Karl M. Newell

Free(z)ing Degrees of Freedom in Skill Acquisition

Abstract This study reports an empirical investigation into Bernsteins (1967) ideas that in the early stages of the acquisition of a movement skill the coordination problem is reduced by an initial freezing out of degrees of freedom, followed later in the learning process by the release of these degrees of freedom and their incorporation into a dynamic, controllable system. “Freezing” degrees of freedom was made operational both as a rigid fixation of individual degrees of freedom and as the formation of rigid couplings between multiple degrees of freedom. Five subjects practiced slalom-like ski movements on a ski apparatus for 7 consecutive days. Results showed that at the early phases of learning, the joint angles of the lower limbs and torso displayed little movement, as expressed by their standard deviations and ranges of angular motion, whereas joint couplings were high, as shown by the relatively high cross correlations between joint angles. Over practice, angular movement significantly increased i...

Changing complexity in human behavior and physiology through aging and disease

Lipsitz and Goldberger proposed that there is a loss in the complexity of physiological and behavioral systems with aging and disease. Here, we show that this unidirectional view of the change in system complexity is too narrow in its consideration of the actual changes that occur with aging and disease. An increase or decrease in the complexity of a behavioral or physiological system output can occur and the direction of change is dependent on the confluence of constraints that channel the system dynamics. It is postulated that the observed increase or decrease in complexity with aging and disease is dependent on the nature of both the intrinsic dynamics of the system and the short-term change required to realize a local task demand.

Noise information transmission, and force variability

This study was designed to test the hypothesis derived from information theory that increases in the variability of motor responses result from increases in perceptual-motor noise. Young adults maintained isometric force for extended periods at different levels of their maximum voluntary contraction. Force variability (SD) increased exponentially as a function of force level. However, the signal-to-noise ratio (M/SD), an index of information transmission, as well as measures of noise in both the time (approximate entropy) and frequency (power spectrum) domains, changed according to an inverted U-shaped function over the range of force levels. These findings indicate that force variability is not directly related to noise but that force output noisiness is positively correlated with the amount of information transmitted.

Time scales in motor learning and development.

A theoretical framework based on the concepts and tools of nonlinear dynamical systems is advanced to account for both the persistent and transitory changes traditionally shown for the learning and development of motor skills. The multiple time scales of change in task outcome over time are interpreted as originating from the systems trajectory on an evolving attractor landscape. Different bifurcations between attractor organizations and transient phenomena can lead to exponential, power law, or S-shaped learning curves. This unified dynamical account of the functions and time scales in motor learning and development offers several new hypotheses for future research on the nature of change in learning theory.

Coordination, Control and Skill

In this chapter, I develop the interpretation of coordination, control and skill sketched by Kugler, Kelso and Turvey (1980, 1982). The orientation promoted here is primarily descriptive with the focus being the development of a framework for a useful operational distinction between the three terms. 1 believe one can draw on the interpretation of coordination, control and skill outlined by Kugler and colleagues without necessarily invoking the theoretical position advanced by this group, although it will become clear as this chapter unfolds, that I am sympathetic to this theoretical position.

Dimensional change in motor learning

Bernstein (The Co-ordination and Regulation of Movements, Pergamon, London, 1967) outlined a theoretical framework for the degrees of freedom problem in motor control that included a 3-stage approach to the reorganization of the peripheral biomechanical degrees of freedom in motor learning and development. We propose that Bernsteins conception of change through the stages of learning is too narrow in its consideration of the degrees of freedom problem and the actual pathways of change evident in motor learning. It is shown that change in both the organization of the mechanical degrees of freedom and the dimension of the attractor dynamic organizing motor output can either increase or decrease, according to the confluence of constraints imposed on action. The central issue determining directional change in dimension is whether the dimensionality of the task relevant intrinsic dynamic needs to be increased or decreased to realize new task demands.

Stochastic processes in postural center-of-pressure profiles

The stochastic processes of postural center-of-pressure profiles were examined in 3- and 5-year-old children, young adult students (mean 20 years), and an elderly age group (mean 67 years). Subjects stood still in an upright bipedal stance on a force platform under vision and nonvision conditions. The time evolutionary properties of the center-of-pressure dynamic were examined using basic stochastic process models. The amount of motion of the center of pressure decreased with increments of age from 3 to 5 years to young adult but increased again in the elderly age group. The availability of vision decreased the amount of motion of the center of pressure in all groups except the 3-year-old group, where there was less motion of the center of pressure with no vision. The stochastic properties of the center-of-pressure dynamic were assessed using both a two-process, random-walk model of Collins and De Luca and an Ornstein-Uhlenbeck model that is linear and has displacement governed only by a single stiffness term in the random walk. The two-process open- and closed-loop model accounted for about 96% and the Ornstein-Uhlenbeck model 92% of the variance of the diffusion term. Diffusion parameters in both models showed that the data were correlated and that they varied with age in a fashion consistent with developmental accounts of the changing regulation of the degrees of freedom in action. The findings suggest that it is premature to consider the trajectory of the center-of-pressure as a two-process, open- and closed-loop random-walk model given that: (a) the linear Ornstein-Uhlenbeck dynamic equation with only two parameters accommodates almost as much of the variance of the random walk; and (b) the linkage of a discontinuity in the diffusion process with the transition of open- to closed-loop processes is poorly founded. It appears that the nature of the stochastic properties of the random walk of the center-of-pressure trajectory in quiet, upright standing remains to be elucidated.

The dynamics of resting and postural tremor in Parkinson's disease.

OBJECTIVE The study examines the time and frequency structure of Parkinsons disease tremor in patients that exhibit no clinical signs of tremor. METHODS Eight mild to moderate Parkinsons disease and 8 matched control subjects maintained their limb in a constant position (30 s) under a postural finger, postural hand and resting tremor condition. Finger acceleration from the middle phalange, electromyographic (EMG) activity from extensor digitorum communis and flexor digitorum superficialis (FDS) were recorded. RESULTS The data confirmed that there were no differences in the amount of limb motion and the modal frequency was around 9 Hz for each subject group. The time-dependent organization of tremor was more regular (lower approximate entropy [ApEn]) in Parkinsons disease. Both time and frequency analyses between the acceleration and extensor EMG signals demonstrate a reduction in the 20-25 Hz tremor component and an increase in the 8-12 Hz region of tremor. CONCLUSIONS The results are discussed in relation to the proposal that increased regularity results from an increase in motor unit synchronization at 8-12 Hz and a reduction in the amplitude of the 20-25 Hz tremor component. The time and frequency structure of tremor may be useful in assessing individuals with Parkinsons disease.

Differential rate of recovery in athletes after first and second concussion episodes.

OBJECTIVE Clinical observations suggest that a history of previous concussions may cause a slower recovery of neurological function after recurrent concussion episodes. However, direct examination of this notion has not been provided. This report investigates the differential rate of restoring the visual-kinesthetic integration in collegiate athletes experiencing single versus recurrent concussion episodes. METHODS One hundred sixty collegiate athletes were tested preseason using multimodal research methodology. Of these, 38 experienced mild traumatic brain injury (MTBI) and were tested on Days 10, 15, and 30 after injury. Nine of these MTBI patients experienced a second MTBI within 1 year after the first brain injury and were retested. The postconcussion symptoms checklist, neuropsychological evaluations, and postural responses to visual field motion were recorded using a virtual reality environment. RESULTS All patients were asymptomatic at Day 10 of testing and were cleared for sport participation based on clinical symptoms resolution. Balance deficits, as evident by incoherence with visual field motion postural responses, were present at least 30 days after injury (P < 0.001). Most importantly, the rate of balance symptoms restoration was significantly reduced after a recurrent, second concussion (P < 0.001) compared with those after the first concussion. CONCLUSION The findings of this study confirm our previous research indicating the presence of long-term residual visual-motor disintegration in concussed individuals with normal neuropsychological measures. Most importantly, athletes with a history of previous concussion demonstrate significantly slower rates of recovery of neurological functions after the second episode of MTBI.

Effects of aging on force variability, single motor unit discharge patterns, and the structure of 10, 20, and 40 Hz EMG activity.

The purpose of this investigation was to examine the discharge properties of single motor units and the structure of the rectified 10, 20, and 40 Hz electromyographic (EMG) activity to determine a physiological correlate for the greater force variability with aging. Young (n=10; mean: 22+/-1 years), old (n=10; mean: 67+/-2 years), and older-old (n=10; mean: 82+/-5 years) adult humans produced isometric second finger abduction force in both constant and sine-wave tasks at 5, 10, 20, and 40% of their maximal voluntary contraction. Force and fine-wire intramuscular electromyography were recorded from the first dorsal interosseous muscle. The amount and time-dependent structure of the discharge rate variability of single motor units and Fourier analysis of the rectified intramuscular EMG was performed. Force output variability increased across the young, old, and older-old groups. The amount and time-dependent structure of the discharge rate variability of single motor units did not differ between the young and aging groups. There was a progressive decrease in the relative power of approximately 40 Hz EMG activity from the young>old>older-old subjects across the 5, 10, 20, and 40% maximum voluntary contraction (MVC) force levels. There was also a progressive increase in the relative power of the approximately 10 Hz EMG activity from young<old<older-old subjects at each target force level. The findings showed that a shift in the relative contribution of approximately 40 Hz to approximately 10 Hz neural activity is related to the reduced capacity of older adults to maintain optimal force control.