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Interaction-dominant dynamics in human cognition: Beyond 1/ƒα fluctuation

It has been suggested that human behavior in general and cognitive performance in particular emerge from coordination between multiple temporal scales. In this article, we provide quantitative support for such a theory of interaction-dominant dynamics in human cognition by using wavelet-based multifractal analysis and accompanying multiplicative cascading process on the response series of 4 different cognitive tasks: simple response, word naming, choice decision, and interval estimation. Results indicated that the major portion of these response series had multiplicative interactions between temporal scales, visible as intermittent periods of large and irregular fluctuations (i.e., a multifractal structure). Comparing 2 component-dominant models of 1/f(alpha) fluctuations in cognitive performance with the multiplicative cascading process indicated that the multifractal structure could not be replicated by these component-dominant models. Furthermore, a similar multifractal structure was shown to be present in a model of self-organized criticality in the human nervous system, similar to a spatial extension of the multiplicative cascading process. These results illustrate that a wavelet-based multifractal analysis and the multiplicative cascading process form an appropriate framework to characterize interaction-dominant dynamics in human cognition. This new framework goes beyond the identification of 1/f(alpha) power laws and non-gaussian distributions in response series as used in previous studies. The present article provides quantitative support for a paradigm shift toward interaction-dominant dynamics in human cognition.

Physical activity monitoring by use of accelerometer-based body-worn sensors in older adults: A systematic literature review of current knowledge and applications

OBJECTIVES To systematically review the literature on physical activity variables derived from body-worn sensors during long term monitoring in healthy and in-care older adults. METHODS Using pre-designed inclusion and exclusion criteria, a PubMed search strategy was designed to trace relevant reports of studies. Last search date was March 8, 2011. STUDY SELECTION Studies that included persons with mean or median age of >65 years, used accelerometer-based body-worn sensors with a monitoring length of >24h, and reported values on physical activity in the samples assessed. RESULTS 1403 abstracts were revealed and 134 full-text papers included in the final review. A variety of variables derived from activity counts or recognition of performed activities were reported in healthy older adults as well as in in-care older adults. Three variables were possible to compare across studies, level of Energy Expenditure in kcal per day and activity recognition in terms of total time in walking and total activity. However, physical activity measured by these variables demonstrated large variation between studies and did not distinguish activity between healthy and in-care samples. CONCLUSION There is a rich variety in methods used for data collection and analysis as well as in reported variables. Different aspects of physical activity can be described, but the variety makes it challenging to compare across studies. There is an urgent need for developing consensus on activity monitoring protocols and which variables to report.

Training infant treadmill stepping: The role of individual pattern stability

In this study, we investigated the responsiveness of a developing neuromotor system to training: When is training effective and when are the effects specific to the training condition? Eight infants, six 3-month-olds and two 7-month-olds, received month-long daily training on either a fast-running treadmill, a slow-running treadmill, or a stationary treadmill. Two additional 3-month-old infants served as controls and received no training. Results showed that training led to an increased number of steps. This improvement was inversely related to initial performance: Training had more effect on infants that initially performed unstable stepping patterns. Furthermore, training facilitated the transition from multiple stepping patterns to more alternate stepping. Again, initial pattern preferences influenced these effects of training and often remained visible throughout training. Infants responses to training at specific speeds were less clear-cut, but some indications were found that this also depended on their initial performances as well as on the characteristics of training. In general, when initial performances corresponded to the training condition, they were strengthened. When they were different from the training condition, training effects generalized to other speeds. These results suggest that the developing neuromotor system is amenable to training whenever performance is unstable, and that training effects interact with the individuals initially preferred patterns. These results are consistent with a dynamic systems view of motor development.

Posture and the emergence of manual skills

In this paper, we examine how infants’ natural manual and postural activities — what they prefer and do week by week — are related to developmental transitions in reaching skill and its neuromuscular control. Using a dense, longitudinal design, we tracked the manual and postural activities of four infants in a natural, free-play setting across the first year of life, and related these activities to two transitions in reaching as measured in a structured laboratory setting: the transition to reaching and the transition to stable reaching. Our data indicated that specific advances in the free-play setting preceded both transitions. Head and upper torso control, the ability to extend the arm and hand to a distant target, and the ability to touch and grasp objects placed nearby were all precursors to the onset of reaching, whereas sitting independently was associated with the transition to stable reaching. We also found important individual variability in when these ‘components’ were in place, indicating that it is the ensemble of components that is essential, not the order in which they develop or the timing of their contribution. These findings suggest that subsequent experimental manipulations should be planned with respect to infants’ individual constellations of skills, rather than looking at only a single precursor to change.

The Complexity of Childhood Development: Variability in Perspective

The complexity of childhood development is exemplified in the variability of development that is seen across tasks and individuals. Furthermore, variability in performance is omnipresent within individuals across repetitions of a task and across individuals performing the same task. Previously, this variability was thought to reflect error of measurement or error of execution. On this account, variability reflects noise that should be filtered or averaged out of the data in order to reveal the “true” underlying characteristics of the performance. Although errors of measurement and execution indeed contribute to variability in movements, research in the last 2 decades has revealed characteristics of variability that are far more interesting than just noise. These characteristics can be deeply informative about underlying control processes and point to directions for clinical practice. This perspective article reviews different ways of characterizing variability, illustrates changes in variability as a result of development and learning, and discusses different theoretical perspectives on the role of variability that give clues about how to understand changes in variability and how to deal with variability in clinical settings.

Measuring physical fitness in children who are 5 to 12 years old with a test battery that is functional and easy to administer.

Background Valid and reliable measures of childrens physical fitness are necessary for investigating the relationship between childrens physical fitness and childrens health. Objective The objective of this study was to estimate the feasibility, internal consistency, convergent construct validity, and test-retest reliability of a new, functional, and easily administered test battery for measuring childrens physical fitness. Design The study was a cross-sectional descriptive survey applying physical fitness tests across age groups 5 to 12 years. Methods Each of the 9 items in the test battery consists of a compound motor activity that recruits various combinations of endurance, strength (force-generating capacity), agility, balance, and motor coordination: standing broad jump, jumping a distance of 7 m on 2 feet, jumping a distance of 7 m on one foot, throwing a tennis ball with one hand, pushing a medicine ball with 2 hands, climbing wall bars, performing a 10 × 5 m shuttle run, running 20 m as fast as possible, and performing a reduced Cooper test (6 minutes). The test battery was administered to 195 children (aged 5–12 years) from 4 schools and kindergartens in Norway. Results Overall, the children in each age group were able to perform all of the test items, indicating the suitability of the test battery for children as young as 5 years of age. With increasing age, total scores improved linearly, indicating the adequate sensitivity of the test battery for the age range examined in this study. Furthermore, even with the modest sample size used in this study, total scores were normally distributed, thereby fulfilling the necessary assumptions of most statistical procedures. For investigating the reliability of the test battery, 24 children (mean age=8.6 years) in one class were retested 1 week later. Test-retest correlations were high, with intraclass correlation coefficients for individual test items and total score ranging from .54 to .92. Limitations The survey was limited to samples of 5- to 12-year-old Norwegian children. Larger samples in each age group are essential for establishing age- and sex-specific norms. Conclusions These promising results warrant further development of the test battery, including standardization and normalization based on a large, representative sample.

Relationship between neuromuscular body functions and upper extremity activity in children with cerebral palsy.

Aim  Our aim was to investigate the relationship between the dimensions of neuromuscular body function and elbow, forearm, and hand activity in the upper extremities in children/adolescents with spastic cerebral palsy (CP), within the framework of the World Health Organization International Classification of Functioning, Disability and Health.

Altered vision destabilizes gait in older persons

This study assessed the effects of dim light and four experimentally induced changes in vision on gait speed and footfall and trunk parameters in older persons walking on level ground. Using a quasi-experimental design, gait characteristics were assessed in full light, dim light, and in dim light combined with manipulations resulting in reduced depth vision, double vision, blurred vision, and tunnel vision, respectively. A convenience sample of 24 home-dwelling older women and men (mean age 78.5 years, SD 3.4) with normal vision for their age and able to walk at least 10 m without assistance participated. Outcome measures were gait speed and spatial and temporal parameters of footfall and trunk acceleration, derived from an electronic gait mat and accelerometers. Dim light alone had no effect. Vision manipulations combined with dim light had effect on most footfall parameters but few trunk parameters. The largest effects were found regarding double and tunnel vision. Men increased and women decreased gait speed following manipulations (p=0.017), with gender differences also in stride velocity variability (p=0.017) and inter-stride medio-lateral trunk acceleration variability (p=0.014). Gender effects were related to differences in body height and physical functioning. Results indicate that visual problems lead to a more cautious and unstable gait pattern even under relatively simple conditions. This points to the importance of assessing vision in older persons and correcting visual impairments where possible.

The influence of center-of-mass movements on the variation in the structure of human postural sway

The present article investigates the influence of center-of-mass movements on the variation of the structure in human postural sway. Twelve healthy younger persons performed 60s quiet standing, 60s relaxed standing, and 10 min relaxed standing on two force plates. Center-of-pressure (CoP) and gravitational line (GL) profiles were calculated from the ground reaction forces and moments. The temporal variation of CoP structure was calculated by the local scaling exponent h(t) and a Monte Carlo surrogate test was used to identify phase couplings between temporal scales. The range of variation of h(t) was significantly larger in relaxed standing compared to quiet standing (p<0.00001) and highly correlated with the range of GL movements (r>0.76, p<0.001). However, the variation in h(t) was not generated by the GL movements because the CoP-GL traces was close to identical variation in h(t) (r>0.95, p<0.00001). The Monte Carlo surrogate test indicated the presence of intermittent phase couplings between the temporal scales of both CoP traces and the CoP-GL residuals in the periods with GL movements. The present results suggest that human posture is controlled by intermittent phase coupling of the CoP and GL movements. Furthermore, the investigation of the variation in CoP structure might extend existing theories of changes in postural control for example older persons and patients with a neurodegenerative disease.

Multifractal formalisms of human behavior

With the mounting realization that variability is an inevitable part of human behavior comes the need to integrate this phenomenon in concomitant models and theories of motor control. Among other things, this has resulted in a debate throughout the last decades about the origin of variability in behavior, the outcome of which has important implications for motor control theories. To date, a monofractal formalism of variability has been used as the basis for arguing for component- versus interaction-oriented theories of motor control. However, monofractal formalism alone cannot decide between the opposing sides of the debate. The present theoretical overview introduces multifractal formalisms as a necessary extension of the conventional monofractal formalism. In multifractal formalisms, the scale invariance of behavior is numerically defined as a spectrum of scaling exponents, rather than a single average exponent as in the monofractal formalism. Several methods to estimate the multifractal spectrum of scaling exponents - all within two multifractal formalisms called large deviation and Legendre formalism - are introduced and briefly discussed. Furthermore, the multifractal analyses within these two formalisms are applied to several performance tasks to illustrate how explanations of motor control vary with the methods used. The main section of the theoretical overview discusses the implications of multifractal extensions of the component- and interaction-oriented models for existing theories of motor control.