Biomedical subjects

K M Newell

Publications and source records attributed to K M Newell.

At least 19 recordsLinked to original sources

PubMed2001

Intermittency in the visual control of force in Parkinson's disease.

Studies on the variability of motor output in Parkinson's disease have found contrasting results depending on the speed-accuracy constraints of the task. The first goal of this study was to determine if Parkinson's disease subjects are more variable than control subjects. The second goal of the study was to examine the limitations on visual and motor processing that contribute to the changes in force variability in Parkinson's disease. Eight mild to moderate Parkinson's disease (age: 68-80 years) and eight matched control (age: 68-80 years) subjects maintained a constant level of force at 25% of their maximum voluntary contraction with their index finger and thumb (grip precision task) for 20 s while online visual feedback of the total force was viewed on a computer monitor. During the force task, subjects received visual feedback at varying frequencies. The sampled visual feedback levels were presented at intervals as slow as every 5 s to as fast as every 0.04 s (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, 25.6 Hz). Force variability decreased over sampled visual feedback according to hyperbolic decay functions. The minimal visual processing time for both the Parkinson's disease and control subjects was approximately 160 ms. Motor output corrections were generated in both groups at a frequency of 1 Hz over a wide range of sampled visual feedback levels. However, the amplitude of the 1-2 Hz visuo-motor corrective process was amplified in Parkinson's disease, and this related to increases in force-output variability. The findings suggest that the basal ganglia are important for adjusting the amplitude of motor output at 1-2 Hz during visuo-motor feedback control.

Aged↗

PubMed2001

Age differences in noise and variability of isometric force production.

This study examined whether age-related improvements observed in the motor performance of children result from a reduction of noise in the output of the sensori-motor system. Children ages 6, 8, and 10 years and young adults (N = 48, 12 per group) performed continuous, constant isometric force contractions with the index finger at four different force levels with and without visual feedback. The results revealed that: (a) performance improved with increases in age, (b) the force output signal exhibited increased irregularity and a more broadband frequency profile with increases in age under conditions with feedback, and (c) there were no age differences in the irregularity of the force signal and smaller age differences in the frequency profiles under conditions without feedback. It is proposed that the age-related enhancements in performance throughout childhood are primarily due to a more appropriate mapping of the organization of the sensori-motor system to the task constraints rather than to reduction of system noise.

Adolescent↗

PubMed2001

Visual control of isometric force in Parkinson's disease.

The current article reports an investigation of the influence of visual feedback on force production in Parkinson's disease (PD) that required subjects to maintain a constant amount of isometric force with their index finger and thumb with and without visual feedback. Eight PD and eight matched control subjects produced force at 5, 25 and 50% of their maximal voluntary contraction for 20 s. In conditions of full vision, the force trajectory and force target were viewed on the computer monitor. In the no visual feedback condition, visual feedback of the force trajectory vanished after the initial 8 s of the trial. The results showed that under the vision condition PD subjects produced levels of maximal and submaximal force that were similar to controls. Approximately 1.5-2.5 s following the removal of visual feedback, the force level in both subject groups decreased to steady-state levels. There was no difference in the time between visual feedback removal and the beginning of force decay in PD. There was a larger amount and faster rate of force decay after visual feedback removal in PD subjects compared to the controls. It is proposed that the increased force decay in PD does not result from sensory reflex deficits but from higher order sensory-motor memory processes.

Aged↗

PubMed2001

Postural coordination patterns as a function of dynamics of the support surface.

The present study investigated the compensatory postural coordination patterns that emerge in the face of dynamic changes in the surface of support. Adult subjects stood on a moving platform that was sinusoidally translated in the anterior-posterior direction. The frequency and amplitude of the support surface translation were manipulated over a wide range of parameter values. The results revealed that as the frequency of platform motion increased, the postural system systematically exploited the available joint-space degrees of freedom and generated four distinct postural coordination modes (a rigid mode --> ankle mode --> ankle-hip mode --> ankle-hip-knee mode). It appears that upright standing posture has a small set of coordination patterns that are particular to the dynamics of the surface of support.

Adult↗

PubMed2001

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 Bernstein's 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.

Adult↗

PubMed2001

Regularity of force tremor in Parkinson's disease.

OBJECTIVES: The study examines the time-dependent structure of force tremor to investigate two hypotheses: (1), the regularity of tremor can help in discriminating normal aging from that of Parkinson's disease (PD); and (2), there is increased tremor regularity with increases in the severity of PD. METHODS: Eight young (21-29 years), eight elderly (68-80 years), and eight PD (68-80 years) subjects produced constant grip force at 5, 25 and 50% of their maximal voluntary contraction by squeezing two load cells with their index finger and thumb under a vision and no vision condition. Spectral analysis and approximate entropy (ApEn) were used, respectively, to analyze the frequency and time-dependent structure of tremor. RESULTS: The analyses showed that there were no differences in the amplitude and modal frequency of force tremor between groups. The ApEn was significantly lower in the PD group compared with the controls. For the PD group, the linear relations between the total scores taken from the Unified Parkinson's Disease Rating Scale-motor section and the dependent variables were r(2)=0.71 (P<0.01) for ApEn, r(2)=0.20 (P>0.05) for the modal frequency, and r(2)=0.23 (P>0.05) for the standard deviation. Surrogate analyses revealed that the time-dependent structure of tremor provided additional information beyond that of amplitude and modal frequency analyses. CONCLUSIONS: These findings indicate that tremor analyses should not be limited to just the frequency and amplitude of the oscillation, and that the time-dependent structure of tremor is useful in differentiating tremor in healthy people from those with PD. The hypothesis that more regular tremor in PD is due to a loss of multiple neuronal oscillators contributing to the tremor output is discussed.

Adult↗

PubMed2001

The changing effector pattern of tardive dyskinesia during the course of neuroleptic withdrawal.

Tardive dyskinesia (TD) is a movement disorder that can be expressed at various body effector points, including the face, neck, arms, fingers, legs, and torso. In this prospective longitudinal study researchers examined whether the effector pattern of TD changed during the course of neuroleptic medication withdrawal in adults with mental retardation. Results indicated that the effector pattern of TD changed over the course of neuroleptic withdrawal. Peak dyskinesia was associated with the involvement of more body areas relative to baseline. Although dyskinesia decreased at follow-up and fewer body areas showed signs of dyskinesia, there were still differences in the effector pattern of dyskinesia relative to baseline at periods of 1 to 2 years following neuroleptic withdrawal. These findings suggest that TD is a dynamic disorder associated with changes in both severity and effector pattern over time.

Adolescent↗

PubMed2001

Risk factors for tardive dyskinesia in a large population of youths and adults.

This study was designed to identify predisposing factors for tardive dyskinesia (TD) in youths and adults within a large, predominantly developmentally disabled and mentally ill population. The findings support previously reported risk factors for TD, including increasing age, use of anticholinergic medication for those over 40 years old, and long duration of neuroleptic exposure for those over 18 years of age. Higher cumulative levels of "typical" neuroleptic dosage decreased the risk for TD for those over 18. Novel findings included the benefit of personality disorder in individuals 18 to 40 years old and the strong risk factor of profound mental retardation in all age groups. These findings reveal further complex interactions to the risk factors for TD.

Adolescent↗

PubMed2001

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 system's 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.

Cognition↗

PubMed2001

Stereotypy and motor control: differences in the postural stability dynamics of persons with stereotyped and dyskinetic movement disorders.

We examined whether dynamic measures of postural stability differentiated persons with stereotyped movement disorder from persons with dyskinetic movement disorder. Participants from three groups (stereotypy, dyskinesia, control) were given a goal-oriented postural stability task, and performance was measured using a force platform and computerized posturographic techniques. The results showed that both movement disorder groups differed from the control group in the posture task. Further, the stereotypy and dyskinesia groups demonstrated markedly different postural movement profiles. The postural motion of the stereotypy group was characterized by greater amplitude and variability but lower complexity than the dyskinesia group. These results provide support for a motor control model of stereotypy.

Adult↗

PubMed2000

Body scaling of grip configurations in children aged 6-12 years.

This study examined the influence of body scale on the grip configurations used by young children (6-12 years old) to displace cubes that varied systematically in size (L) and mass (M). It was determined if the scaling relation we had developed for adults K = log Lc + ((log Mc)/(a + bLh + cMh)) where L(c) and M(c) is the length side and mass of the cubes, respectively, and L(h) and M(h) are the length and mass of the hand, respectively, it would also predict the change in grip configurations across this age range in a fashion consistent with the principle of similitude. The statistical and scaling analyses revealed that the invariant body-scaled relation that specified the adult grip transitions also held for the 6- to 12-year-old children.

Adult↗

PubMed2000

Assessment of the adiabatic transformability hypothesis in a ball-bouncing task. mbrodel@freewwweb.com.

The adiabatic transformability hypothesis for non-conservative, non-rate-limited biological systems put forward by Kugler and Turvey [Kugler PN, Turvey MT (1987) Information, natural law, and the self-assembly of rhythmic movements, Erlbaum, Hillsdale, NJ] is evaluated in a ball-bouncing task as a function of skill level. We hypothesized that, when a basketball player increases or decreases the frequency of his limb motion in a vertical ball-bouncing task, the transformation should be characterized as adiabatic. Confirmation of this hypothesis would lend support to the body of knowledge that suggests that physical-biological laws guide the behavior of people engaged in motor tasks, including their acquisition of skill. We videotaped and analyzed four participants - two intermediates and two experts - bouncing a ball from various heights, and measured the energy and kinematic relations of the ball and the participants' body segments. The task presents a challenge to certain predictions of the adiabatic hypothesis in evaluating changes in movement velocity (v) or frequency (f), and energy as adiabatic transformations. Among these are the constant relation between kinetic energy (Ek) per cycle and v, constancy of energy dissipated per cycle (Et) over changes in v and Ek, the ratio of Ek to Et per cycle (the "Q" values), and the relation of amplitude to v. From our observations, which are examined in regard to the insights of Kugler and Turvey about the relation of Ehrenfest's adiabatic theorem to biological systems, we confirm the basic adiabatic character of the task in analyzing both the ball alone and the relations of various body segments. In the segmental frame of reference, we found evidence of differences in energy-kinematic relations in the Q values between skill levels.

Adult↗

PubMed2000

Amplitude changes in the 8-12, 20-25, and 40 Hz oscillations in finger tremor.

OBJECTIVE: The study examined the amplitude and frequency modulation of the 8-12, 20-25, and 40 Hz frequencies of tremor to determine the degree to which increments of load affect the amplitude of these neural rhythms. METHODS: Finger acceleration from the middle phalange and electromyographic (EMG) activity of the extensor digitorum communis (EDC) muscle were recorded on 10 normal adult subjects. Two experiments are reported that manipulated loads ranging from 0 to 40 and 0 to 200 g that were attached to the distal portion of the outstretched middle phalange. RESULTS: There were 8-12, 20-25, and 40 Hz oscillations in the EMG recording but only the 8-12 and 20-25 Hz rhythms were present in the tremor and tremor-EMG coherence. Adding load to the finger reliably decreased the 20-25 Hz band of acceleration, reduced the relative power within the 20-25 Hz EMG band, increased the relative power of the 40 Hz band, but had no effect on the relative power within the 8-12 Hz EMG frequency band. The tremor-EMG coherence in the 8-12 and 40 Hz regions was independent of load, but was markedly reduced with load in the 20-25 Hz band. CONCLUSIONS: The 8-12, 20-25, and 40 Hz neural rhythms of physiological tremor have a stable frequency consistent with central oscillations. There is an increase in the relative power of the 40 Hz EMG band with force, but only the amplitude of the 20-25 Hz band is modulated by mechanical-reflex feedback.

Adolescent↗

PubMed2000

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

OBJECTIVE: The study examines the time and frequency structure of Parkinson's disease tremor in patients that exhibit no clinical signs of tremor. METHODS: Eight mild to moderate Parkinson's 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 Parkinson's 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 Parkinson's disease.

Aged↗

PubMed2000

Postural and resting tremor in the upper limb.

OBJECTIVE: Tremor from multiple segments of the upper limb was recorded under postural and resting conditions. The aims of this study were to examine the nature of tremor within a single limb segment, intra- and inter-limb co-ordination of tremor, and the influence of cardiac mechanical events on physiological tremor. METHODS: Tremor was recorded from eight healthy adult subjects during a postural pointing task where the level of support for the upper limb segments was successively increased. The dynamics of tremor within a single segment were examined using power spectral, ApEn and amplitude analyses. Inter-segment tremor relations were determined using coherence and Cross-correlation analyses. RESULTS: Single segment analysis demonstrated that each (unsupported) limb segment contained two major frequency peaks (at 1-4 Hz and 8-12 Hz). Both peaks were still evident in the distal segments when the proximal segments were supported. External support of the more proximal limb segments also resulted in decreased finger tremor, but these changes were not simply additive over segments within a limb or equal across fingers. There were significant relations between adjacent proximal and distal limb segment pairs but no correlations between contralateral limb segments or between heart rate and limb tremor. CONCLUSIONS: These findings imply that: the low frequency component (1-4 Hz) of physiological tremor in the hand and finger could not be attributed to passive transmission of oscillations from the upper arm and forearm; and the contribution of proximal segments on tremor in the index finger tremor could not be predicted from mechanical principles alone. The minimization of finger tremor involved compensatory coupling of segments of the upper arm with particular emphasis upon active control of the wrist joint.

Acceleration↗

PubMed2000

Body-scaled transitions in human grip configurations.

This article reports two experiments that were set up to examine the preferred human grip configuration used to displace cubes that varied in length (Lc), mass (Mc), and density (ML3). In particular, the authors sought to provide a more precise test of a dimensional relation between the object and the hand that had previously been shown to predict the grip configuration used to transport an object from one location to another. The experiments examined 2 grip transitions (from 3 digits to 4 digits and from 1 hand to 2 hands) within 2 sets of object conditions. In Experiment 1, cubes with a low density and a small increment in size (1 mm) were used, whereas in Experiment 2, cubes with 2 fixed sizes and small increments in mass were used. The results showed that the body-scaled equation K = logLc + (logMc/a + bMh + cLh), where Mh and Lh are the anthropometric measures of the hand mass and length and a, b, and c are empirical constants, is the body-scaled information that predicts the grip configurations used to displace objects.

Adult↗

PubMed2000

Coordination of grip configurations as a function of force output.

In this investigation, the authors examined the coordination and control of force production by the digits of the hand as a function of criterion force level and grip configuration. Each adult participant (N = 6: 3 men and 3 women) was required to place the thumb and a finger (or fingers) upon load cells that were fixed to a grasping apparatus that was clamped to a table. In the task, participants had to match a criterion continuous constant total force level displayed on a computer screen. There were 10 trials at each grip configuration and criterion force level combination on each of 3 consecutive days. The results showed that (a) different grip configurations minimized error at each force level; (b) there was a specific digit pairing within a given grip configuration that produced the highest correlation of force output; (c) the correlation between the force output of digits generally increased at higher force levels; (d) error was reduced at each force level and grip configuration over the practice period; and (e) the organization of the force output of each digit varied as a function of digit, force level, grip configuration, and practice. The findings are consistent with the hypothesis that coordination of the digits in prehension is reflective of an adaptive, task-specific solution that is modified with practice.

Adult↗

PubMed2000

Variability and noise in continuous force production.

In the present 3 experiments, the authors examined the hypothesis, derived from information theory, that increases in the variability of motor responses result from increases in perceptual-motor noise. Three different groups of participants (Ns = 10, 9, and 10, respectively, in Experiments 1, 2, and 3) produced continuous isometric force under either low, intermediate, or high target force levels. When considered together, the results showed that force variability (SD) increased exponentially as a function of force level. However, an index of information transmission (M/SD), as well as measures of noise in both the time (approximate entropy) and the frequency (power spectrum) domains, changed according to an inverted-U-shaped function over the range of force levels. The findings provide further evidence that increased information transmission is related to increases, and not to decreases, in the noisiness of the structure of force output.

Adolescent↗