-comparison speed.

Interrelations of age, visual acuity, and cognitive functioning.

It has recently been suggested that a large proportion of the age-related influences on many measures of cognitive functioning is mediated through a single common factor. This hypothesis has been supported by the discovery that much of the age-related variance in different cognitive measures is shared, and is not distinct or independent. These earlier results were replicated in this project, and it was also discovered that measures of corrected visual acuity and processing speed share a very large proportion of the age-related variance in measures of working memory, associative learning, and concept identification. The apparent implication is that the common factor that appears to contribute to age-related differences in many cognitive measures is quite broad and may reflect a relatively general reduction in central nervous system functioning.

The processing-speed theory of adult age differences in cognition.

A theory is proposed to account for some of the age-related differences reported in measures of Type A or fluid cognition. The central hypothesis in the theory is that increased age in adulthood is associated with a decrease in the speed with which many processing operations can be executed and that this reduction in speed leads to impairments in cognitive functioning because of what are termed the limited time mechanism and the simultaneity mechanism. That is, cognitive performance is degraded when processing is slow because relevant operations cannot be successfully executed (limited time) and because the products of early processing may no longer be available when later processing is complete (simultaneity). Several types of evidence, such as the discovery of considerable shared age-related variance across various measures of speed and large attenuation of the age-related influences on cognitive measures after statistical control of measures of speed, are consistent with this theory.

Where in an ordered sequence of variables do independent age-related effects occur?

A series of regression analyses was conducted to determine which variables in an ordered sequence had significant age-related effects after control of the immediately preceding variable in the sequence. Independent age-related effects in these types of analyses are particularly interesting because they represent age-related influences that are not mediated through earlier variables. A total of 56 analyses are reported with ordered variables representing: (a) successive trials or sessions in learning; (b) progressively more intervening events during the retention interval of a memory task; (c) successively longer stimulus presentation durations; and (d) increased processing complexity. In most of the analyses a very large proportion of the age-related effects on later variables was found to be mediated through earlier variables in the sequence.