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Karl M Newell

Publications and source records attributed to Karl M Newell.

At least 19 recordsLinked to original sources
PubMed2004

Intra-limb segmental influences on random-like movements in humans.

The experiment investigated the influence of segmental coupling on the ability to produce random-like movements in individual limb segments. Adult participants were instructed to move randomly (2 min trials) in the sagittal plane their index finger, hand, and lower arm as "frozen" effector units or where the individual links within the upper limb complex were free to move independently. The findings showed that the distal finger movements were more random-like when the proximal joints were also free to vary, but the reverse directional segmental effects were not present. Analysis of the movement frequency structure of the coordination between limb segments showed that patterns of modal frequencies were preserved even though the participants were trying to produce with equal probability a wide range of frequencies. These findings provide further evidence that: (1) the boundary conditions on the degrees of freedom of the neural output of an effector are relatively restrictive; (2) inter-limb reactive forces can enhance the limits on the dynamical degrees of freedom; and (3) the intrinsic dynamics influence movement output even when the task goal is a random output.

Adult↗
PubMed2004

Task goal and grip force dynamics.

This study examined the effect of task goal on the structure of isometric force variability during precision grasping. In general, variability of isometric force production decreases when participants are asked to maintain a particular force output and are provided with visual feedback, although the irregularity of force output tends to increase under these conditions. In the current study we compared the tasks of holding an object using a precision grip and holding an object using a precision grip while matching a force target. Adults held an object between the index finger and thumb and force output was measured using load cells. The mass (92, 276, 460 g) and the grip aperture (5.5 and 8.5 cm) of the object were varied producing six different object conditions. The goal of the task was to either: (a) hold the object comfortably in a stable position (holding task) or (b) hold the object comfortably in a stable position while maintaining a constant target force level that matched the grip force of the holding condition (target task). The results showed that the amount of force variability in the target condition was lower than during the holding condition, while the force output was more regular in the holding condition. Increments in object mass increased force regularity in the holding condition whereas increments of force level decreased regularity in the target condition. The level of coherence between the two digits was very high (approximately 0.98) and maximum coherence occurred at a higher frequency during the target (0.94 Hz) as opposed to the holding (0.70 Hz) condition. The findings reveal that the goal of the task can qualitatively change the dynamical organization of the force output in prehension, even when the average force level produced is the same. This effect on the control strategy was mediated by visual information processes that interact with level of force output in determining the structure of variability. Theorizing about the organization of isometric force output should include the effects of task goals as well as the level of force per se.

Adult↗
PubMed2004

Upper-extremity interlimb coupling in persons with left hemiplegia due to stroke.

OBJECTIVE: To investigate interlimb coupling in an adult population with left hemiplegia and an age-matched control group to better understand the unique motor control issues in stroke rehabilitation. DESIGN: A chi-square analysis was performed to compare the distribution of participants adopting a given movement pattern ratio during 2 different bimanual movement tasks for both groups. The task involved oscillating the upper limbs at the elbow in asymmetric patterns, with 1 limb oscillating at twice the frequency of the other. SETTING: Testing was done in the subjects' residences or in an outpatient clinic. PARTICIPANTS: Participants were between the ages of 45 and 75 years (mean +/- standard deviation, 63+/-9.4y), right handed, and included 18 left hemiparetic and 18 control subjects. Selection criteria for the hemiparetic group included status after nonhemorrhagic stroke within the distribution area of the right middle cerebral artery (RMCA). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Relative phase of the upper extremities. RESULTS: The hemiplegic group produced predominantly an in-phase 1-to-1 movement pattern, whereas the control group exhibited antiphase, 2-to-1 movement harmonics and, to a lesser extent, in-phase movement patterns. CONCLUSIONS: This study suggests that brain damage caused by stroke in the RMCA distribution area results in the reduction of selectable interlimb movement patterns. Specifically, bimanual upper extremity movement tended to be highly coupled in an in-phase movement pattern. Research is needed to examine the ability of stroke survivors to learn bilateral upper-extremity tasks at less stable levels of interlimb coupling.

Aged↗
PubMed2004

Perceived effort in force production as reflected in motor-related cortical potentials.

OBJECTIVE: The perceived effort in force production was investigated in a series of experiments where subjects performed isometric force tasks with the index finger while the nominal force, the rate of force development and signal gain were controlled and rating of effort for each task was obtained. The hypotheses tested were that: (1) force-related perceived effort may selectively influence the amplitude of motor-related cortical potentials (MRCP); and (2) the MRCP may directly reflect the intensity of perceived effort associated with force production. METHODS: The force trace was displayed on a computer monitor using various control-gains so that the perceived effort matched or was at odds with actual muscular effort applied to the load cell to accomplish the task. The MRCP were extracted from continuous EEG records using averaging techniques. RESULTS: The findings showed that: (1) perceived effort proportionally increased with the increment of rate of force development and force error, but not with the actual force level; (2) the amplitude of the MRCP increased when a large amount of force was accompanied by an increased rate of force development; (3) the amplitude of early components of MRCP preceding the force initiation (MP-100 to 0) increased as a function of anticipated effort, whereas, the amplitude movement-monitoring potentials (MMP) accompanying the force production increased as a function of actual force level. CONCLUSIONS: The findings from this study provide additional insight clarifying the distinct patterns of EEG activity exhibited under various degrees of perceived effort associated with force output. The findings support the hypothesis that the early components of MRCP may reflect the perceived effort associated with achieving the required force level. SIGNIFICANCE: The results from this study may be considered in the larger context of physical activity in terms of importance of perceived effort during prescribed exercise in rehabilitation programs.

Adult↗
PubMed2004

Coordination changes in the early stages of learning to cascade juggle.

The experiment was setup to examine the coordination changes in assembling the movement form of 3-ball cascade juggling. Eight adult participants learned to juggle over 4 weeks of practice. Juggling scores were recorded at each session and performance was videotaped at eight selected sessions for purposes of movement analysis. Once the basic spatial and temporal constraints on cascade juggling were satisfied, and the figure-8 juggling mode was established, temporal modulations of the relative motions of the hands were emphasized. All participants learned to juggle and the increase over practice in the number of consecutive balls caught was best fit with a power law. The non-proportional rate of performance increment was consistent with the qualitative changes in the form of the hand and ball movement kinematics that occurred over practice.

Adult↗
PubMed2004

Changes in the structure of children's isometric force variability with practice.

This study examined the effect of age and practice on the structure of children's force variability to test the information processing hypothesis that a reduction of sensorimotor system noise accounts in large part for age-related reductions in perceptual-motor performance variability. In the study, 6-year-olds, 10-year-olds, and young adults practiced on 5 consecutive days (15 trials/day), maintaining for 15-s trials a constant level of force (5 or 25% of maximum voluntary contraction) against an object using a pinch grip (thumb and index finger). With increasing age, the amount of force error and variability decreased, but the sequential structure of variability increased in irregularity. With practice, children reduced the amount of variability by changing the structure of the force output so as to be more similar to that of their older counterparts. The findings provide further evidence that practice-driven changes in the structure of force output, rather than a decline in the amount of white noise, largely account for age-related reductions in the amount of force variability.

Adult↗
PubMed2003

Aging and rhythmical force output: loss of adaptive control of multiple neural oscillators.

The current study examined the influence of aging on the oscillatory activity of a population of motor units during rhythmical force production. Previously, it has been shown that aging humans have greater low-frequency and less high-frequency electromyographic (EMG) activity during constant and slow ramp force contractions. We hypothesized that more rapid force contractions would reverse the established finding of reduced high- and greater low-frequency EMG activity to greater high- and reduced low-frequency EMG activity in older adults. Intramuscular EMG activity and effector force were recorded while 45 human subjects (20-31 and 60-88 yr of age) rhythmically produced force at four distinct frequencies (1-4 Hz) and two force levels (5 and 25% maximal voluntary contraction). Spectral and coherence analyses were performed on the force output and EMG activity. In the 3- and 4-Hz targets, the older adults had greater 35- to 50-Hz and reduced 0- to 5-Hz EMG activity compared with the young adults. There was greater EMG-force coherence in the 0- to 5-Hz bandwidth for the young subjects. No systematic age difference in the phase relationship between the EMG and force signals were found. Higher frequency force contractions reversed the previously established aging differences in the relative contribution of low- and high-frequency EMG activity. Thus the frequency properties of the task goals channel the relative contribution of low and high EMG activity. Furthermore, it is proposed that aging humans lose the adaptive capability to coordinate the excitatory and inhibitory activity of multiple neural oscillators.

Adaptation, Physiological↗
PubMed2003

Deterministic and stochastic processes in children's isometric force variability.

This study examined the influence of deterministic and stochastic processes (including white Gaussian noise) on reductions in the amount of force output variability through childhood. The structure of the force signal produced during a constant isometric pinch grip task was examined as a function of age (6, 8, and 10 years, and young adults), availability of feedback information (with and without vision), digit (thumb and index finger), and force level (5, 15, 25, and 35% of maximal voluntary contraction). The amount of white Gaussian noise in the force signals was negligible and not age related. The availability of vision led increasingly over the older age groups to lower long-range correlations with more than a single scaling range in a 1/f-like decay process. The reductions in the amount of force variability from childhood to adulthood were related in large part to deterministic organization that increased the adaptive use of higher frequency components, due to the more flexible use of information feedback and feedforward processes.

Analysis of Variance↗
PubMed2003

Learning to coordinate redundant degrees of freedom in a dynamic balance task.

The present study investigated Bernstein's [The co-ordination and regulation of movements, 1967] proposal regarding the three stages of learning in the changing coordination and control of redundant joint-space degrees of freedom. Six participants practiced maintaining balance on a moving platform that was sinusoidally translated in the anterior-posterior direction for 30 trials on day 1 and 10 trials on day 2. At the beginning of practice, the motion of the torso and limb segments was less coherent in the attempt to compensate for the movement of the support surface in retaining a balanced posture. However, with practice, the organization of a compensatory postural coordination mode became highly coherent and also progressively utilized the passive, inertial forces generated by the movement of the support surface. The findings support the propositions that: (a) the pathway of change over time in the coordination pattern of the torso and joint motions depends on the task goal and constraints to action and (b) the changes in limb and torso motion are in support of the learning of a global body center of mass/platform dynamic.

Adult↗
PubMed2003

Attentional focus influences the walk-run transition in human locomotion.

This study tested the hypothesis that cognitive perceptual processes are involved in determining the walk-run transition in human locomotion. In a dual-task paradigm, 12 healthy male participants (aged 21.8+/-2.4 years) walked and ran on a treadmill while solving mental arithmetic (MA) organized in two levels of difficulty (easy and hard). Speed was increased over seven increments of 0.1 ms(-1) while the walk-run transition speed (TS) and central and peripheral ratings of perceived exertion (RPE) were recorded. MA performance was maintained between control (no locomotion) and treadmill conditions and participants rated hard MA as more difficult and more mentally engaging than easy MA. The TS increased during both levels of MA, although RPE values did not reflect psychological attenuation across the transition. Together, these results support the hypothesis that cognitive load distracts attentional focus from physiological cues that contribute to triggering human gait transitions.

Adult↗
PubMed2003

Task goals and change in dynamical degrees of freedom with motor learning.

In this article, the authors examined the hypothesis that the direction of the change (increase or decrease) in the dynamical degrees of freedom (dimension) regulated as a function of motor learning is task-dependent. Adult participants learned 1 of 2 isometric force-production tasks (Experiment 1: constant force output; Experiment 2: sinusoidal force output) over 5 days of practice and a 6th day with augmented information withdrawal. The results showed that over practice, the task goal induced either an increase (Experiment 1) or a decrease (Experiment 2) in the dimension of force output as performance error was reduced. These findings support the proposition that the observed increase or decrease in dimension with learning is dependent on both the intrinsic dynamics of the system and the short-term change required to realize the task goal.

Adaptation, Physiological↗
PubMed2003

Beyond curve fitting: a dynamical systems account of exponential learning in a discrete timing task.

The authors examined the function for learning a discrete timing task from a dynamical systems perspective rather than solely the traditional curve-fitting viewpoint. Adult participants (N = 8) practiced a single-limb angular movement task of 125 ms over 20 degrees for 200 trials. There was no significant difference in percentage of variance accounted for in 3 parameter exponential and power-law nonlinear fits to the individual and averaged data. The percentage of variance increased in both exponential and power-law equations when the data were averaged over participants and trials. Drawing on a dynamical systems approach to time scales in motor learning and on analysis of the distinctive features of exponential and power-law functions, however, the authors conclude that the exponential is the learning function for that task and that level of practice.

Female↗
PubMed2003

Organization of compensatory postural coordination patterns.

The authors investigated whether compensatory postural coordination patterns are organized according to the same dynamical principles as are nonequilibrium phase transitions. Eight participants were asked to maintain upright balance on a moving platform that was sinusoidally translated in the anterior-posterior direction and was systematically increased and decreased 0.19 Hz as a step function every 10 platform cycles through the frequency range 0.19-1.46 Hz. At low platform frequencies, all participants exhibited small joint angular motions with high variability, and the relative phase between the joint motions exhibited drifting patterns and large fluctuations. As platform frequency increased, the amplitude of joint motion increased systematically and joint-specific oscillatory patterns emerged. The findings provided no evidence for a Hopf bifurcation or hysteresis in the transitions of postural coordination modes, however, or, more generally, a basis for distinguishing the relevance of linear versus nonlinear models of postural control.

Adult↗
PubMed2003

Schema theory (1975): retrospectives and prospectives.

A brief commentary is provided on the theoretical assumptions, scholarly impact and continuing influence of the schema theory of motor learning (Schmidt, 1975). The traditional contrasts of schema theory to the coordinative structure or dynamical systems framework are reemphasized, and limitations of the variability of practice experiments noted. A central problem for theories of motor learning is change over time, the basis on which learning is typically defined. Most theories including schema have, however, undervalued the importance of the time-dependent nature of change in deference to the almost exclusive study of the amount of some averaged change in behavioral outcome. The persistent and transitory change(s) in movement and outcome that are observed in action are reflections of multiple time scales of change in a dynamical system.

Humans↗
PubMed2003

Aging and the time and frequency structure of force output variability.

The present study examined the time and frequency structure of force output in adult humans to determine whether the changes in complexity with age are dependent on external task demands. Healthy young (20-24 yr), old (60-69 yr), and older-old (75-90 yr) humans produced isometric force contractions to constant and sine wave targets that also varied in force level. First, force variability on each force task increased with advancing age. Second, both time and frequency analysis showed that the structure of the force output in the old and older-old adults was less complex in the constant-force level task and more complex in the sine wave force task. Third, the alterations in force output with aging were primarily due to low-frequency bands <4 Hz. These results support the postulation that the observed increase or decrease in physiological complexity with aging is influenced by the relatively fast time scale of external task demands (Vaillancourt DE and Newell KM. Neurobiol Aging 23: 1-11, 2002).

Adult↗
PubMed2003

Direct fit of a theoretical model of phase transition in oscillatory finger motions.

This paper presents a general method to fit the Schöner-Haken-Kelso (SHK) model of human movement phase transitions directly to time series data. A robust variant of the extended Kalman filter technique is applied to the data of a single subject. The options of covariance resetting and iteration within recursion were used to obtain time-dependent estimates of both the alpha and beta parameters in the SHK model. Comparison between transition onset time and the time at which /beta(t/T)/alpha(t/T)/ becomes critical indicates that the transitions are advanced by noise. The method can be extended to handle non-normal data and generalization across subjects and/or experimental conditions.

Adult↗
PubMed2002

Children's coordination of force output in a pinch grip task.

This study examined the role of sensorimotor system noise in the organization of the force output of the thumb and index finger and the coordination between the two digits in an isometric pinch grip force task as a function of age (6, 8, 10, 18-22 years), feedback condition (with and without visual feedback information), and force level (5, 15, 25, and 35% of maximal voluntary force. With increases in age under the visual feedback conditions, the signal-to-noise ratio increased, the sequential structure of the force output signals became more irregular, the degree of coherence between the digits at higher force levels was enhanced, and the digits exhibited a greater degree of coherence across the higher frequencies of the power spectrum at all force levels. However, these age differences were either minimized or eliminated under conditions without feedback. These findings show that the age-related performance differences in grip force variability are primarily due to more effective use of visual information rather than age differences in intrinsic sensorimotor noise.

Adolescent↗