Intra-individual Performance Variability Research Articles

The delta concept does not effectively normalise exercise responses to exhaustive interval training

ObjectivesThis study was designed to quantify inter- and intra-individual variability in performance, physiological, and perceptual responses to high-intensity interval training prescribed using the percentage of delta (%Δ) method, in which the gas exchange threshold and maximal oxygen uptake (V̇O2max) are taken into account to normalise relative exercise intensity. DesignRepeated-measures, within-subjects design with mixed-effects modelling. MethodsEighteen male and four female cyclists (age: 36 ± 12 years, height: 178 ± 10 cm, body mass: 75.2 ± 13.7 kg, V̇O2max: 51.6 ± 5.3 ml·kg−1·min−1) undertook an incremental test to exhaustion to determine the gas exchange threshold and V̇O2max as prescription benchmarks. On separate occasions, participants then completed four high-intensity interval training sessions of identical intensity (70 %Δ) and format (4-min on, 2-min off); all performed to exhaustion. Acute high-intensity interval training responses were modelled with participant as a random effect to provide estimates of inter- and intra-individual variability. ResultsGreater variability was generally observed at the between- compared with the within-individual level, ranging from 50 % to 89 % and from 11 % to 50 % of the total variability, respectively. For the group mean time to exhaustion of 20.3 min, inter- and intra-individual standard deviations reached 9.3 min (coefficient of variation = 46 %) and 4.5 min (coefficient of variation = 22 %), respectively. ConclusionsDue to the high variability observed, the %Δ method does not effectively normalise the relative intensity of exhaustive high-intensity interval training across individuals. The generally larger inter- versus intra-individual variability suggests that day-to-day biological fluctuations and/or measurement errors cannot explain the identified shortcoming of the method.

Development and Validity of Norms for Cognitive Dispersion on the Uniform Data Set 3.0 Neuropsychological Battery.

Cognitive dispersion indexes intraindividual variability in performance across a battery of neuropsychological tests. Measures of dispersion show promise as markers of cognitive dyscontrol and everyday functioning difficulties; however, they have limited practical applicability due to a lack of normative data. This study aimed to develop and evaluate normed scores for cognitive dispersion among older adults. We analyzed data from 4,283 cognitively normal participants aged ≥50years from the Uniform Data Set (UDS) 3.0. We describe methods for calculating intraindividual standard deviation (ISD) and coefficient of variation (CoV), as well as associated unadjusted scaled scores and demographically adjusted z-scores. We also examined the ability of ISD and CoV scores to differentiate between cognitively normal individuals (n = 4,283) and those with cognitive impairment due to Lewy body disease (n = 282). We generated normative tables to map raw ISD and CoV scores onto a normal distribution of scaled scores. Cognitive dispersion indices were associated with age, education, and race/ethnicity but not sex. Regression equations were used to develop a freely accessible Excel calculator for deriving demographically adjusted normed scores for ISD and CoV. All measures of dispersion demonstrated excellent diagnostic utility when evaluated by the area under the curve produced from receiver operating characteristic curves. Results of this study provide evidence for the clinical utility of sample-based and demographically adjusted normative standards for cognitive dispersion on the UDS 3.0. These standards can be used to guide interpretation of intraindividual variability among older adults in clinical and research settings.

Neuropsychological Impairment, Brain Injury Symptoms, and Health-Related Quality of Life After Pediatric TBI in Oslo.

Descriptions of clinical outcomes in pediatric traumatic brain injury (pTBI) in Scandinavia are sparse. The Oslo site of the European CENTER-TBI study has performed a pTBI outcome study in a hospitalized population. The main objective was to investigate neuropsychological outcomes, self- and parent-reported symptoms associated with brain injury, and quality of life in children aged 1–15 years, 5–8 months after injury. Fifty-two children were included, and 45 completed the assessments. The sample consisted of 15.4% severe, 21.2% moderate, and 63.4% mild TBI. Subjectively experienced problems with concentration and fatigue were reported by the parents of nearly half of the children. Higher brain injury symptom load was associated with lower quality of life, but was unrelated to injury severity. Group average scores of the sample on neuropsychological testing appeared unimpaired relative to normative means aside from lower performance in working memory. However, based on an impairment index (i.e., 2 or more tests being >1.5 SD below the normative mean), the presence of weak cognitive performance was evident in as many as 45.4% of the sample. Two-thirds of the sample also showed abnormally large intraindividual variability in cognitive functioning (i.e., significant WISC-IV index discrepancies). The findings highlight the need to look beyond group averages on neuropsychological testing. Utilizing an impairment index and considering intraindividual performance variability conveyed deficits that may warrant clinical follow-up. The association of brain injury symptoms with quality of life but not injury severity emphasizes the need to consider symptoms after TBI within a biopsychosocial framework.Clinical Trial Registration: ClinicalTrials.gov; identifier: NCT02210221.

Cognitive aspects of attention disorders in Alzheimer's disease.

Attention deficits are encountered at a very early stage in the development of Alzheimer's disease. While these deficits may be detected using classic clinical tests or even through simple observation, experimental tools enable a more precise evaluation of these deficits, typically by differentiating between conditions in which the quantity of attention needed varies, and by recording response times, which allows for a more precise and modulated measurement. The sensitivity of these tools can be further increased by analysing the intra-individual variability of performance in these experiments, which is particularly significant during the earliest stages of the disease. We present the cognitive aspects of these deficits by regrouping them according to the type of experiment used to highlight each deficit. We therefore distinguish spatial attention orientation deficits, executive control deficits, and sustained attention deficits. In each section, we present some of the more commonly used experiments (spatial cueing, spatial search, dual tasks, conflict tasks, vigilance tests), and draw parallels between these experiments and everyday life.

Cognitive aspects of attention deficits in Alzheimer's disease

Attention deficits are encountered very early in the development of Alzheimer's disease. While these deficits may be detected using classic clinical tests or even from simple observation, experimental tools enable a more precise evaluation of these deficits, typically by subtracting between conditions which vary the quantity of necessary attention, and by recording response times which allow a more precise and modulated measurement. The sensitivity of these tools can be further increased by analyzing the intra-individual variability of performance in these experiments, this variability being particularly important during the earliest stages of the disease. We present the cognitive aspects of these deficits by regrouping them according to the type of experiment used to highlight each deficit. Thus, we distinguish deficits of spatial attention orientation, of executive control and of sustained attention. In each section we present several of the more often employed experiments (spatial cueing, spatial search, dual-tasks, conflict tasks, vigilance tests), and draw a parallel between these experiments and everyday life.

A novel approach to intra-individual performance variability in ADHD

Patients with attention deficit/(hyperactivity) disorder (AD(H)D) show increased intra-individual variability (IIV) in behavioral performance. This likely reflects dopaminergic deficiencies. However, the precise performance profile across time and the pattern of fluctuations within it have not yet been considered, partly due to insufficient methods. Yet, such an analysis may yield important theory-based implications for clinical practice. Thus, in a case–control cross-sectional study, we introduce a new method to investigate performance fluctuations in patients with ADD (n = 76) and ADHD (n = 67) compared to healthy controls (n = 45) in a time estimation task. In addition, we also evaluate the effects of methylphenidate (MPH) treatment on this performance pattern in 29 patients with AD(H)D. Trial-by-trial differences in performance between healthy controls and patients with AD(H)D do not persist continuously over longer time periods. Periods during which no differences in performance between healthy controls and patients occur alternate with periods in which such differences are present. AD(H)D subtype and surprisingly also medication status does not affect this pattern. The presented findings likely reflect (phasic) deficiencies of the dopaminergic system in patients with AD(H)D which are not sufficiently ameliorated by first-line pharmacological treatment. The presented findings carry important clinical and scientific implications.

GOLF SWING VARIABILITY IN ELITE FEMALE JUNIOR GOLFERS

The aim of the study was to determine the variability of golf swing execution in lower and upper body parameters for two golf clubs. Eleven elite female golfers of junior age volunteered in the study and performed 10 trials with mid-iron and with driver at laboratory conditions. A 3D motion capture system was used to measure the lower and upper body movement parameters and club head speed. To assess variability, the coefficient of variation (CV%) and biological coefficient of variation (BCV%) were calculated. Two-tailed t test was used to identify differences between mid-iron and driver variability for each selected kinematic parameter. Any significant difference in variability of kinematics parameters was found between mid-iron club and driver club. However, for both clubs, we found high stability of performance in timing parameters and of lower limbs kinematic parameters at three selected moments of the golf swing. We conclude that timing stability may be the key to achieve the effective and repeatable golf swing in both golf clubs types and that high intra-individual variability of performance may be due to large age range in the study group.

Are there Any Differences in Simple and Random Choice Motor Task Performance between Young and Middle-Aged Adults?

Research background and hypothesis. Most studies are based on elderly subjects’ results, so there is a need to explore if motor performance changes begin in the middle age. We hypothesize that (i) middle-aged subjects use “play it safe” strategy, which depends on the type of tasks (simple vs. random choice); (ii) middle-aged subjects will show higher intra-individual performance variability compared to young adults, furthermore, simple task will show lower performance variability.Research aim was to establish if there were any movement performance differences during simple and random choice motor task performance between young and middle-aged adults.Research methods. Middle-aged and young adults performed two speed-accuracy tasks. During simple task participants had to reach the same target which appeared in the same place and during random choice task the target appeared randomly in one of the three different places.Research results. Data showed that middle-aged group had slower (p < 0.05) reaction time and maximal velocity, whereas movement path length was more accurate (p < 0.05) than that in the young adult group. Comparing different tasks it was observed that during simple task reaction time was faster (p < 0.05) than in the random choice task in both groups. Intra-individual variability of reaction time and maximal velocity was higher (p < 0.05) in the middle-aged group, whereas no changes were observed between different tasks.Discussion and conclusion. Motor performance strategy “play it safe” is already observed for the middle- aged population: they decrease maximal velocity and reaction time in order to make movement more accurate. Additionally, they demonstrate task-independent higher intra-individual variability of reaction time and maximal velocity showing changes in CNS integrity compared to young adults.Keywords: aging, speed-accuracy tasks, intra-individual variability.

Intraindividual variability in performance on associative memory tasks is elevated in amnestic mild cognitive impairment

Elevations in intraindividual variability (IIV) are an indicator of neurocognitive compromise and are seen on reaction time tasks in individuals with mild cognitive impairment (MCI). We examined IIV on memory tasks known to be sensitive to early cognitive change in a group of 24 individuals with amnestic MCI and 21 matched controls. Traditional measures of accuracy and speed, as well as indices of IIV statistically purified for systematic between-group and trial effects, were derived from performance on two computer-based associative recognition tests of word–word and face-name pairs. Accuracy and speed were reduced and IIV was elevated in the MCI group compared to controls on both tasks. Logistic regression analyses demonstrated that IIV, but not speed, was a unique predictor of group membership, over and above performance accuracy. Observed elevations in IIV in MCI are congruent with the notion that IIV may reflect disturbance in distributed neural networks, including medial temporal regions, in addition to frontal systems dysfunction. Present findings have diagnostic implications for accurate identification of individuals with MCI and add to the growing literature on IIV as an early indicator of cognitive decline in older adults.

The neuropsychological assessment of cognitive deficits considering measures of performance variability.

Neuropsychologists often face interpretational difficulties when assessing cognitive deficits, particularly in cases of unclear cerebral etiology. How can we be sure whether a single test score below the population average is indicative of a pathological brain condition or normal? In the past few years, the topic of intra-individual performance variability has gained great interest. On the basis of a large normative sample, two measures of performance variability and their importance for neuropsychological interpretation will be presented in this paper: the number of low scores and the level of dispersion. We conclude that low scores are common in healthy individuals. On the other hand, the level of dispersion is relatively small. Here, base rate information about abnormally low scores and abnormally high dispersion across cognitive abilities are provided to improve the awareness of normal variability and to serve clinicians as additional interpretive measures in the diagnostic process.

A new approach to assessing intra-subject variability in single-subject designs

A new approach to assessing intra-subject variability in single-subject designs

Neuropsychological Profile and Performance Variability in Vascular Cognitive Impairment

Background: Cognitive impairment from cerebrovascular disease varies in scope. Methods: We studied healthy elderly individuals and those with mild cognitive impairment (MCI) or mild dementia attributed to vascular pathology, in order to assess the diagnostic utility of intra-individual variability across neuropsychological domains and the cognitive profile of vascular cognitive disorders. A large battery of tests was used to create z-scores for seven neuropsychological domains by principle components analysis. Results: We did not find group differences in the average intra-individual variance across neuropsychological domains. We did find group differences in the within-domain variability for Language, reflecting increased performance variability in those participants with vascular pathology. There was a lower inter-correlation of domain scores in the MCI group than in the mild vascular dementia (VD) group. The MCI group had the largest deficits in Executive Function, Fluency and Memory relative to the healthy control (HC) group. The VD group evidenced a broad range of further cognitive decline relative to the MCI group, with the largest difference on Visuoconstruction. Conclusions: While intra-individual performance variability may increase early in the course of cognitive decline from vascular pathology, this is not because of greater across-domain variability or because impairments occur in only one particular cognitive domain or small cluster of inter-related domains. Early cognitive change includes decreased executive function that cannot be attributed to slow information processing or response time.

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.

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.

Intraindividual variability in HIV infection: Evidence for greater neurocognitive dispersion in older HIV seropositive adults.

Both the prevalence and incidence of HIV infection among older adults are on the rise. Older adults are at increased risk of HIV-associated neurocognitive disorders, which have historically been characterized as an inconsistent or "spotty" pattern of deficits. Dispersion is a form of intraindividual variability (IIV) that is defined as within-person variability in performance across domains and has been associated with poorer neurocognitive functioning and incipient decline among healthy older adults. To our knowledge, no studies have yet examined dispersion in an aging HIV-infected sample. For the current study we examined the hypothesis that age and HIV infection have synergistic effects on dispersion across a battery of clinical and experimental cognitive tasks. Our well-characterized sample comprised 126 HIV-seropositive individuals (HIV+) and 40 HIV-seronegative comparison individuals (HIV-), all of whom were administered a comprehensive neuropsychological battery. Consistent with our hypothesis, an age by HIV serostatus interaction was observed, with the older HIV+ group demonstrating a higher level of dispersion relative to older HIV- and younger HIV+ individuals, even when potentially confounding demographic and medical factors were controlled. Our results demonstrate that older HIV+ adults produce greater dispersion, or intraindividual variability in performance across a range of tests, which may be reflective of cognitive dyscontrol to which this population is vulnerable, perhaps driven by the combined effects of aging and HIV infection on prefrontostriatal systems.

Aerobic fitness and response variability in preadolescent children performing a cognitive control task.

To investigate the relationship between aerobic fitness and cognitive variability in preadolescent children. Forty-eight preadolescent children (25 males, 23 females, mean age = 10.1 years) were grouped into higher- and lower-fit groups according to their performance on a test of aerobic capacity (VO2max). Cognitive function was measured via behavioral responses to a modified flanker task. The distribution in reaction time was calculated within each participant to assess intraindividual variability of performance. Specifically, the standard deviation and coefficient variation of reaction time were used to represent cognitive variability. Preadolescent children, regardless of fitness, exhibited longer reaction time, increased response variability, and decreased response accuracy to incongruent compared to congruent trials. Further, higher-fit children were less variable in their response time and more accurate in their responses across conditions of the flanker task, while no group differences were observed for response speed. These findings suggest that fitness is associated with better cognitive performance during a task that varies cognitive control demands, and extends this area of research to suggest that intraindividual variability may be a useful measure to examine the relationship between fitness and cognition during preadolescence.

A Fragile Balance: Perturbation of GABA Mediated Circuit in Prefrontal Cortex Generates High Intraindividual Performance Variability

High intraindividual performance variability is one of the most robust findings to emerge in cognitive-experimental research of attention deficit hyperactivity disorder (ADHD). Evidences from studies incorporating structural or functional human brain mapping methods indicate that this increased intraindividual variability is not simply a sequel of general brain dysfunction, but is likely related to the functioning of neural circuits that engage the prefrontal cortex, particularly the dorsolateral areas (dlPFC). In order to examine further the anatomical and pharmacological substrate responsible for this high intraindividual variability disorder, we injected GABAA antagonist (bicuculline) or GABAA agonist (muscimol) in the dlPFC of monkeys performing a reflexive oculomotor task. Here we show that, whereas GABAA agonist injection induced no or minimal impairments, injection of GABAA antagonist dramatically increased the intraindividual variability of saccade response time and of saccade spatial accuracy (amplitude and direction). Overall, this study demonstrates that the balance between excitatory/inhibitory activities in the dlPFC is fragile but crucial, since local micro-injection of GABAA antagonist can induce marked behavioural effects. It also reveals that higher cognitive areas such as the dlPFC are markedly capable to influence the productions and metrics of reflexive movements. Altogether, this study provides promising perspectives for the development of new therapeutic strategies for the treatment of diseases in which high intravariability disorders are a prominent feature.

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.

Word-List-Learning Performance in Younger and Older Adults: Intra-Individual Performance Variability and False Memory

ABSTRACT We investigated the word-list-learning performance of younger and older adults over 4 consecutive days at different times of day to study age-related differences in consistency of performance over time and the influence of circadian variation on performance. Eighteen younger (M age, 23.4 years) and 18 older (M age, 73.3 years) men and women participated. The start time of testing alternated between morning and early evening across the 4 days of testing. On each test day, participants learned a different list of 15 unrelated words over four learning trials. As expected, younger adults performed better than older adults on immediate recall, delayed recall, and recognition. Contrary to our expectations, time of day did not significantly influence recall or recognition performance in either the older or younger adults. Older adults did show a greater incidence of false memory (i.e., previously learned list intrusions in free recall and false alarms in recognition) than younger adults. Older adults also exhibited greater intra-individual performance variability on the measures of false memory across test days. This variability was not related to circadian variation. False memory and variability of performance have both been linked to frontal systems dysfunction. The findings presented here are consistent with the notion that changes in cognition with aging in part reflect age-related decline in frontal lobe function.

Cingulate Activation Increases Dynamically with Response Speed under Stimulus Unpredictability

Functional magnetic resonance imaging studies of cognition require repeated and consistent engagement of the cognitive process under investigation. Activation is generally averaged across trials that are assumed to tax a specific mental operation or state, whereas intraindividual variability in performance between trials is usually considered error variance. A more recent analysis approach postulates that these fluctuations can reflect variation in the very process taxed by the particular trial type. In the present study, participants responded to targets presented randomly in 1 of 4 peripheral locations. By employing a function of reaction time (RT) of individual trials as a linear regressor, brain regions were identified whose activation varied with RT on a trial-by-trial basis. Whole-brain analysis revealed that the anterior cingulate, posterior cingulate, and left angular/superior temporal gyri were more active in trials with faster RT but only when the target location was unpredictable. No such association was seen in trials where the target location was predicted by a central cue. These results suggest a role for the cingulate and angular gyri in the dynamic regulation of attention to unpredictable events. This is in accordance with the function of a default network that is active in the absence of top-down-focused attention and is thought to continuously provide resources for broad and spontaneous information gathering. Exploiting intertrial performance variability may be particularly suitable for capturing such spontaneous and elusive phenomena as stimulus-driven processes of attention.