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1.  Cerebral Blood Flow and Gray Matter Volume Covariance Patterns of Cognition in Aging 
Human brain mapping  2012;34(12):10.1002/hbm.22142.
Advancing age results in altered cognitive and neuroimaging-derived markers of neural integrity. Whether cognitive changes are the result of variations in brain measures remains unclear and relating the two across the lifespan poses a unique set of problems. It must be determined whether statistical associations between cognitive and brain measures truly exist and are not epiphenomenal due solely to their shared relationships with age. The purpose of this study was to determine whether cerebral blood flow (CBF) and gray matter volume (GMV) measures make unique and better predictions of cognition than age alone. Multivariate analyses identified brain-wide covariance patterns from 35 healthy young and 23 healthy older adults using MRI-derived measures of CBF and GMV related to three cognitive composite scores (i.e., memory, fluid ability, and speed/attention). These brain-cognitive relationships were consistent across the age range, and not the result of epiphenomenal associations with age and each imaging modality provided its own unique information. The CBF and GMV patterns each accounted for unique aspects of cognition and accounted for nearly all the age-related variance in the cognitive composite scores. The findings suggest that measures derived from multiple imaging modalities explain larger amounts of variance in cognition providing a more complete understanding of the aging brain.
PMCID: PMC3812339  PMID: 22806997
aging; multiple modality imaging; cognitive decline; cerebral blood flow; gray matter volume; multivariate analysis
2.  Effects of first occasion test experience on longitudinal cognitive change 
Developmental psychology  2013;49(11):10.1037/a0032019.
Effects of additional test experience on longitudinal change in five cognitive abilities was examined in a sample of healthy adults ranging from 18 to 80 years of age. Participants receiving experience with parallel versions of the cognitive tests on the first occasion had more positive cognitive change an average of 2.5 years later than participants performing only a single version of the tests on the first occasion. Importantly, these test experience effects were similar in adults of different ages, which implies that retest contributions to cognitive change are comparable among healthy adults between 18 and 80 years of age.
PMCID: PMC3720755  PMID: 23437801
3.  Effects of age and ability on components of cognitive change 
Intelligence  2013;41(5):501-511.
Prior experience with a cognitive task is often associated with higher performance on a second assessment, and these experience effects can complicate the interpretation of cognitive change. The current study was designed to investigate experience effects by obtaining measures of cognitive performance separated by days and by years. The analyses were based on data from 2017 adults with two longitudinal occasions, of whom 948 had also completed a third occasion, with each occasion consisting of three parallel versions of the tests on separate sessions. Change across short intervals was typically positive, and greater among older adults and adults with low levels of cognitive ability, whereas change over intervals of approximately three years was often negative, particularly at older ages. In contrast to the expectation that change over short intervals might be informative about change over longer intervals, relations between short-term change and long-term change were negative, as the individuals who gained the most with assessments separated by days tended to experience the greatest losses across assessments separated by years.
PMCID: PMC3804359  PMID: 24159248
aging; longitudinal; change; retest; cognitive abilities
4.  Within-Cohort Age-Related Differences in Cognitive Functioning 
Psychological science  2013;24(2):123-130.
It is widely accepted that the level of cognitive functioning can be influenced by characteristics of the environment that change over time. Many developmental researchers have referred to these influences as cohort effects, and have used year of birth as the basis for determining cohort membership. Furthermore, age-related differences in cognitive functioning are sometimes assumed to be primarily attributable to cohort differences, which implies that differences between birth cohorts should be much larger than differences within birth cohorts. Comparisons of composite scores for five cognitive abilities in different people tested at different ages in different years revealed that within-cohort differences across ages were often as large as between-cohort differences across ages. These results lead to questions about the practice of relying on birth cohort to represent influences on cognitive functioning associated with temporal shifts in characteristics of the environment.
PMCID: PMC3638128  PMID: 23319401
cohort differences; cross-sectional; aging; cognitive ability; intelligence
5.  Selling points: What cognitive abilities are tapped by casual video games? 
Acta psychologica  2012;142(1):74-86.
The idea that video games or computer-based applications can improve cognitive function has led to a proliferation of programs claiming to “train the brain.” However, there is often little scientific basis in the development of commercial training programs, and many research-based programs yield inconsistent or weak results. In this study, we sought to better understand the nature of cognitive abilities tapped by casual video games and thus reflect on their potential as a training tool. A moderately large sample of participants (n=209) played 20 web-based casual games and performed a battery of cognitive tasks. We used cognitive task analysis and multivariate statistical techniques to characterize the relationships between performance metrics. We validated the cognitive abilities measured in the task battery, examined a task analysis-based categorization of the casual games, and then characterized the relationship between game and task performance. We found that games categorized to tap working memory and reasoning were robustly related to performance on working memory and fluid intelligence tasks, with fluid intelligence best predicting scores on working memory and reasoning games. We discuss these results in the context of overlap in cognitive processes engaged by the cognitive tasks and casual games, and within the context of assessing near and far transfer. While this is not a training study, these findings provide a methodology to assess the validity of using certain games as training and assessment devices for specific cognitive abilities, and shed light on the mixed transfer results in the computer-based training literature. Moreover, the results can inform design of a more theoretically-driven and methodologically-sound cognitive training program.
PMCID: PMC3679476  PMID: 23246789
Working memory; Reasoning; Fluid intelligence; Video games; Cognitive training; Casual games
6.  Localizing age-related individual differences in a hierarchical structure 
Intelligence  2004;32(6):10.1016/j.intell.2004.07.003.
Data from 33 separate studies were combined to create an aggregate data set consisting of 16 cognitive variables and 6832 different individuals who ranged between 18 and 95 years of age. Analyses were conducted to determine where in a hierarchical structure of cognitive abilities individual differences associated with age, gender, education, and self-reported health could be localized. The results indicated that each type of individual difference characteristic exhibited a different pattern of influences within the hierarchical structure, and that aging was associated with four statistically distinct influences; negative influences on a second-order common factor and on first-order speed and memory factors, and a positive influence on a first-order vocabulary factor.
PMCID: PMC3866028  PMID: 24357886
Individual differences; First-/second-order factors; Hierarchical structure
7.  An individual differences analysis of memory control 
Journal of memory and language  2006;55(1):10.1016/j.jml.2006.03.006.
Performance on a wide variety of memory tasks can be hypothesized to be influenced by processes associated with controlling the contents of memory. In this project 328 adults ranging from 18 to 93 years of age performed six tasks (e.g., multiple trial recall with an interpolated interference list, directed forgetting, proactive interference, and retrieval inhibition) postulated to yield measures of the effectiveness of memory control. Although most of the patterns from earlier studies were replicated, only a few of the measures of memory control were reliable at the level of individual differences. Furthermore, the memory control measures had very weak relations with the age of the participant. Analyses examining the relations between established cognitive abilities and variables from the experimental tasks revealed that most of the variables were related only to episodic memory ability.
PMCID: PMC3859462  PMID: 24347812
Control of memory contents; Aging; Individual differences; Memory processing
8.  Within-person variability in state anxiety across adulthood: Magnitude and associations with between-person characteristics 
International journal of behavioral development  2009;33(1):10.1177/0165025408098013.
Across domains of functioning, research has shown substantial within-person variability in a number of different types of variables from one measurement occasion to another. Using data obtained from a large sample (n = 784, 18–97 years) at three separate occasions, we examined properties and correlates of short-term variability in a construct that by definition is prone to fluctuations, namely state anxiety. Our results revealed that participants exhibited sizeable across-occasion variation in state anxiety. The magnitude of variability was unrelated to age, but was associated with a number of individual difference characteristics such as self-reported health, aspects of personality, well-being, and cognition. However, after taking into account mean-level differences in state anxiety, evidence for unique associations of variability was minimal.
PMCID: PMC3859617  PMID: 24347751
adult lifespan; emotion; intraindividual variability; mood
9.  Correlates of individual, and age-related, differences in short-term learning☆ 
Learning and individual differences  2007;17(3):10.1016/j.lindif.2007.01.004.
Latent growth models were applied to data on multitrial verbal and spatial learning tasks from two independent studies. Although significant individual differences in both initial level of performance and subsequent learning were found in both tasks, age differences were found only in mean initial level, and not in mean learning. In neither task was fluid or crystallized intelligence associated with learning. Although there were moderate correlations among the level parameters across the verbal and spatial tasks, the learning parameters were not significantly correlated with one another across task modalities. These results are inconsistent with the existence of a general (e.g., material-independent) learning ability.
PMCID: PMC3859687  PMID: 24347995
Verbal learning; Spatial learning; General learning ability; Intelligence; Growth curve models
10.  Natural and constrained language production as a function of age and cognitive abilities 
Language and cognitive processes  2011;26(10):10.1080/01690965.2010.507489.
Although it is often claimed that verbal abilities are relatively well maintained across the adult lifespan, certain aspects of language production have been found to exhibit cross-sectional differences and longitudinal declines. In the current project age-related differences in controlled and naturalistic elicited language production tasks were examined within the context of a reference battery of cognitive abilities in a moderately large sample of individuals aged 18–90. The results provide support for age-related increases in lexical sophistication and diversity at the discourse level, and declines in grammatical complexity in controlled and naturalistic contexts. Further, age-related decreases in facility with complex grammatical constructions in controlled sentence production were statistically independent of the cognitive abilities assessed in this project.
PMCID: PMC3859871  PMID: 24347752
Grammatical complexity; Ageing; Cognitive abilities
11.  Comment on Greenwood (2007): Functional Plasticity in Cognitive Aging 
Neuropsychology  2007;21(6):10.1037/0894-4105.21.6.678.
In this commentary on P. M. Greenwood’s Functional Plasticity in Cognitive Aging: Review and Hypothesis (2007), the author raises a number of questions stimulated by the article. Although it may be premature to expect answers to those questions, the author argues that they ultimately need to be addressed and answered before Greenwood’s speculations can be considered true hypotheses rather than a conceptual framework.
PMCID: PMC3854971  PMID: 17983280
cognitive aging; conceptual framework; plasticity
12.  An individual difference analysis of false recognition 
The American journal of psychology  2007;120(3):429-458.
Two studies with moderately large samples of participants were conducted to examine correlates of false recognition. In Experiment 1 false recognition of words was found to be a robust and reliable phenomenon at the level of individuals, and the tendency to classify critical lures as old was more closely related to the correct classification of old items as old than to the incorrect classification of unrelated new items as old. False recognition was not significantly related to any of the cognitive abilities that were assessed, including episodic memory, or to other factors such as personality and chronic mood. In Experiment 2 these findings were extended to include dot pattern and face stimuli. Although measures of veridical memory were significantly correlated across the different types of stimulus material, false recognition rates only had modest and generally not significant correlations, which suggests that the tendency to produce false recognitions may be a task-specific characteristic of individuals.
PMCID: PMC3844791  PMID: 17892087
13.  Psychometric Properties of Within-Person Across-Session Variability in Accuracy of Cognitive Performance 
Assessment  2012;19(4):494-501.
Although most psychological assessments are based on measures related to an individual's average level of performance, it has been proposed that measures of variability around one's average may provide unique individual difference information and have clinical significance. The current study investigated properties of within-person variability in measures of performance accuracy in a sample of more than 1,700 healthy adults. Contrary to what has been reported with measures of within-person variability in reaction time, measures of within-person variability in performance accuracy from different cognitive tests had weak correlations with one another, very low stability across time, and near-zero correlations with longitudinal change in cognitive abilities.
PMCID: PMC3632781  PMID: 22389243
aging; cognition; variability
14.  Implications of Within-Person Variability in Cognitive and Neuropsychological Functioning for the Interpretation of Change 
Neuropsychology  2007;21(4):10.1037/0894-4105.21.4.401.
Samples of adults across a wide age range performed a battery of 16 cognitive tests in 3 sessions within an interval of approximately 2 weeks. Estimates of within-person variability across the 3 assessments were relatively large and were equivalent in magnitude to the cross-sectional age differences expected over an interval of 15–25 years. These findings raise questions about the precision of assessments based on a single measurement and imply that it may be difficult to distinguish true change from short-term fluctuation. Because there were large individual differences in the magnitude of this variability, it is proposed that change might be most meaningfully expressed in units of each individual’s own across-session variability.
PMCID: PMC3838958  PMID: 17605573
cognition; aging; longitudinal change; measurement burst
15.  Short-Term Variability in Cognitive Performance and the Calibration of Longitudinal Change 
Recent studies have documented that normal adults exhibit considerable variability in cognitive performance from one occasion to another. We investigated this phenomenon in a study in which 143 adults ranging from 18 to 97 years of age performed different versions of 13 cognitive tests in three separate sessions. Substantial within-person variability was apparent across 13 different cognitive variables, and there were also large individual differences in the magnitude of within-person variability. Because people differ in the amount of short-term variability, we propose that this variability might provide a meaningful basis for calibrating change in longitudinal research. Correlations among the measures of within-person variability were very low, even after we adjusted for reliability, and there was little evidence that increased age was associated with a larger amount of within-person variability.
PMCID: PMC3838959  PMID: 16670183
16.  Multivariate Modeling of Age and Retest in Longitudinal Studies of Cognitive Abilities 
Psychology and aging  2005;20(3):10.1037/0882-7974.20.3.412.
Longitudinal multivariate mixed models were used to examine the correlates of change between memory and processing speed and the contribution of age and retest to such change correlates. Various age- and occasion-mixed models were fitted to 2 longitudinal data sets of adult individuals (N > 1,200). For both data sets, the results indicated that the correlation between the age slopes of memory and processing speed decreased when retest effects were included in the model. If retest effects existed in the data but were not modeled, the correlation between the age slopes was positively biased. The authors suggest that although the changes in memory and processing speed may be correlated over time, age alone does not capture such a covariation.
PMCID: PMC3838960  PMID: 16248701
multivariate models of change; longitudinal methodology; multivariate latent growth curves; practice effects
17.  Efficiency of route selection as a function of adult age 
Brain and cognition  2006;63(3):10.1016/j.bandc.2006.09.006.
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.
PMCID: PMC3838961  PMID: 17079064
Route selection; Aging; Executive functioning
18.  Are individual differences in rates of aging greater at older ages? 
Neurobiology of aging  2011;33(10):2373-2381.
Although differences among people are frequently assumed to increase with age, cross-sectional comparisons of measures of brain structure and measures of cognitive functioning often reveal similar magnitudes of between-person variability across most of adulthood. The phenomenon of nearly constant variability despite systematically lower means with increased age suggests that individual differences in rates of aging may be relatively small, particularly compared to the individual differences apparent at any age. The current study examined between-person variability in cross-sectional means and in short-term longitudinal changes in five cognitive abilities at different ages in adulthood. The variability in both level and change in cognitive performance was found to be similar among healthy adults from 25 to 75 years of age in all five cognitive abilities. Furthermore, the correlations between scores at the first and second occasions were very high, and nearly the same magnitude at all ages. The results indicate that between-person differences in short-term cognitive changes are not inevitably greater among healthy older adults than among young adults.
PMCID: PMC3288400  PMID: 22104734
19.  How General Are the Effects of Trait Anxiety and Depressive Symptoms on Cognitive Functioning? 
Emotion (Washington, D.C.)  2011;12(5):1075-1084.
A total of 3,781 healthy adults between 18 and 97 years of age completed trait anxiety and depressive symptoms inventories and also performed a battery of cognitive tests. Consistent with recent research on cognitive abilities, the cognitive variables could be organized into a hierarchical structure, with 5 first-order abilities and a single g-factor representing the variance common to the first-order abilities at the top of the hierarchy. Analyses were conducted to determine where in this hierarchy effects associated with trait anxiety and depressive symptoms were operating. The results indicated that trait anxiety and depressive symptoms had significant relations at the highest level in the hierarchy of cognitive abilities, but few relations of either characteristic were evident on the cognitive abilities, or on measures of working memory, after controlling influences at the g-factor level.
PMCID: PMC3647465  PMID: 22023357
cognitive abilities; mood effects; level of influence; hierarchical structure of cognitive ability
20.  Does the direction and magnitude of cognitive change depend on initial level of ability? 
Intelligence  2012;40(4):352-361.
Longitudinal change in five cognitive abilities was investigated to determine if the direction or magnitude of change was related to the individual’s ability level. Adults between 18 and 97 years of age performed three versions of 16 cognitive tests on two occasions separated by an average of 2.7 years. In order to control for influences associated with regression toward the mean, level of ability was determined from scores on the first version of the cognitive tests on the first occasion, and across-occasion change was examined on the second and third versions. Change in every cognitive ability was significantly more negative with increased age. However, there was little indication of ability-dependent change in any of the five cognitive abilities, either in differences between composite scores, or in estimates of latent change. Although there are reasons to expect cognitive change to be less negative at either high or low levels of ability, these data suggest that neither the direction nor magnitude of change is related to initial ability when influences of regression toward the mean are controlled.
PMCID: PMC3375710  PMID: 22711949
aging; longitudinal change; ability-dependent change; regression toward the mean
21.  Robust Cognitive Change 
Two major challenges facing researchers interested in cognitive change are that measures of change are often not very reliable, and they may reflect effects of prior test experience in addition to the factors of primary interest. One approach to dealing with these problems is to obtain multiple measures of change on parallel versions of the same tests in a measurement burst design. A total of 783 adults performed three parallel versions of cognitive tests on two occasions separated by an average of 2.6 years. Performance increased substantially across the three sessions within each occasion, and for all but vocabulary ability these within-occasion improvements were considerably larger than the between-occasion changes. Reliabilities of the changes in composite scores were low, but averages of the three changes had larger, albeit still quite modest, reliabilities. In some cognitive abilities individual differences were evident in the relation of prior test experience and the magnitude of longitudinal change. Although multiple assessments are more time consuming than traditional measurement procedures, the resulting estimates of change are more robust than those from conventional methods, and also allow the influence of practice on change to be systematically investigated.
PMCID: PMC3633558  PMID: 22595019
Longitudinal; Aging; Neurocognitive; Reliable change; Measurement burst; Gains and losses
22.  Consequences of Age-Related Cognitive Declines 
Annual review of psychology  2011;63:201-226.
Adult age differences in a variety of cognitive abilities are well documented, and many of those abilities have been found to be related to success in the workplace and in everyday life. However, increased age is seldom associated with lower levels of real-world functioning, and the reasons for this lab-life discrepancy are not well understood. This article briefly reviews research concerned with relations of age to cognition, relations of cognition to successful functioning outside the laboratory, and relations of age to measures of work performance and achievement. The final section discusses several possible explanations for why there are often little or no consequences of age-related cognitive declines in everyday functioning.
PMCID: PMC3632788  PMID: 21740223
cognitive aging; cognitive functioning; job performance; accommodations; typical versus maximal performance
23.  Decomposing age correlations on neuropsychological and cognitive variables 
Individual differences associated with age and various neurological conditions are often found in many different neuropsychological and cognitive variables. These variables are frequently treated as though they were independent of one another, with the results interpreted in terms of effects on task-specific processes. However, an alternative perspective evaluates the breadth of the individual difference influences, and takes relations with other variables into account when considering effects on specific neurocognitive variables. This analytical procedure is illustrated in analyses of the WAIS-IV and WMS-IV standardization data, and of data from the Virginia Cognitive Aging Project.
PMCID: PMC3633567  PMID: 19570312
Cognition; Memory; Aging; Correlation study; Statistical models; Multivariate analysis
24.  Does the Meaning of Neurocognitive Change Change With Age? 
Neuropsychology  2010;24(2):273-278.
Significant declines in longitudinal comparisons of neurocognitive performance are seldom evident until adults are in their 60s or older, but relatively little is known about the existence, or nature, of age-related changes at earlier periods in adulthood. The current research was designed to address this issue by examining characteristics of change in measures from 12 neuropsychological and cognitive tests at different periods in adulthood. Although change was largely positive for adults under about 55 years of age and frequently negative for adults at older ages, the reliabilities of the changes in the neuropsychological and cognitive variables were similar at all ages. Furthermore, there were few systematic relations of age on the reliability-adjusted correlations between the changes in composite scores representing different abilities. These results imply that although neurocognitive declines may not be apparent at young ages because of positive retest effects or other factors, at least in some respects longitudinal changes may have nearly the same meaning across all of adulthood.
PMCID: PMC3633591  PMID: 20230122
aging; cognitive change; longitudinal; reliability
25.  Effects of Age on Time-Dependent Cognitive Change 
Psychological science  2011;22(5):682-688.
Interpretation of cognitive change has been complicated because different influences on change are not easily distinguished. In this study, longitudinal cognitive change was decomposed into a component related to the length of the interval between test occasions (i.e., time-dependent change) and a component unrelated to the test-retest interval (i.e., time-independent change). Influences of age on the two hypothesized components were investigated in a sample of more than 1,500 adults for whom the intervals between test occasions ranged from less than 1 year to more than 8 years. Although overall change was negatively related to age for all seven composite cognitive variables, little or no effect of age was apparent for the time-dependent component of change. The results suggest that the relations between age and cognitive change over intervals of less than 8 years are largely influenced by factors operating at or near the initial test occasion.
PMCID: PMC3631712  PMID: 21467547
longitudinal; cognitive change; aging; retest interval

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