Short-term fluctuations in elderly people's sensorimotor functioning predict text and spatial memory performance: The Macarthur Successful Aging Studies

Intra-individual variability adaptively increases following inhibition training during middle childhood

There is ongoing debate on the relationship between intra-individual variability (IIV) of cognitive processes and task performance. While psychological research has traditionally assumed that lower intra-individual variability (IIV) aids consistent task performance, some studies suggest that greater IIV can also be adaptive, especially when flexible responding is required. Here we selectively manipulate inhibitory control (Stopping) and response speed (Going) by means of a training paradigm to 1) assess how this manipulation impacts Stopping IIV and its relationship to task performance, and 2) replicate previous findings showing that reductions in Going IIV are adaptive. A group of 208 6-13-year-old children were randomly allocated to an 8-week training targeting Stopping (experimental group) or Going (control group). The stop signal task was administered before and after training. Training Stopping led to adaptive increases in Stopping IIV, where greater flexibility in cognitive processing may be required to meet higher task demands. In line with previous studies, training Going led to adaptive reductions in Going IIV, which allows more consistent and efficient Going performance. These findings provide systematic and causal evidence of the process-dependent relationship of IIV and task performance in the context of Stopping and Going, suggesting a more nuanced perspective on IIV with implications for developmental, ageing and intervention studies.

Intra-individual variability identifies individuals vulnerable to contextually induced executive lapses

Contextual stressors, such as engagement in burdensome emotion regulation known as expressive suppression (ES), can result in transient but clinically meaningful decrement in performance on measures of executive functioning (EF). The goal of the present investigation was to examine whether intra-individual variability (IIV-I), which has been identified as an indicator of cognitive weakness, could serve as a marker of vulnerability to EF decrements due to both naturally-occurring and experimentally-manipulated ES.

In Study 1, 180 cognitively healthy older adults completed the Push-Turn-Taptap (PTT) task to assess IIV-I, four Delis-Kaplan Executive Function System (D-KEFS) subtests to assess EF, and the Burden of State Emotion Regulation Questionnaire (B-SERQ) to assess naturally-occurring ES. In Study 2, a subset (n = 81) of participants underwent experimental manipulation to induce ES, followed by second administration of the D-KEFS to examine ES-induced decrements in EF.

In Study 1, hierarchical linear regression yielded a significant interaction between ES and IIV-I as predictors of EF performance, demonstrating that high ES was associated with low EF only among individuals with high IIV-I. In Study 2, repeated measures ANOVA demonstrated an interaction between time (pre- vs. post- manipulation), group (ES vs. control), and IIV-I (high vs. low), such that only individuals who exhibited high IIV-I were negatively impacted by the ES manipulation.

IIV-I moderates the association between ES and EF, such that only individuals with high IIV-I exhibit vulnerability to the impact of ES. Thus, IIV-I may act as a marker of vulnerability to temporary EF depletion.

Attention and executive control in varsity athletes engaging in strategic and static sports

Examining non-sport-related cognitive tasks of attention and executive control in skilled athletes may provide insight into the acquisition of highly specific skills developed in experts as well as help identify successful performance in sport. Through a cross-sectional design, this study examined performance on aspects of attention and executive control among varsity athletes playing soccer (strategic sport) or track & field (static sport) using a computerized test of attention and executive control. Ninety-seven university athletes participating in soccer (n = 50) or track and field (n = 47) were included in the study. Domains of attention and executive control were examined using the Attention Network Test-Interactions (ANT-I). Mean reaction time (RT) and intra-individual variability (IIV) were compared between groups as measures of performance speed and performance stability respectively. Soccer players demonstrated overall faster RTs (p = 0.0499; ηp2 = .04) and higher response accuracy (p = .021, d = .48) on the ANT-I compared to track and field athletes. Faster RTs were observed for soccer players when presented with an alerting tone (p = .029, d = .45), valid orienting cue (p = .019, d = .49) and incongruent flanker (p = .031, d = .45). No significant group differences were observed in IIV (p = .083, d = .36). Athletes engaging in strategic sports (i.e., soccer) demonstrated faster performance under test conditions that required higher vigilance and conflict resolution. These findings suggest that engagement in strategic sports is associated with enhanced performance on non-sport-related cognitive tasks of attention and executive control.

Increased Intra-Individual Variability as a Marker of Executive Dysfunction in Generalized Anxiety Disorder

Recent studies suggest that individual difference in intra-individual variability (IIV) of reaction times is an important indicator of attentional executive control. However, there are few existing studies on the executive control of high trait-anxious individuals assessed by using reaction time variability. This study assessed whether executive functions are impaired among clinical and non-clinical trait-anxious individuals indicated by IIV. The cross-reliability and discriminative power of three IIV parameters (raw intra-individual standard deviation, SD; reaction time coefficient of variation, RTCV; and mean absolute deviation, MAD) were compared. Twenty-five non-clinical individuals with low trait anxiety (LTA), 31 non-clinical individuals with high trait anxiety (HTA), and 19 clinical patients diagnosed with generalized anxiety disorder (GAD) finished self-reported measures, an emotional spatial-cuing task, and a non-emotional arrow flanker task. In the emotional task, GAD patients had significantly slower response speed, lower accuracy, and greater IIV parameters than the LTA and HTA groups. In the non-emotional task, the GAD group exhibited poorer processing efficiency, greater SD and RTCV, and intact performance effectiveness. RTCV is suggested to be a better marker of executive dysfunction than SD and MAD due to its good discriminative power and reliability as well as less affected by reaction times.

Oral diadochokinetic rates across languages: Multilingual speakers comparison

BACKGROUND

It is unclear whether oral diadochokinetic rate (oral-DDK) performance is affected by different languages within a multilingual country.

AIMS

This study investigated the effects of age, sex, and stimulus type (real word in L1, L2 vs. non-word) on oral-DDK rates among healthy Malaysian-Malay speakers in order to establish language- and age-sensitive norms. The second aim was to compared the nonword 'pataka' oral-DDK rates produced by Malaysian-Malay speakers on currently available normative data for Hebrew speakers and Malaysian-Mandarin speakers.

METHODS & PROCEDURES

Oral-DDK performance of 90 participants (aged 20-77 years) using nonword ('pataka'), Malay real word ('patahkan'), and English real word ('buttercake') was audio recorded. The number of syllables produced in 8 seconds was calculated. Mixed analysis of variance (ANOVA) was conducted to examine the effects of stimulus type (nonword, Malay, and English real word), sex (male, female), age (younger, 20-40 years; middle, 41-60 years; older, ≥61 years), and their interactions on the oral-DDK rate. Data obtained were also compared with the raw data of Malaysian-Mandarin and Hebrew speakers from the previous studies.

OUTCOMES & RESULTS

A normative oral-DDK rate has been established for healthy Malaysian-Malay speakers. The oral-DDK rate was significantly affected by stimuli (p < 0.001). Malay real word showed the slowest rate, whereas there was no significant difference between English real word and nonword. The oral-DDK rate for Malay speakers was significantly higher than Mandarin and Hebrew speakers across stimuli (all p < 0.01). Interestingly, oral-DDK rates were not affected by age group for Malay speakers.

CONCLUSIONS & IMPLICATIONS

Stimuli type and language affect the oral-DDK rate, indicating that speech-language therapists should consider using language-specific norms when assessing multilingual speakers.

WHAT THIS PAPER ADDS

What is already known on the subject Age, sex, and language are factors that need to be considered when developing oral-DDK normative protocol. It is unclear whether oral-DDK performance is affected by different languages within a multilingual country. What this paper adds to existing knowledge No ageing effect across real word versus nonword on oral-DDK performance was observed among Malaysian-Malay speakers, contrasting with current available literature that speech movements slow down as we age. Additionally, Malaysian-Malay speakers have faster oral-DDK rates than Malaysian-Mandarin and Hebrew speakers across all stimuli. What are the potential or actual clinical implications of this work? Establishing normative data of different languages will enable speech-language therapists to select the appropriate reference dataset based on the language mastery of these multilingual speakers.

Cognitive throughput and working memory raw scores consistently differentiate resilient and vulnerable groups to sleep loss

STUDY OBJECTIVES

Substantial individual differences exist in cognitive deficits due to sleep restriction (SR) and total sleep deprivation (TSD), with various methods used to define such neurobehavioral differences. We comprehensively compared numerous methods for defining cognitive throughput and working memory resiliency and vulnerability.

METHODS

41 adults participated in a 13-day experiment: 2 baseline, 5 SR, 4 recovery, and one 36h TSD night. The Digit Symbol Substitution Test (DSST) and Digit Span Test (DS) were administered every 2h. Three approaches (Raw Score [average SR performance], Change from Baseline [average SR minus average baseline performance], and Variance [intraindividual variance of SR performance]), and six thresholds (±1 standard deviation, and the best/worst performing 12.5%, 20%, 25%, 33%, 50%) classified Resilient/Vulnerable groups. Kendall's tau-b correlations compared the group categorizations' concordance within and between DSST number correct and DS total number correct. Bias-corrected and accelerated bootstrapped t-tests compared group performance. .

RESULTS

The approaches generally did not categorize the same participants into Resilient/Vulnerable groups within or between measures. The Resilient groups categorized by the Raw Score approach had significantly better DSST and DS performance across all thresholds on all study days, while the Resilient groups categorized by the Change from Baseline approach had significantly better DSST and DS performance for several thresholds on most study days. By contrast, the Variance approach showed no significant DSST and DS performance group differences.

CONCLUSION

Various approaches to define cognitive throughput and working memory resilience/vulnerability to sleep loss are not synonymous. The Raw Score approach can be reliably used to differentiate resilient and vulnerable groups using DSST and DS performance during sleep loss.

Delineating visual, auditory and motor regions in the human brain with functional neuroimaging: a BrainMap-based meta-analytic synthesis

Most everyday behaviors and laboratory tasks rely on visual, auditory and/or motor-related processes. Yet, to date, there has been no large-scale quantitative synthesis of functional neuroimaging studies mapping the brain regions consistently recruited during such perceptuo-motor processing. We therefore performed three coordinate-based meta-analyses, sampling the results of neuroimaging experiments on visual (n = 114), auditory (n = 122), or motor-related (n = 251) processing, respectively, from the BrainMap database. Our analyses yielded both regions known to be recruited for basic perceptual or motor processes and additional regions in posterior frontal cortex. Comparing our results with data-driven network definitions based on resting-state functional connectivity revealed good overlap in expected regions but also showed that perceptual and motor task-related activations consistently involve additional frontal, cerebellar, and subcortical areas associated with "higher-order" cognitive functions, extending beyond what is captured when the brain is at "rest." Our resulting sets of domain-typical brain regions can be used by the neuroimaging community as robust functional definitions or masks of regions of interest when investigating brain correlates of perceptual or motor processes and their interplay with other mental functions such as cognitive control or affective processing. The maps are made publicly available via the ANIMA database.

The Impact of a Sustained Cognitive Engagement Intervention on Cognitive Variability: The Synapse Project

Background

Interest in maintaining one's cognitive ability and quality of life through older adulthood has greatly increased in recent years. However, research examining the effectiveness of cognitive engagement interventions on older adults is mixed and the mechanisms behind improving cognition in older age are unknown. It is possible that traditional measures of cognitive outcomes, such as average reaction time, may overlook potential benefits due to a lack of sensitivity in these measures. One alternative metric is intraindividual variability (IIV) in response speed (short-term variations in performance on reaction time tasks), which reflects fluctuations in attention and is a sensitive behavioral measure of neurological integrity that is predictive of future cognitive decline and impairment.

Objective

The current study aimed to investigate whether IIV was improved in older adults through productive cognitive engagement (i.e., acquisition of new skills) in comparison to receptive engagement (activities that rely upon existing knowledge).

Methods

Participants were 173 typically aging adults aged 60-90 years who were recruited to the Synapse Project and randomly allocated to a productive engagement activity (learning to quilt and/or conduct digital photography) or receptive engagement activity (socializing, or placebo cognitive tasks such as completing crosswords). Participants completed three flanker tasks at baseline and after completing the 14-week intervention program. IIV was calculated as the trial-to-trial variability in responding to congruent and incongruent trials in each task.

Results

Neither traditional intent-to-treat nor complier average causal effect modeling analyses showed any significant improvements in IIV for either intervention group. Further, Bayesian analyses showed that there was moderate evidence in favor of the null hypothesis.

Conclusion

An intensive cognitive activity intervention did not result in a reduction in IIV. We suggest that intervention programs may need to specifically engage cognitive domains associated with IIV (i.e., attention, executive control) for improvements to be observed. Additionally, other design factors such as using a longer duration and/or applying the intervention to atypically aging groups, such as those with mild cognitive impairment, may increase the likelihood of significantly reducing IIV via an intervention.

A Longitudinal Study of Allostatic Load in Later Life: The Role of Sex, Birth Cohorts, and Risk Accumulation

Are challenging life courses associated with more wear and tear on the biological level? This study investigates this question from a life-course perspective by examining the influence of life-course risk accumulation on allostatic load (AL), considering the role of sex and birth cohorts. Using biomarker data collected over three waves (2004, 2008, and 2012) of the English Longitudinal Study of Ageing ( N = 3,824) in a growth curve framework, AL trajectories over a period of 8 years are investigated. Our results illustrate that AL increases substantially in later life. Men have higher AL than women, but increases are similar for both sexes. Older cohorts have both higher levels and a steeper increase of AL over time. Higher risk accumulation over the life course goes hand in hand with higher AL levels and steeper trajectories, contributing to the body of evidence on cumulative (dis)advantage processes in later life.

Effectiveness of Intraindividual Variability in Detecting Subtle Cognitive Performance Deficits in Breast Cancer Patients

OBJECTIVES

The purpose of this study was to determine if intraindividual variability would be more sensitive than speed or accuracy in detecting subtle cancer-related cognitive disturbance.

METHODS

Data were from a previous study in which 60 breast cancer (BC) patients underwent neuropsychological assessment before commencement of chemotherapy and again following each chemotherapy cycle. Sixty healthy controls were tested at equivalent intervals. Hierarchical linear modeling was used to compare the BC and control groups in terms of accuracy, mean reaction time, and intraindividual variability in reaction time on a computerized continuous performance test with three conditions: a simple reaction time task, a "1-back" task, and a "2-back" task.

RESULTS

An increase in accuracy and response speed over sessions was noted on some tasks in the sample as a whole but there were no differences in these parameters between the BC patients and the controls on any condition. There was a significant group difference in change in intraindividual variability across sessions (i.e., a "group × session interaction"), albeit only on the most complex "2-back" task. Intraindividual variability declined in the control group (i.e., consistency improved with practice) but this practice effect was significantly attenuated in the BC patients. There was no main effect of group on the "2-back" task.

CONCLUSIONS

Results support our hypothesis that intraindividual variability is a more sensitive indicator of subtle cognitive disturbance than conventional speed or accuracy measures and may have potential in the assessment of mild cognitive impairment in patients with non-central nervous system cancers. (JINS, 2018, 24, 724-734).

Reliabilities of Intraindividual Variability Indicators with Autocorrelated Longitudinal Data: Implications for Longitudinal Study Designs

Intraindividual variability can be measured by the intraindividual standard deviation ([Formula: see text]), intraindividual variance ([Formula: see text]), estimated hth-order autocorrelation coefficient ([Formula: see text]), and mean square successive difference ([Formula: see text]). Unresolved issues exist in the research on reliabilities of intraindividual variability indicators: (1) previous research only studied conditions with 0 autocorrelations in the longitudinal responses; (2) the reliabilities of [Formula: see text] and [Formula: see text] have not been studied. The current study investigates reliabilities of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and the intraindividual mean, with autocorrelated longitudinal data. Reliability estimates of the indicators were obtained through Monte Carlo simulations. The impact of influential factors on reliabilities of the intraindividual variability indicators is summarized, and the reliabilities are compared across the indicators. Generally, all the studied indicators of intraindividual variability were more reliable with a more reliable measurement scale and more assessments. The reliabilities of [Formula: see text] were generally lower than those of [Formula: see text] and [Formula: see text], the reliabilities of [Formula: see text] were usually between those of [Formula: see text] and [Formula: see text] unless the scale reliability was large and/or the interindividual standard deviation in autocorrelation coefficients was large, and the reliabilities of the intraindividual mean were generally the highest. An R function is provided for planning longitudinal studies to ensure sufficient reliabilities of the intraindividual indicators are achieved.

Sequential Difficulty Effects in Cognitive and Sensorimotor Tasks: Insights from Arithmetic and Fitts Tasks

The present study tested sequential difficulty effects (SDEs) in arithmetic problem solving and Fitts’ aiming task for the same individuals. SDEs refer to poorer performance on current items following harder items relative to after easier items. Young and older adults accomplished an arithmetic task (i.e., finding the approximate products to two-digit multiplication problems) and a Fitts aiming task (i.e., performing rapid pointing movements to reach the finish areas). Current items were preceded by two easy or difficult items (i.e., in the repeated-precursor condition) or only one easy or difficult item (i.e., in the unrepeated-precursor condition). Participants’ performance revealed SDEs in both the arithmetic and the aiming tasks only when the difficulty level of the precursor items was repeated. Data also revealed comparable SDEs in both age groups during the arithmetic task but SDEs only in older adults while participants accomplished the aiming task. These findings have a number of implications for our understanding of mechanisms underlying SDEs and age-related differences in SDEs, as they suggest that SDEs involve both domain-general and domain-specific mechanisms that are differentially influenced by aging.

Both Reaction Time and Accuracy Measures of Intraindividual Variability Predict Cognitive Performance in Alzheimer's Disease

Dementia researchers around the world prioritize the urgent need for sensitive measurement tools that can detect cognitive and functional change at the earliest stages of Alzheimer's disease (AD). Sensitive indicators of underlying neural pathology assist in the early detection of cognitive change and are thus important for the evaluation of early-intervention clinical trials. One method that may be particularly well-suited to help achieve this goal involves the quantification of intraindividual variability (IIV) in cognitive performance. The current study aimed to directly compare two methods of estimating IIV (fluctuations in accuracy-based scores vs. those in latency-based scores) to predict cognitive performance in AD. Specifically, we directly compared the relative sensitivity of reaction time (RT)-and accuracy-based estimates of IIV to cognitive compromise. The novelty of the present study, however, centered on the patients we tested [a group of patients with Alzheimer's disease (AD)] and the outcome measures we used (a measure of general cognitive function and a measure of episodic memory function). Hence, we compared intraindividual standard deviations (iSDs) from two RT tasks and three accuracy-based memory tasks in patients with possible or probable Alzheimer's dementia (n = 23) and matched healthy controls (n = 25). The main analyses modeled the relative contributions of RT vs. accuracy-based measures of IIV toward the prediction of performance on measures of (a) overall cognitive functioning, and (b) episodic memory functioning. Results indicated that RT-based IIV measures are superior predictors of neurocognitive impairment (as indexed by overall cognitive and memory performance) than accuracy-based IIV measures, even after adjusting for the timescale of measurement. However, one accuracy-based IIV measure (derived from a recognition memory test) also differentiated patients with AD from controls, and significantly predicted episodic memory performance. The findings suggest that both RT- and accuracy-based IIV measures may be useful indicators of underlying neuropathology. The present study therefore contributes toward an understanding of the relative utility of RT- and accuracy-based IIV measures in detecting neurocognitive impairment in older adults, and also advances the empirical evaluation of sensitive markers of cognitive change in patients with AD.

Variability in the Precision of Children's Spatial Working Memory

Cognitive modeling studies in adults have established that visual working memory (WM) capacity depends on the representational precision, as well as its variability from moment to moment. By contrast, visuospatial WM performance in children has been typically indexed by response accuracy—a binary measure that provides less information about precision with which items are stored. Here, we aimed at identifying whether and how children’s WM performance depends on the spatial precision and its variability over time in real-world contexts. Using smartphones, 110 Grade 3 and Grade 4 students performed a spatial WM updating task three times a day in school and at home for four weeks. Measures of spatial precision (i.e., Euclidean distance between presented and reported location) were used for hierarchical modeling to estimate variability of spatial precision across different time scales. Results demonstrated considerable within-person variability in spatial precision across items within trials, from trial to trial and from occasion to occasion within days and from day to day. In particular, item-to-item variability was systematically increased with memory load and lowered with higher grade. Further, children with higher precision variability across items scored lower in measures of fluid intelligence. These findings emphasize the important role of transient changes in spatial precision for the development of WM.

Within-Individual Variability: An Index for Subtle Change in Neurocognition in Mild Cognitive Impairment

BACKGROUND

The transition from mild cognitive impairment (MCI) to Alzheimer's disease is characterized by a decline in cognitive performance in many domains. Cognitive performance profiles in MCI are heterogeneous, however, and additional insights into markers of incipient dementia are needed. Typically, studies focus on average or mean performance, but ignore consistency of performance across domains. WIV (within-individual variability) provides an index of this consistency and is a potential marker of cognitive decline.

OBJECTIVE

To use neurocognitive data from the Alzheimer's Disease Neuroimaging Initiative cohort to measure neurocognitive variability.

METHODS

The utility of WIV was measured, in addition to global neurocognitive performance (GNP), for identifying AD and MCI. In addition, the association between changes in neurocognitive variability and diagnostic transition over 12 months was measured.

RESULTS

As expected, variability was higher in AD and MCI as compared to healthy controls; GNP was lower in both groups as compared to healthy subjects. Global neurocognitive performance alone best distinguished those with dementia from healthy older adults. Yet, for individuals with MCI, including variability along with GNP improved diagnostic classification. Variability was higher at baseline in individuals transitioning from MCI to AD over a 12-month period.

CONCLUSION

We conclude that variability offers complementary information about neurocognitive performance in dementia, particularly in individuals with MCI, and may provide beneficial information about disease transition.

Biomarkers, Health, Lifestyle, and Demographic Variables as Correlates of Reaction Time Performance in Early, Middle, and Late Adulthood

We aimed to identify demographic, health, and biomarker correlates of reaction time performance and to determine whether biomarkers explained age differences in reaction time performance. The sample comprised three representative cohorts aged 20–24, 40–44, and 60–64 years, including a total of 7,485 participants. Reaction time measures of intraindividual variability and latency were used. The measure of intraindividual variability used was independent of mean reaction time. Older adults were more variable than younger adults in choice reaction time performance but not simple reaction time performance. The most important correlates of reaction time performance after gender and education were biological markers such as forced expiratory volume at one second, grip strength, and vision. Few measures of physical or mental health or lifestyle were associated with poorer performance on reaction time measures. Biomarkers explained the majority of age-related variance in simple reaction time and a large proportion of variance in choice reaction time. We conclude that for the ages studied, biomarkers are more important than health factors for explaining age differences in reaction time performance.

The effect of age and microstructural white matter integrity on lap time variation and fast-paced walking speed

Macrostructural white matter damage (WMD) is associated with less uniform and slower walking in older adults. The effect of age and subclinical microstructural WM degeneration (a potentially earlier phase of WM ischemic damage) on walking patterns and speed is less clear. This study examines the effect of age on the associations of regional microstructural WM integrity with walking variability and speed, independent of macrostructural WMD. This study involved 493 participants (n = 51 young; n = 209 young-old; n = 233 old-old) from the Baltimore Longitudinal Study of Aging. All completed a 400-meter walk test and underwent a concurrent brain MRI with diffusion tensor imaging. Microstructural WM integrity was measured as fractional anisotropy (FA). Walking variability was measured as trend-adjusted variation in time over ten 40-meter laps (lap time variation, LTV). Fast-paced walking speed was assessed as mean lap time (MLT). Multiple linear regression models of FA predicting LTV and MLT were adjusted for age, sex, height, weight, and WM hyperintensities. Independent of WM hyperintensities, lower FA in the body of the corpus callosum was associated with higher LTV and longer MLT only in the young-old. Lower FA in superior longitudinal, inferior fronto-occipital, and uncinate fasciculi, the anterior limb of the internal capsule, and the anterior corona radiate was associated with longer MLT only in the young-old. While macrostructural WMD is known to predict more variable and slower walking in older adults, microstructural WM disruption is independently associated with more variable and slower fast-paced walking only in the young-old. Disrupted regional WM integrity may be a subclinical contributor to abnormal walking at an earlier phase of aging.

Age-Related Intraindividual Performance Variability with Practice

Fluctuations in cognitive task performance in older individuals have been reported. To examine intraindividual variability as a function of practice, 34 younger and 34 older female participants, aged 20–30 years and 70–82 years, respectively, performed a reading span task 16 times over four sessions. Each individual's recall accuracy was analyzed over the practice trials. It was found that intraindividual variability occurred more frequently in older than younger individuals, and that fluctuations were more frequent in mid to later trials of practice. These findings were interpreted within a resource theory framework as evidence for age-related inefficient cognitive processing with practice.

Connecting the Many Levels and Facets of Cognitive Aging

Basic cognitive mechanisms, such as the abilities to briefly maintain, focus, and process information, decline with age. Related fields of cognitive aging research have been advancing rapidly, but mostly independently, at the biological, information processing, and behavioral levels. To facilitate integration, this article reviews research on cognitive aging at the different levels, and describes a recent integrative theory postulating that aging-related deficiencies in neurotransmission cause increased noise in information processing and less distinctive cortical representation, which in turn lead to cognitive deficits. Aging-related attenuation of catecholaminergic modulation can be modeled by lowering a neural network parameter to reduce the signal-to-noise ratio of information processing. The performance of such models is consistent with benchmark phenomena observed in humans, ranging from age differences in learning rate, asymptotic performance, and interference susceptibility to intra- and interindividual variability and ability dedifferentiation. Although the details of the conjectured sequence of effects linking neuromodulation to cognitive aging deficits await further empirical validation, cross-level theorizing of the kind illustrated here could foster the coevolution of related fields through cross-level data synthesis and hypothesis testing.

Influence of divergent and convergent thinking on visuomotor adaptation in young and older adults

Visuomotor adaptation declines in older age. This has been attributed to cognitive impairments. One relevant cognitive function could be creativity, since creativity is implicated as mediator of early learning. The present study therefore evaluates whether two aspects of creativity, divergent and convergent thinking, are differentially involved in the age-dependent decline of visuomotor adaptation. In 25 young and 24 older volunteers, divergent thinking was assessed by the alternative-uses-task (AUT), convergent thinking by the Intelligenz-Struktur-Test-2000 (IST), and sensorimotor-adaptation by a pointing task with 60° rotated visual feedback. Young participants outperformed older participants in all three tasks. AUT scores were positively associated with young but not older participants' adaptive performance, whereas IST scores were negatively associated with older but not young participants' adaptive performance. This pattern of findings could be attributed to a consistent relationship between AUT, IST and adaptation; taking this into account, adaptation deficits of older participants were no longer significant. We conclude that divergent thinking supports workaround-strategies during adaptation, but doesn't influence visuomotor recalibration. Furthermore, the decay of divergent thinking in older adults may explain most of age-related decline of adaptive strategies. When the age-related decay of divergent thinking coincides with well-preserved convergent thinking, adaptation suffers most.

Intra-individual lap time variation of the 400-m walk, an early mobility indicator of executive function decline in high-functioning older adults?

Higher intra-individual lap time variation (LTV) of the 400-m walk is cross-sectionally associated with poorer attention in older adults. Whether higher LTV predicts decline in executive function and whether the relationship is accounted for by slower walking remain unanswered. The main objective of this study was to examine the relationship between baseline LTV and longitudinal change in executive function. We used data from 347 participants aged 60 years and older (50.7% female) from the Baltimore Longitudinal Study of Aging. Longitudinal assessments of executive function were conducted between 2007 and 2013, including attention (Trails A, Digit Span Forward Test), cognitive flexibility and set shifting (Trails B, Delta TMT: Trials B minus Trials A), visuoperceptual speed (Digit Symbol Substitution Test), and working memory (Digit Span Backward Test). LTV and mean lap time (MLT) were obtained from the 400-m walk test concurrent with the baseline executive function assessment. LTV was computed as variability of lap time across ten 40-m laps based on individual trajectories. A linear mixed-effects model was used to examine LTV in relation to changes in executive function, adjusted for age, sex, education, and MLT. Higher LTV was associated with greater decline in performance on Trails B (β = 4.322, p < 0.001) and delta TMT (β = 4.230, p < 0.001), independent of covariates. Findings remained largely unchanged after further adjustment for MLT. LTV was not associated with changes in other executive function measures (all p > 0.05). In high-functioning older adults, higher LTV in the 400-m walk predicts executive function decline involving cognitive flexibility and set shifting over a long period of time. High LTV may be an early indicator of executive function decline independent of MLT.

Daily Fluctuations in Everyday Cognition: Is It Meaningful?

OBJECTIVE

This study examined whether there are daily fluctuations in everyday cognition that are consistent with daily fluctuations often observed in traditional measures of basic cognitive abilities.

METHOD

Two hundred six independently living older adults (age range = 60-91 years) were asked to complete a computerized cognitive battery over eight occasions within a 2- to 3-week period.

RESULTS

Using multilevel model, significant within-person variability was observed across the Daily Everyday Cognition Assessment (DECA; 46%), with 54% between-person variability. At each occasion, better performance on the DECA was significantly associated with better performance on simple reaction time ( p < .01) and memory (Auditory Verbal Learning Task, p < .01) even after accounting for time, age, education, and performance on other cognitive measures.

CONCLUSION

These findings demonstrate that within-person performance fluctuations can be observed for everyday cognition tasks, and these fluctuations are consistent with daily changes in basic cognitive abilities.

Lap time variation and executive function in older adults: the Baltimore Longitudinal Study of Aging

BACKGROUND

poor cognitive and motor performance predicts neurological dysfunction. Variable performance may be a subclinical indicator of emerging neurological problems.

OBJECTIVE

examine the cross-sectional association between a clinically accessible measure of variable walking and executive function.

METHODS

older adults aged 60 or older from the Baltimore Longitudinal Study of Aging (n = 811) with data on the 400-m walk test and cognition. Based on ten 40-m laps, we calculated mean lap time (MLT) and variation in time across ten 40-m laps (lap time variation, LTV). Executive function tests assessed attention and short-term memory (digit span forward and backward), psychomotor speed [Trail Making Test (TMT) part A] and multicomponent tasks requiring cognitive flexibility [TMT part B, part B-A (Delta TMT) and digit symbol substitution test (DSST)]. Multivariate linear regression analysis examined the cross-sectional association between LTV and executive function, adjusted for MLT, age, sex and education, as well as the LTV × MLT interaction.

RESULTS

the LTV was univariately associated with all executive function tests except digit span (P < 0.001); after adjustment, the association with TMT part A remained (standardised β = 0.142, P = 0.002). There was an interaction between MLT and LTV; among fast walkers, greater LTV was associated with a greater Delta TMT (β for LTV × MLT = -1.121, P = 0.016) after adjustment.

CONCLUSION

at any walking speed, greater LTV is associated with psychomotor slowing. Among persons with faster walking speed, variation is associated with worse performance on a complex measure of cognitive flexibility. A simple measure of variability in walking time is independently associated with psychomotor slowing.

From Noise to Signal: The Age and Social Patterning of Intra-Individual Variability in Late-Life Health

OBJECTIVES

Despite a long tradition of attending to issues of intra-individual variability in the gerontological literature, large-scale panel studies on late-life health disparities have primarily relied on average health trajectories, relegating intra-individual variability over time to random error terms, or "noise." This article reintegrates the systematic study of intra-individual variability back into standard growth curve modeling and investigates the age and social patterning of intra-individual variability in health trajectories.

METHOD

Using panel data from the Health and Retirement Study, we estimate multilevel growth curves of functional limitations and cognitive impairment and examine whether intra-individual variability in these two health outcomes varies by age, gender, race/ethnicity, and socioeconomic status, using level-1 residuals extracted from the adjusted growth curve models.

RESULTS

For both outcomes, intra-individual variability increases with age. Racial/ethnic minorities and individuals with lower socioeconomic status tend to have greater intra-individual variability in health. Relying exclusively on average health trajectories may have masked important "signals" of life course health inequality.

DISCUSSION

The findings contribute to scientific understanding of the source of heterogeneity in late-life health and highlight the need to further investigate specific life course mechanisms that generate the social patterning of intra-individual variability in health status.

Does initial performance variability predict dual-task optimization with practice in younger and older adults?

BACKGROUND/STUDY CONTEXT: The variability associated with reaction time (RT) is sometimes considered as a proxy for inefficient neural processing, particularly in old age and complex situations relying upon executive control functions. Here, it is examined whether the amount of variability exhibited early in practice can predict the amount of improvement with later practice in dual-task performance, and whether the predictive power of variability varies between younger and older adults.

METHODS

To investigate the relationship between variability and practice-related improvement, RT mean and variability data are used, obtained from an experiment in which younger and older adults performed two tasks in single-task and dual-task conditions across seven practice sessions. These RT and variability data were related to the single-task and dual-task practice benefits. These benefits were computed as follows: dual-task/single-task RTs at the beginning of practice minus dual-task/single-task RTs at the end of practice.

RESULTS

In both age groups, dual-task processing was speeded up with practice and variability associated with the means was reduced. Most important, independent of mean RTs, variability allowed predicting dual-task practice benefit in both age groups under specific conditions.

CONCLUSION

These findings suggest that the relationship between performance variability and executive control functions under some specific conditions. Implications of these results for models of practiced dual tasks are discussed.

Intra-individual variability in women with breast cancer

Studies assessing cognitive functioning in women treated for breast cancer have used primarily standardized neuropsychological tests and examined accuracy and/or reaction time as outcome measures: they have been inconsistent in identifying the cognitive domains affected and the severity of deficits. In other contexts of neural development and disorders, measures of Intra-individual variability (IIV) have proven useful in identifying subtleties in performance deficits that are not captured by measures of central tendency. This article presents proof of concept that assessing IIV may also increase understanding of the cognitive effects of cancer treatment. We analyzed mean accuracy and reaction time, as well as IIV from 65 women with breast cancer and 28 age and education matched controls who performed the Conner's Continuous Performance Test, a "Go-NoGo" task. Although there were no significant differences between groups using measures of central tendency, there was a group × inter-stimulus interval (ISI) interaction for IIV Dispersion (p < .001). Patient Dispersion was more variable at shorter ISI than controls and less variable at long ISI, suggesting greater sensitivity to presentation speed. Interpretation of IIV differences requires further investigation. Our results suggest that future studies would benefit from designs that allow analysis of IIV measures in studies assessing cognition in cancer survivors.

Intra-individual Variability as a Measure of Information Processing Difficulties in Multiple Sclerosis

Deficits in information processing speed are among the most commonly reported impairments in multiple sclerosis (MS) and are generally assessed by evaluating mean-level performance on time-limited tests. However, this approach to assessing performance ignores potential within-subject differences in MS patients that may be useful for characterizing cognitive difficulties in MS. An alternative method of measuring performance is by examining the degree of within-subject variability, termed intra-individual variability (IIV). Intra-individual variability provides information about the characteristics of a person's performance over time and may provide novel information about cognitive functioning in MS. This study examined IIV in performance on the Computerized Test of Information Processing (CTIP) using two within-subject variability methods: individual standard deviation and coefficient of variation. Eighteen females with relapsing-remitting MS and 18 healthy female controls completed the CTIP. Consistent with previous research, MS patients demonstrated slower overall mean performance on the CTIP compared with controls, with patients becoming increasingly slower than controls as cognitive demands increased across the tasks. Furthermore, MS patients demonstrated greater IIV as measured by individual standard deviations on all subtests of the CTIP, even with mean-level group differences as well as practice and learning effects controlled. These between-group differences were not found when the coefficient of variation, a more coarse measure of within-subject variability, was used. Intra-individual variability was also found to be a better predictor of neurologic status than mean-level performance. These results suggest that IIV may provide unique insight into cognitive functioning in MS.

Social possible selves, self-regulation, and social goal progress in older adulthood

Lifespan development involves setting and pursuing self-guided goals. This study examines how in the social domain, possible selves, a future-oriented self-concept, and self-regulation, including self-regulatory beliefs and intraindividual variability in self-regulatory behavior, relate to differences in overall daily social goal progress. An online older-adult sample worked towards a self-defined meaningful social goal over 100 days. Multilevel analysis showed that participants with social possible selves made higher overall daily goal progress, especially those with both hoped-for and feared possible selves, than those with possible selves in nonsocial domains. Self-regulatory beliefs were positively whereas variability was negatively associated with overall daily goal progress. The findings suggest that possible selves, in combination with two distinct self-regulatory constructs, significantly guide social goal progress.

A multidimensional view of out-of-home behaviors in cognitively unimpaired older adults: examining differential effects of socio-demographic, cognitive, and health-related predictors

Previous studies on predictors of out-of-home behavior (OOHB) have often neglected the multidimensional nature of this construct. The present study distinguished between two levels of analyzing OOHB: out-of-home mobility seen as single behavioral units (e.g., number of places visited, action range, and walking) versus OOHBs seen as engagement in integrated, larger activity units (e.g., cognitively and physically demanding activities). We examined whether a differential relationship between these levels of OOHBs with established predictors of OOHBs, i.e., socio-demographic variables, cognitive abilities, physical functioning, and depression, exists. A sample of 100 cognitively healthy, community-dwelling adults with a mean age of 70.8 years underwent a multi-method OOHB assessment using GPS- (out-of-home mobility) and questionnaire-based (out-of-home activity engagement) measures. Predictors were assessed based on internationally implemented procedures. Regression analyses showed that walking-based mobility and engagement in physical activities could be predicted by physical functioning, whereas most effects of socio-demographic variables, such as age and gender, and of depression on OOHBs were negligible. At the bivariate level, episodic memory was related to action range, global mobility, and to cognitively demanding activity engagement, but not to walking, whereas executive function was related with physically demanding activity engagement only. However, some of these connections became weaker in the full predictor model. Findings support the notion that it is necessary to assess OOHB as a multiple-indicator construct.

Neurocognitive performance stability in a multiplex multigenerational study of schizophrenia

Certain cognitive measures are heritable and differentiate individuals at risk for schizophrenia from unaffected family members and healthy comparison subjects. These deficits in neurocognitive performance in patients with schizophrenia appear stable in the short-term. However, the duration of most, but not all, longitudinal studies is modest and the majority have relied on traditional average performance measures to examine stability. Using a computerized neurocognitive battery (CNB), we assessed mean performance (accuracy and speed) and intra-individual variability (IIV) in a longitudinal study aimed to examine neurocognitive stability in European-American multiplex families with schizophrenia. Thirty-four patients with schizophrenia, 65 unaffected relatives, and 45 healthy comparison subjects completed the same computerized neurocognitive assessment over approximately 5 years. Measures of mean performance showed that patients had stable accuracy performance but were slower in many neurocognitive domains over time as compared with unaffected family members and healthy subjects. Furthermore, patients and family members showed dissociable patterns of change in IIV for speed across cognitive domains: compared with controls, patients showed higher across-task IIV in performance compared with family members, who showed lower across-task IIV. Patients showed an increase in IIV over time, whereas family members showed a decrease. These findings suggest that measures of mean performance and IIV of speed during a CNB may provide useful information about the genetic susceptibility in schizophrenia.

Cognitive Inconsistency and Practice-Related Learning in Older Adults

The current study examined predictors of individual differences in the magnitude of practice-related improvements achieved by 87 older adults (mean_age 63.52 years) over 18-weeks of cognitive practice. Cognitive inconsistency in both baseline trial-to-trial reaction times and week-to-week accuracy scores was included as predictors of practice-related gains in two measures of processing speed. Conditional growth models revealed that both reaction time and accuracy level and rate-of-change in functioning were related to inconsistency, even after controlling for mean-level, but that increased inconsistency was negatively associated with accuracy versus positively associated with reaction time improvement. Cognitive inconsistency may signal dysregulation in the ability to control cognitive performance or may be indicative of adaptive attempts at functioning.

Keeping it steady: older adults perform more consistently on cognitive tasks than younger adults

People often attribute poor performance to having bad days. Given that cognitive aging leads to lower average levels of performance and more moment-to-moment variability, one might expect that older adults should show greater day-to-day variability and be more likely to experience bad days than younger adults. However, both researchers and ordinary people typically sample only one performance per day for a given activity. Hence, the empirical basis for concluding that cognitive performance does substantially vary from day to day is inadequate. On the basis of data from 101 younger and 103 older adults who completed nine cognitive tasks in 100 daily sessions, we show that the contributions of systematic day-to-day variability to overall observed variability are reliable but small. Thus, the impression of good versus bad days is largely due to performance fluctuations at faster timescales. Despite having lower average levels of performance, older adults showed more consistent levels of performance across days.

Intra-individual variability in information processing speed reflects white matter microstructure in multiple sclerosis

Slowed information processing speed is commonly reported in persons with multiple sclerosis (MS), and is typically investigated using clinical neuropsychological tests, which provide sensitive indices of mean-level information processing speed. However, recent studies have demonstrated that within-person variability or intra-individual variability (IIV) in information processing speed may be a more sensitive indicator of neurologic status than mean-level performance on clinical tests. We evaluated the neural basis of increased IIV in mildly affected relapsing–remitting MS patients by characterizing the relation between IIV (controlling for mean-level performance) and white matter integrity using diffusion tensor imaging (DTI). Twenty women with relapsing–remitting MS and 20 matched control participants completed the Computerized Test of Information Processing (CTIP), from which both mean response time and IIV were calculated. Other clinical measures of information processing speed were also collected. Relations between IIV on the CTIP and DTI metrics of white matter microstructure were evaluated using tract-based spatial statistics. We observed slower and more variable responses on the CTIP in MS patients relative to controls. Significant relations between white matter microstructure and IIV were observed for MS patients. Increased IIV was associated with reduced integrity in more white matter tracts than was slowed information processing speed as measured by either mean CTIP response time or other neuropsychological test scores. Thus, despite the common use of mean-level performance as an index of cognitive dysfunction in MS, IIV may be more sensitive to the overall burden of white matter disease at the microstructural level. Furthermore, our study highlights the potential value of considering within-person fluctuations, in addition to mean-level performance, for uncovering brain–behavior relationships in neurologic disorders with widespread white matter pathology.

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Intra-individual variability (IIV) predicts neurologic status in multiple sclerosis (MS).

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Diffusion tensor imaging (DTI) was used to study the neural correlates of IIV in MS.

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IIV was significantly related to DTI metrics in many white matter regions.

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Compared to mean response speed, IIV may be more sensitive to disease burden in MS.

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Evaluating IIV may be important for characterizing brain–behavior relationships.

Intra-individual variability in gait and in cognitive performance are not related in the elderly

As humans age, the amount of intra-individual variability (IIV) present in both their gait and their cognitive performance tends to increase. Both gait and cognitive IIV are associated with attentional control and with cerebrovascular disease, suggesting that the IIV in gait and cognitive function should be strongly correlated in the elderly. In this study temporal gait variability was determined from a 60-second period of walking. Cognitive variability was determined from two decision-time tasks assessing inhibition. Despite the presence of substantial amounts of gait and cognitive IIV in 71 elderly individuals, there were no significant correlations between measures of cognitive and gait IIV, suggesting that different factors drive IIV in the motor and cognitive performance of older individuals. These results are not consistent with the common cause theory of aging, which predicts that cognitive and sensorimotor performance should show related declines due to age-related disruption of a common neurological substrate.

A Monte Carlo simulation study of the reliability of intraindividual variability

Recent research has seen intraindividual variability become a useful technique to incorporate trial-to-trial variability into many types of psychological studies. Intraindividual variability, as measured by individual standard deviations (ISDs), has shown unique prediction to several types of positive and negative outcomes (Ram, Rabbit, Stollery, & Nesselroade, 2005). One unanswered question regarding measuring intraindividual variability is its reliability and the conditions under which optimal reliability is achieved. Monte Carlo simulation studies were conducted to determine the reliability of the ISD as compared with the intraindividual mean. The results indicate that ISDs generally have poor reliability and are sensitive to insufficient measurement occasions, poor test reliability, and unfavorable amounts and distributions of variability in the population. Secondary analysis of psychological data shows that use of individual standard deviations in unfavorable conditions leads to a marked reduction in statistical power, although careful adherence to underlying statistical assumptions allows their use as a basic research tool.

Neurocognitive speed and inconsistency in Parkinson's disease with and without incipient dementia: an 18-month prospective cohort study

We examined two-wave longitudinal changes in two indicators of neurocognitive speed (i.e., mean rate, intraindividual variability) using one simple and three complex reaction time tasks. Participants included idiopathic Parkinson's disease (PD) patients, with and without incipient dementia, and normal controls. At baseline, there were 45 patients (26 men, 19 women) with idiopathic PD who ranged from 65 to 84 years (M = 71.3; SD = 4.5) and 47 matched controls (27 men, 20 women) who ranged from 65 to 84 years (M = 71.4; SD = 4.9). The 18-month longitudinal sample comprised of 74 returning participants (43 controls; 31 PD patients) who had no cognitive impairment or dementia at both waves. Ten of the 31 PD patients returning for Time 3 had dementia or cognitive impairment. These constituted the PD with incipient dementia (PDID) group. Repeated measures analyses of variance showed that the PD and PDID groups were slower over time on the reaction time tasks, whereas the controls improved their performance over time on all tasks. Inconsistency distinguished the two clinical groups (i.e., the PDID group but not the PD group became more inconsistent over time). Changes in neurocognitive speed and inconsistency may be valid clinical markers of PDID.

Variability in performance: identifying early signs of future cognitive impairment

OBJECTIVE

The current study examined whether year-to-year variability in cognitive performance differ between individuals cognitively unimpaired and individuals who subsequently develop dementia.

METHOD

Analyses included a case-control sample of Baltimore Longitudinal Study of Aging (BLSA; mean [M] age = 69.90, standard deviation [SD] = 8.92) participants. One hundred and 35 clinically diagnosed demented participants were matched with 135 nondemented participants based on age at initial testing and sex. Cognitive performance was examined using measures of memory, executive function, attention, language, and global mental status performance. Cognitive performance was examined from baseline to 5 years before cognitive impairment (M, assessments = 3.03, SD = 2.80).

RESULTS

As compared with unimpaired individuals, individuals diagnosed with dementia had greater variability on measures of attention, executive function, language, and semantic memory at least 5 years before the estimated onset of cognitive impairment, which may be indicative of maladaptive cognitive functioning. The dementia cases, however, had less variability on visual memory than the unimpaired group, which may suggest that these cases had more difficulty learning.

CONCLUSIONS

These results demonstrate that performance variability indexed over annual or biennial visits may be useful in identifying early signs of subsequent cognitive impairment.

Effect of age on variability in the production of text-based global inferences

As we age, our differences in cognitive skills become more visible, an effect especially true for memory and problem solving skills (i.e., fluid intelligence). However, by contrast with fluid intelligence, few studies have examined variability in measures that rely on one's world knowledge (i.e., crystallized intelligence). The current study investigated whether age increased the variability in text based global inference generation--a measure of crystallized intelligence. Global inference generation requires the integration of textual information and world knowledge and can be expressed as a gist or lesson. Variability in generating two global inferences for a single text was examined in young-old (62 to 69 years), middle-old (70 to 76 years) and old-old (77 to 94 years) adults. The older two groups showed greater variability, with the middle elderly group being most variable. These findings suggest that variability may be a characteristic of both fluid and crystallized intelligence in aging.

Psychometric properties of within-person across-session variability in accuracy of cognitive performance

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.

Dynamic links between memory and functional limitations in old age: longitudinal evidence for age-based structural dynamics from the AHEAD study

This study examined competing substantive hypotheses about dynamic (i.e., time-ordered) links between memory and functional limitations in old age. We applied the Bivariate Dual Change Score Model to 13-year longitudinal data from the Asset and Health Dynamics Among the Oldest Old Study (AHEAD; N = 6,990; ages 70 - 95). Results revealed that better memory predicted shallower increases in functional limitations. Little evidence was found for the opposite direction that functional limitations predict ensuing changes in memory. Spline models indicated that dynamic associations between memory and functional limitations were substantively similar between participants aged 70-79 and those aged 80-95. Potential covariates (gender, education, health conditions, and depressive symptoms) did not account for these differential lead-lag associations. Applying a multivariate approach, our results suggest that late-life developments in two key components of successful aging are intrinsically interrelated. Our discussion focuses on possible mechanisms why cognitive functioning may serve as a source of age-related changes in health both among the young-old and the old-old.

Noise and complexity in human postural control: interpreting the different estimations of entropy

Background

Over the last two decades, various measures of entropy have been used to examine the complexity of human postural control. In general, entropy measures provide information regarding the health, stability and adaptability of the postural system that is not captured when using more traditional analytical techniques. The purpose of this study was to examine how noise, sampling frequency and time series length influence various measures of entropy when applied to human center of pressure (CoP) data, as well as in synthetic signals with known properties. Such a comparison is necessary to interpret data between and within studies that use different entropy measures, equipment, sampling frequencies or data collection durations.

Methods and Findings

The complexity of synthetic signals with known properties and standing CoP data was calculated using Approximate Entropy (ApEn), Sample Entropy (SampEn) and Recurrence Quantification Analysis Entropy (RQAEn). All signals were examined at varying sampling frequencies and with varying amounts of added noise. Additionally, an increment time series of the original CoP data was examined to remove long-range correlations. Of the three measures examined, ApEn was the least robust to sampling frequency and noise manipulations. Additionally, increased noise led to an increase in SampEn, but a decrease in RQAEn. Thus, noise can yield inconsistent results between the various entropy measures. Finally, the differences between the entropy measures were minimized in the increment CoP data, suggesting that long-range correlations should be removed from CoP data prior to calculating entropy.

Conclusions

The various algorithms typically used to quantify the complexity (entropy) of CoP may yield very different results, particularly when sampling frequency and noise are different. The results of this study are discussed within the context of the neural noise and loss of complexity hypotheses.

Predisability and gait patterns in older adults

Presence of performance inconsistency during repeated assessments of gait may reflect underlying subclinical disease, and help shed light on the earliest stages of disablement. We studied inter-session fluctuations on three selected gait measures (velocity, stride length, and stride length variability) during normal pace walking as well as during a cognitively demanding 'walking while talking' condition using a repeated measurement burst design (six sessions within a 2-week period) in 71 nondisabled and nondemented community residing older adults, 40 with predisability (does activities of daily living unassisted but with difficulty). Subjects with predisability had slower gait velocity and shorter stride length on both the normal and walking while talking conditions at baseline compared to nondisabled subjects. However, there was no significant pattern of fluctuations across the six sessions on the three selected gait variables comparing the two groups during normal walking as well as on the walking while talking conditions. Our findings support consistency of gait measurements during the earliest stages of disability.

Aging and cognition

As we grow older, we gain knowledge and experience greater emotional balance, but we also experience memory loss and difficulties in learning new associations. Which cognitive abilities decline, remain stable or improve with age depends on the health of the brain and body as well as on what skills are practiced or challenged in everyday life. Recent research provides a growing understanding of the relationship between physical and cognitive changes across the life span and reveals ways to increase mental sharpness and avoid cognitive decline. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

The relationship between everyday problem solving and inconsistency in reaction time in older adults

The purpose of the present study was to investigate whether inconsistency in reaction time (RT) is predictive of older adults' ability to solve everyday problems. A sample of 304 community dwelling non-demented older adults, ranging in age from 62 to 92, completed a measure of everyday problem solving, the Everyday Problems Test (EPT). Inconsistency in latencies across trials was assessed on four RT tasks. Performance on the EPT was found to vary according to age and cognitive status. Both mean latencies and inconsistency were significantly associated with EPT performance, such that slower and more inconsistent RTs were associated with poorer everyday problem solving abilities. Even after accounting for age, education, and mean level of performance, inconsistency in reaction time continued to account for a significant proportion of the variance in EPT scores. These findings suggest that indicators of inconsistency in RT may be of functional relevance.