Scoping review of dual-task interference in individuals with intellectual disability.

Dual-task paradigms can provide insights on the structures and mechanisms underlying information processing and hold diagnostic, prognostic, and rehabilitative value for populations with cognitive deficits such as in individuals with intellectual disability (ID). In this paradigm, two tasks are performed separately (single-task context) and concurrently (dual-task context). The change in performance from single- to dual-task context represents dual-task interference. Findings from dual-task studies have been largely inconsistent on whether individuals with ID present with dual-task-specific deficits. The current review aimed to map the published literature on dual-task methods and pattern of dual-task interference in individuals with ID. A scoping review based on Arksey and O'Malley's five-stage methodological framework was performed. Seventeen electronic databases and registries were searched to identify relevant studies, including gray literature. Charted data from included studies were analyzed quantitatively and qualitatively. PRISMA guidelines informed the reporting of this review. Twenty-two studies involving 1,102 participants (656 with ID and 446 without ID) met the review's inclusion criteria. Participants in the included studies were heterogeneous in sex, age (range 3-59 years), etiology and ID severity. Included studies characterized their ID-sample in different ways, most commonly using intelligence quotient (IQ) scores. Other measures of intellectual function (e.g., mental age, ID severity, verbal and/or visuospatial ability scores) were also used, either solely or in combination with IQ. Methods of dual-task testing varied across studies, particularly in relation to dual-task combinations, equation of single-task performance between groups, measurement and reporting of dual-task performance for each single-task, and task priority instructions. Thematic content of the included studies were: (1) structural interference to dual-tasking; (2) etiology-based differences in dual-tasking; (3) gait and balance dual-task performance; (4) testing executive function using dual-task paradigms; and (5) training effect on dual-task performance. Although the evidence consistently supported the intact dual-tasking ability of individuals with ID, the pattern of dual-task interference was inconsistent. Likewise, the evidence was inconclusive regarding dual-task deficit specific to individuals with ID because of heterogeneity in dual-task study designs among included studies.

Athletes with intellectual disability: The effects of cognitive deficits and sports practice on bipedal standing balance.

BACKGROUND: Athletes with intellectual disability represent a unique population who experiences the contrasting effects of cognitive deficits and benefits of sports on balance. This study investigated the combined impact of intellectual disability and sport practice on balance. METHOD: Center-of-pressure excursion in bipedal stance of 2 disability (with and without intellectual disability) × 2 sport practice (athlete and novice) participant groups was measured in several balance conditions. RESULTS: Sport practice exerted no significant effect on any of the center-of-pressure measures used. In contrast, intellectual disability's effects on balance, which were most apparent in challenging balance conditions, were significant (p < .05) and had large effect sizes (ηp 2 > 0.13). CONCLUSION: The negative effects of cognitive deficits on the balance of young adults with intellectual disability underscore the need for effective interventions. Although findings did not support sports' balance-remediating potential, the value of sport participation for individuals with intellectual disability cannot be fully dismissed just yet.

Cognitive-motor multitasking in athletes with and without intellectual impairment.

PURPOSE: We investigated cognitive-motor multitasking in 29 top athletes with intellectual impairment (II) recruited during the European Championship Games organized by Virtus (World Intellectual Impairment Sports) and 29 control (CT) athletes matched for age, sex, sports practiced, and lifetime accumulated practice hours. METHODS: Participants performed a cognitive task that required recognizing previously displayed visual objects among distractors. The motor task required maintaining a stable upright posture balancing on a rocking board placed atop a force plate which assessed center-of-pressure (COP) movement. Both tasks were performed separately (with participants seated for the cognitive single task) and concurrently under dual-task conditions, wherein participants memorized objects while balancing. We analyzed recognition accuracy, COP path length, and sample entropy of the COP trajectory as a measure for automaticity of postural control. RESULTS: As expected, CT-athletes outperformed II-athletes in the cognitive task but the two groups have comparable performance in the postural task under single- and dual-task conditions. When multitasking, CT-athletes switched to more automatic postural control and maintained their postural sway at single-task levels. II-athletes prioritized balance thereby successfully keeping COP excursion comparable to single-task conditions. However, this came with pronounced costs for memory performance, which was unaffected by multitasking in CT-athletes. CONCLUSION: The adaptive capacity observed in control athletes was not at the disposal of II-athletes who revealed pronounced sensitivities to multitasking interference. This sensitivity obviously was not compensated for by either athletic competence or potential transfer of athletic skill to domain-general cognitive functions.

Reliability of center of pressure excursion as a measure of postural control in bipedal stance of individuals with intellectual disability: A pilot study.

The high prevalence of postural instability in individuals with intellectual disability (ID) warrants the need for reliable and practical postural control assessments. Stabilometry is a postural control assessment that has been widely used for clinical populations. However, the scant systematic knowledge about the reliability of stabilometric protocols for adults with ID renders results questionable and limits its value for clinicians and researchers. The study's purpose was to develop a stabilometric protocol for adults with and without ID based on optimal combinations of shortest necessary trial durations and the least number of trial repetitions that guarantee sufficient reliability. Participants performed six trials of bipedal standing in 2 vision (eyes open vs eyes closed) x 2 surface (solid vs compliant) conditions on a force platform. Several parameters were calculated from the first 10-, 20-, and 30-s interval of every center-of-pressure (COP) trial data. For different trial durations, we identified the number of trials that yielded acceptable relative (intraclass correlation coefficient ≥ 0.70) and absolute (standard error of measurement < 20%) reliability using the Spearman-Brown prophecy formula. To determine the optimal combination of trial duration and number of repetition for each COP parameter, we implemented a two-step process: 1) identify the largest number of repetition for each of the three trial durations and then 2) select the trial duration with the lowest number of repetition. For both ID- and non-ID groups, we observed a trend whereby shorter trial durations required more repetitions and vice versa. The phase plane and ellipse area were the most and least reliable center-of-pressure parameter, respectively. To achieve acceptable reliability, four 30-s trials of each experimental condition appeared to be optimal for testing participants with and without ID alike. The results of this research can inform stabilometric test protocols of future postural control studies of adults with ID.

Haptic two-dimensional shape identification in children, adolescents, and young adults.

We investigated the influence of image mediation (the process that translates tactile information into a visual image) on the development of haptic two-dimensional (2D) shape identification in 78 participants from five different age groups: preschoolers (4-5 years), first graders (6-7 years), fifth graders (10-11 years), young adolescents (12-13 years), and young adults (18-28 years). Participants attempted to haptically recognize everyday objects (three-dimensional [3D] haptic condition) and tangible line drawings (2D haptic condition) and to recognize objects presented through a serial visual "peek hole" version of the haptic line drawing task (2D visual condition). All groups were excellent at 3D haptic identification. However, preschoolers and first graders scored low in both visual and haptic line drawing tasks. From fifth grade onward, participants were reliably better at the visual peek hole task compared with the haptic line drawing task, which improved only gradually in young adolescent and adult age groups. We argue that both the spatial reference frame and working memory capacity constrain image mediation and children's increasing abilities to correctly haptically identify 2D shapes.

Ecological Relevance Determines Task Priority in Older Adults' Multitasking.

OBJECTIVES: Multitasking is a challenging aspect of human behavior, especially if the concurrently performed tasks are different in nature. Several studies demonstrated pronounced performance decrements (dual-task costs) in older adults for combinations of cognitive and motor tasks. However, patterns of costs among component tasks differed across studies and reasons for participants' resource allocation strategies remained elusive. METHOD: We investigated young and older adults' multitasking of a working memory task and two sensorimotor tasks, one with low (finger force control) and one with high ecological relevance (postural control). The tasks were performed in single-, dual-, and triple-task contexts. RESULTS: Working memory accuracy was reduced in dual-task contexts with either sensorimotor task and deteriorated further under triple-task conditions. Postural and force performance deteriorated with age and task difficulty in dual-task contexts. However, in the triple-task context with its maximum resource demands, older adults prioritized postural control over both force control and memory. DISCUSSION: Our results identify ecological relevance as the key factor in older adults' multitasking.

Grouping by proximity in haptic contour detection.

We investigated the applicability of the Gestalt principle of perceptual grouping by proximity in the haptic modality. To do so, we investigated the influence of element proximity on haptic contour detection. In the course of four sessions ten participants performed a haptic contour detection task in which they freely explored a haptic random dot display that contained a contour in 50% of the trials. A contour was defined by a higher density of elements (raised dots), relative to the background surface. Proximity of the contour elements as well as the average proximity of background elements was systematically varied. We hypothesized that if proximity of contour elements influences haptic contour detection, detection will be more likely when contour elements are in closer proximity. This should be irrespective of the ratio with the proximity of the background elements. Results showed indeed that the closer the contour elements were, the higher the detection rates. Moreover, this was the case independent of the contour/background ratio. We conclude that the Gestalt law of proximity applies to haptic contour detection.

Perceptual grouping in haptic search: the influence of proximity, similarity, and good continuation.

We conducted a haptic search experiment to investigate the influence of the Gestalt principles of proximity, similarity, and good continuation. We expected faster search when the distractors could be grouped. We chose edges at different orientations as stimuli because they are processed similarly in the haptic and visual modality. We therefore expected the principles of similarity and good continuation to be operational in haptics as they are in vision. In contrast, because of differences in spatial processing between vision and haptics, we expected differences for the principle of proximity. In haptics, the Gestalt principle of proximity could operate at two distinct levels-somatotopic proximity or spatial proximity-and we assessed both possibilities in our experiments. The results show that the principles of similarity and good continuation indeed operate in this haptic search task. Neither of our proximity manipulations yielded effects, which may suggest that grouping by proximity must take place before an invariant representation of the object has formed. (PsycINFO Database Record (c) 2012 APA, all rights reserved).

Lifespan changes in multi-tasking: concurrent walking and memory search in children, young, and older adults.

We investigated dual-task performance of cognitive (semantic fluency) and sensorimotor tasks (walking) in 120 children and adults from four age groups (9-year olds, M=9.52 years; 11-year olds, M=11.51 years; young adults, M=25.34 years; older adults, M=64.28 years; N=30 per group). Distances walked during 90 s and numbers of category exemplars generated in the semantic fluency task showed an inverted U-shape function with age. In line with general resource models proportional dual-task costs in walking also showed a U-shaped relation as a function of age with pronounced decrements in the youngest and oldest groups. Only 9-year olds showed significant costs in the cognitive task. Individual differences in single-task performance accounted for more than half of the variance in dual-task performance. Reliable age-related residual variance implicated additional factors particularly in children's developing multi-tasking performances.

The costs of taking it slowly: fast and slow movement timing in older age.

We investigated adult age-differences in timing control of fast vs. slow repetitive movements using a dual-task approach. Twenty-two young (M = 24.23 yr) and 22 older adults (M = 66.64 yr) performed three cognitive tasks differing in working memory load and response production demands and they tapped series of 550-ms or 2100-ms target intervals. Single-task timing was comparable in both groups. Dual-task timing was characterized by shortening of produced intervals and increases in drift and variability. Dual-task costs for both cognitive and timing performances were pronounced at slower tapping tempos, an effect exacerbated in older adults. Our findings implicate attention and working memory processes as critical components of slow movement timing and sources of specific challenges thereof for older adults.

Adaptation and reintegration of proprioceptive information in young and older adults' postural control.

We investigated age-related changes in adaptation and sensory reintegration in postural control without vision. In two sessions, participants adapted their posture to sway reference and to reverse sway reference conditions, the former reducing (near eliminating) and the latter enhancing (near doubling) proprioceptive information for posture by means of support-surface rotations in proportion to body sway. Participants stood on a stable platform for 3 min (baseline) followed by 18 min of sway reference or reverse sway reference (adaptation) and finally again on a stable platform for 3 min (reintegration). Results showed that when inaccurate proprioception was introduced, anterior-posterior (AP) sway path length increased in comparable levels in the two age groups. During adaptation, young and older adults reduced postural sway at the same rate. On restoration of the stable platform in the reintegration phase, a sizeable aftereffect of increased AP path length was observed in both groups, which was greater in magnitude and duration for older adults. In line with linear feedback models of postural control, spectral analyses showed that this aftereffect differed between the two platform conditions. In the sway-referenced condition, a switch from low- to high-frequency COP sway marked the transition from reduced to normal proprioceptive information. The opposite switch was observed in the reverse sway referenced condition. Our findings illustrate age-related slowing in participants' postural control adjustments to sudden changes in environmental conditions. Over and above differences in postural control, our results implicate sensory reweighting as a specific mechanism highly sensitive to age-related decline.

Posture and cognition interfere in later adulthood even without concurrent response production.

We investigated adult age differences in dual-task costs in cognitive-sensorimotor settings without concurrent response production and with individually adjusted resource demands for the cognitive task. Twenty-four young adults (M=25.42 years, SD=3.55) and 23 older adults (M=68 years, SD=4.46) performed a cognitive task and two postural control tasks (standing on a stable and moving platform) both separately (single-task context) and concurrently (dual-task context). The cognitive task did not require response production during posture data collection and its difficulty was individually adjusted to 80% correct performance under single-task conditions. Results showed pronounced age differences in postural control in the moving platform condition, which increased further under dual-task conditions. Our findings support the assumption of increased cognitive resource demands for postural control in older adults. They extend existing work by taking two shortcomings of previous studies into account. We discuss cognitive and posture task constraints in this and previous studies as factors determining multi-tasking and its changes in later adulthood.

Working memory and postural control: adult age differences in potential for improvement, task priority, and dual tasking.

We investigate dynamic posture control and working memory (NBack) retest practice in young and older adults, focusing on older adults' potential for improvement in the component tasks but more importantly in dual-task performance. Participants performed the 2 tasks in 11 sessions under single- and dual-task conditions. Posture improvement was observed with retest practice for both groups. Increase in cognitive load after initial practice led to greater dual-task costs in both tasks in older adults and higher costs in memory in young adults. With continued practice, costs were reduced by both groups; however, the 2 groups focused improvement on different tasks: Older adults focused on posture but young adults on cognition. These results emphasize older adults' potential for improvement in dual-task performance and their flexibility to utilize the practice gains in posture to optimize cognitive performance.

Age differences between children and young adults in the dynamics of dual-task prioritization: body (balance) versus mind (memory).

Task prioritization can lead to trade-off patterns in dual-task situations. The authors compared dual-task performances in 9- and 11-year-old children and young adults performing a cognitive task and a motor task concurrently. The motor task required balancing on an ankle-disc board. Two cognitive tasks measured working memory and episodic memory at difficulty levels individually adjusted during the course of extensive training. Adults showed performance decrements in both task domains under dual-task conditions. In contrast, children showed decrements only in the cognitive tasks but actually swayed less under dual-task than under single-task conditions and continued to reduce their body sway even when instructed to focus on the cognitive task. The authors argue that children perform closer to their stability boundaries in the balance task and therefore prioritize protection of their balance under dual-task conditions.

Task prioritization in aging: effects of sensory information on concurrent posture and memory performance.

In older adults, cognitive resources play a key role in maintaining postural stability. In the present study, we evaluated whether increasing postural instability using sway referencing induces changes in resource allocation in dual-task performance leading older adults to prioritize the more age-salient posture task over a cognitive task. Young and older adults participated in the study which comprised two sessions. In the first session, three posture tasks (stable, sway reference visual, sway reference somatosensory) and a working memory task (n-back) were examined. In the second session, single- and dual-task performance of posture and memory were assessed. Postural stability improved with session. Participants were more unstable in the sway reference conditions, and pronounced age differences were observed in the somatosensory sway reference condition. In dual-task performance on the stable surface, older adults showed an almost 40% increase in instability compared to single-task. However, in the sway reference somatosensory condition, stability was the same in single- and dual-task performance, whereas pronounced (15%) costs emerged for cognition. These results show that during dual-tasking while standing on a stable surface, older adults have the flexibility to allow an increase in instability to accommodate cognitive task performance. However, when instability increases by means of compromising somatosensory information, levels of postural control are kept similar in single- and dual-task, by utilizing resources otherwise allocated to the cognitive task. This evidence emphasizes the flexible nature of resource allocation, developed over the life-span to compensate for age-related decline in sensorimotor and cognitive processing.

Adaptive task prioritization in aging: selective resource allocation to postural control is preserved in Alzheimer disease.

OBJECTIVE: With age, the performance of multiple tasks decreases, a pattern exaggerated in Alzheimer disease (AD). At the same time, recent research, based on adaptive theories of healthy aging, indicates a preference of older adults to allocate resources toward tasks of higher immediate value (e.g., postural control). This study investigated whether such models also hold for pathologic cognitive aging. METHOD: Using a dual-task paradigm, the authors combined a working memory with a postural control task under easy and difficult conditions in patients with AD, older adults, older adults low on performance on a cognitive marker test, and young adults (N = 40). Participants repeatedly performed a cognitive and a postural control task both simultaneously and in isolation over the course of eight sessions. RESULTS: Consistent with earlier studies on divided attention in age and AD, the authors found large dual-task performance decrements with age and more so in AD. When not challenged, patients with AD showed large performance decrements under dual-task conditions in both postural control and working memory. With increasing difficulty in the postural control task, however, older adults, and more so patients with AD, maintained a high level of functioning in postural control, as compared with working memory. CONCLUSION: The findings indicate that the theory of selective optimization with compensation extends to pathologic aging and have broad implications for models of dual-task performance and executive control in aging and AD.

Timing, sequencing, and executive control in repetitive movement production.

The authors demonstrate that the timing and sequencing of target durations require low-level timing and executive control. Sixteen young (M-sub(age) = 19 years) and 16 older (M-sub(age) = 70 years) adults participated in 2 experiments. In Experiment 1, individual mean-variance functions for low-level timing (isochronous tapping) and the sequencing of multiple targets (rhythm production) revealed (a) a dissociation of low-level timing and sequencing in both age groups, (b) negligible age differences for low-level timing, and (c) large age differences for sequencing. Experiment 2 supported the distinction between low-level timing and executive functions: Selection against a dominant rhythm and switching between rhythms impaired performances in both age groups and induced pronounced perseveration of the dominant pattern in older adults.

Aging, expertise and fine motor movement.

Age-graded decrements in accuracies and maximum speed of fine motor movements observed in numerous experimental studies have nurtured general factor explanations like the assumption of general age-related slowing of central cognitive processes. This review focuses on two domains of investigation that yielded challenges to general factor models. First, experimental approaches aiming at the decomposition of fine motor skills provide evidence for the dissociability of timing, sequencing, and executive control components that show differential rather than general age-related changes. Second, studies on cognitive-motor expertise demonstrate that age-related changes in critical skill components depend on individuals' time investments into specific practice activities. It is argued that the process dissociations observed at the behavioral level in developmental (i.e. age and expertise) studies reflect individuals' long-term adaptations to internal and external performance constraints. The outcomes of these adaptation processes are stable interindividual differences in component processes.

Synchronizing movements with the metronome: nonlinear error correction and unstable periodic orbits.

The control of human hand movements is investigated in a simple synchronization task. We propose and analyze a stochastic model based on nonlinear error correction; a mechanism which implies the existence of unstable periodic orbits. This prediction is tested in an experiment with human subjects. We find that our experimental data are in good agreement with numerical simulations of our theoretical model. These results suggest that feedback control of the human motor systems shows nonlinear behavior.