Biomedical subjects

Peter J Beek

Publications and source records attributed to Peter J Beek.

At least 19 recordsLinked to original sources

PubMed2006

Laterally focused attention modulates asymmetric coupling in rhythmic interlimb coordination.

Peters (J Motor Behav 21:151-155, 1989; Interlimb coordination: neural, dynamical and cognitive constraints, Academic, Orlando, pp 595-615, 1994) suggested that expressions of handedness in bimanual coordination may be reflections of an inherent attentional bias. Indeed, previous results indicated that focusing attention on one of the limbs affected the relative phasing between the limbs in a manner comparable to the effects of hand dominance. The present study extended the comparison between the effects of attentional focus and handedness by testing their impact on the interactions between the limbs. Both left-handed and right-handed participants performed rhythmic bimanual coordination tasks (in-phase and antiphase coordination), while directing attention to either limb. Using brief mechanical perturbations, the degree to which the limbs were influenced by each other was determined. The results revealed that the non-dominant limb was more strongly affected by the dominant limb than vice versa and that, in line with Peters' proposition, this handedness-related asymmetry in coupling strength was reduced when attention was focused on the non-dominant limb, thereby highlighting the potential relation between inherent (handedness-related) asymmetries and voluntary attentional asymmetries. In contrast to previous findings, the (commonly observed) phase lead of the dominant limb was attenuated (rather than accrued) when attention was focused on this limb. This unexpected result was explained in terms of the observed attention-related difference in amplitude between the limbs.

Adult↗

PubMed2006

Impedance modulation and feedback corrections in tracking targets of variable size and frequency.

Humans are able to adjust the accuracy of their movements to the demands posed by the task at hand. The variability in task execution caused by the inherent noisiness of the neuromuscular system can be tuned to task demands by both feedforward (e.g., impedance modulation) and feedback mechanisms. In this experiment, we studied both mechanisms, using mechanical perturbations to estimate stiffness and damping as indices of impedance modulation and submovement scaling as an index of feedback driven corrections. Eight subjects tracked three differently sized targets (0.0135, 0.0270, and 0.0405 rad) moving at three different frequencies (0.20, 0.25, and 0.33 Hz). Movement variability decreased with both decreasing target size and movement frequency, whereas stiffness and damping increased with decreasing target size, independent of movement frequency. These results are consistent with the theory that mechanical impedance acts as a filter of noisy neuromuscular signals but challenge stochastic theories of motor control that do not account for impedance modulation and only partially for feedback control. Submovements during unperturbed cycles were quantified in terms of their gain, i.e., the slope between their duration and amplitude in the speed profile. Submovement gain decreased with decreasing movement frequency and increasing target size. The results were interpreted to imply that submovement gain is related to observed tracking errors and that those tracking errors are expressed in units of target size. We conclude that impedance and submovement gain modulation contribute additively to tracking accuracy.

Adult↗

PubMed2006

Handedness-related asymmetry in coupling strength in bimanual coordination: furthering theory and evidence.

The effects of handedness on bimanual isofrequency coordination (e.g., phase advance of the dominant limb) have been suggested to result from an asymmetry in interlimb coupling strength, with the non-dominant limb being more strongly influenced by the dominant limb than vice versa. A formalized version of this hypothesis was tested by examining the phase adjustments in both limbs in response to mechanical perturbation of the bimanual coordination pattern and during frequency-induced phase transitions, for both right- and left-handed participants. In both situations, the phase adaptations were made predominantly by the non-dominant limb in right-handers, whereas this effect failed to reach significance in left-handers. Thus, the asymmetry in coupling strength was less pronounced in the latter group. In addition, the degree of asymmetry depended on movement frequency. The observed asymmetry was discussed in relation to pertinent neurophysiological findings.

Adult↗

PubMed2006

Bimanual coordination dysfunction in early, untreated Parkinson's disease.

Bimanual coordination involves the simultaneous performance of either symmetrical (in-phase) or asymmetrical (anti-phase) movements with both hands and is known to be impaired in Parkinson's disease (PD). At present, it is unclear whether this aspect of motor function is already impaired in early stage, untreated PD patients. Therefore, we investigated the accuracy of bimanual coordination in 13 early stage, untreated PD patients and 13 age- and sex-matched healthy controls. Each subject performed bimanual coordination tasks at two different movement frequencies (1 and 1.75 Hz) and with two different phase relationships (in-phase and anti-phase). The percentage of unsuccessful trials (as a measure of overall task performance) in PD patients was significantly higher than in healthy subjects. PD patients performed high frequency in-phase and anti-phase bimanual coordination tasks less accurately with their non-dominant hand than healthy subjects. Furthermore, PD patients had more difficulty than healthy subjects in maintaining a constant phase relationship between the hands in the anti-phase condition at low movement frequency. This study demonstrates that bimanual coordination dysfunction is a very early sign of PD. Bimanual coordination tasks, in particular those involving high frequency anti-phase movements, might prove useful in the early diagnosis of PD.

Aged↗

PubMed2006

Bilateral phase entrainment by movement-elicited afference contributes equally to the stability of in-phase and antiphase coordination.

This study examined if and how phase entrainment by movement-related afference-- induced by passive movements of the contralateral hand-- contributes to the coordinative stability of rhythmic bimanual movements. The results revealed that phase-shifted passive movements of the dominant or the nondominant hand induced similar entrainment effects on the active movements of the contralateral hand. In terms of the phase relations between the hands only two attractors of equal strength were present, corresponding to relative phase shifts of 0 degrees and 180 degrees , respectively, i.e., to in-phase and antiphase coordination. The attractors were separated by two repellors located at relative phase shifts of +90 degrees and -90 degrees . EMG analysis indicated that the entrainment effects indeed resulted from contralateral afference, because no related changes in muscle activation were observed in the passively moved hand. It was concluded that phase entrainment by contralateral afference contributed equally to the stable performance of the bimanual in-phase and antiphase patterns, thereby enhancing the stability of these patterns relative to other phase relations between the limbs.

Adolescent↗

PubMed2006

How do persons with chronic low back pain speed up and slow down? Trunk-pelvis coordination and lumbar erector spinae activity during gait.

In healthy walking, the timing between trunk and pelvic rotations, as well as erector spinae (ES) activity varies systematically with walking velocity, whereas a comparable velocity-dependent adaptation of trunk-pelvis coordination is often reduced or absent in persons with low back pain (LBP). Based on the hypothesis that trunk-pelvis coordination is linked to overall gait stability, persons with LBP can be expected to have difficulties in dealing with perturbations. We examined the ability of 12 persons with LBP and 12 controls to adapt trunk and pelvis rotations and ES activity to sudden changes in velocity. 3D angular movements of thoracic, lumbar, and pelvic segments and surface EMG were recorded during treadmill walking at six different velocities, which increased or decreased unexpectedly. Relative phases of segmental rotations were determined and (in-)variant properties of kinematics and ES activity were studied using principal component analysis. Compared to healthy controls, persons with LBP exhibited a reduced ability to adapt trunk-pelvis coordination and ES muscle activity to changes in velocity. Altered coordination and muscular control may reflect an attempt to stabilise the spine and prevent the occurrence of unexpected perturbations. The assessment of gait patterns in terms of coordination may help clinicians to quantify movement impairments and may suggest interventions aimed at facilitating the emergence of desired coordination patterns.

Acceleration↗

PubMed2006

Mechanical invariants are implicated in dynamic touch as a function of their salience in the stimulus flow.

The authors investigated the mechanical basis of length perception through dynamic touch using specially designed rods in which the various moments of mass distribution (mass, static moment, and rotational inertia) were varied independently. In a series of 4 experiments, exploration style and rod orientation were manipulated such that the relative salience of moments of mass distribution varied markedly. Results showed that perceived length was based on the most salient moments. The authors concluded that the notion of salience is crucial for understanding the implication of moments of mass distribution in length perception and that it should play a pivotal role in developing an encompassing theory of dynamic touch.

Adult↗

PubMed2006

Late information pick-up is preferred in basketball jump shooting.

In this study we examined the timing of optical information pick-up in basketball jump shooting using an intermittent viewing technique. We expected shooters to prefer to look at the basket as late as possible under the shooting style used. Seven experts with a high shooting style and five experts with a low shooting style took 50 jump shots while wearing liquid-crystal glasses that opened and closed at pre-set intervals. In principle, under this constraint, the participants could control when they saw the basket by actively modulating the timing of their movements. Analyses of the phasing of the movements relative to the events defined on the glasses revealed that low-style shooters preferred to see the basket just before the ball passed their line of sight, whereas high-style shooters tended to view the basket from underneath the ball after it passed their line of sight. Thus, most shooters preferred to pick up optical information as late as possible given the adopted shooting style. We conclude that, in dynamic far aiming tasks such as basketball jump shooting, late pick-up of optical information is critical for the successful guidance of movements.

Adolescent↗

PubMed2006

Intentional switches between bimanual coordination patterns are primarily effectuated by the nondominant hand.

Based on indications that hand dominance is characterized by asymmetrical interlimb coupling strength (with the dominant hand exerting stronger influences on the nondominant hand than vice versa), intentional switches between rhythmic bimanual coordination patterns were predicted to be mediated primarily by phase adaptations in the movements of the nondominant hand. This hypothesis was supported for both right-handed and left-handed participants who performed voluntary switches from in-phase to antiphase coordination and vice versa, at four different frequencies. In accordance with previous indications that handedness is expressed less consistently in left-handers, the asymmetry between the hands was less pronounced in left-handed than in right-handed participants. The asymmetry was smaller for switches from in-phase to antiphase coordination (i.e., in the direction opposite to spontaneous transitions) than for switches in the reverse direction, suggesting that (the expression of) the handedness-related asymmetry in coupling strength was weakened by intentional processes associated with these switches.

Adolescent↗

PubMed2005

Deterministic and stochastic features of rhythmic human movement.

The dynamics of rhythmic movement has both deterministic and stochastic features. We advocate a recently established analysis method that allows for an unbiased identification of both types of system components. The deterministic components are revealed in terms of drift coefficients and vector fields, while the stochastic components are assessed in terms of diffusion coefficients and ellipse fields. The general principles of the procedure and its application are explained and illustrated using simulated data from known dynamical systems. Subsequently, we exemplify the method's merits in extracting deterministic and stochastic aspects of various instances of rhythmic movement, including tapping, wrist cycling and forearm oscillations. In particular, it is shown how the extracted numerical forms can be analysed to gain insight into the dependence of dynamical properties on experimental conditions.

Forearm↗

PubMed2005

Impedance is modulated to meet accuracy demands during goal-directed arm movements.

The neuromuscular system is inherently noisy and joint impedance may serve to filter this noise. In the present experiment, we investigated whether individuals modulate joint impedance to meet spatial accuracy demands. Twelve subjects were instructed to make rapid, time constrained, elbow extensions to three differently sized targets. Some trials (20 out of 140 for each target, randomly assigned) were perturbed mechanically at 75% of movement amplitude. Inertia, damping and stiffness were estimated from the torque and angle deviation signal using a forward simulation and optimization routine. Increases in endpoint accuracy were not always reflected in a decrease in trajectory variability. Only in the final quarter of the trajectory the variability decreased as target width decreased. Stiffness estimates increased significantly with accuracy constraints. Damping estimates only increased for perturbations that were initially directed against the movement direction. We concluded that joint impedance modulation is one of the strategies used by the neuromuscular system to generate accurate movements, at least during the final part of the movement.

Adult↗

PubMed2005

Can co-activation reduce kinematic variability? A simulation study.

Impedance modulation has been suggested as a means to suppress the effects of internal 'noise' on movement kinematics. We investigated this hypothesis in a neuro-musculo-skeletal model. A prerequisite is that the muscle model produces realistic force variability. We found that standard Hill-type models do not predict realistic force variability in response to variability in stimulation. In contrast, a combined motor-unit pool model and a pool of parallel Hill-type motor units did produce realistic force variability as a function of target force, largely independent of how the force was transduced to the tendon. To test the main hypothesis, two versions of the latter model were simulated as an antagonistic muscle pair, controlling the position of a frictionless hinge joint, with a distal segment having realistic inertia relative to the muscle strength. Increasing the impedance through co-activation resulted in less kinematic variability, except for the lowest levels of co-activation. Model behavior in this region was affected by the noise amplitude and the inertial properties of the model. Our simulations support the idea that muscular co-activation is in principle an effective strategy to meet accuracy demands.

Biomechanical Phenomena↗

PubMed2005

Unraveling interlimb interactions underlying bimanual coordination.

Three sources of interlimb interactions have been postulated to underlie the stability characteristics of bimanual coordination but have never been evaluated in conjunction: integrated timing of feedforward control signals, phase entrainment by contralateral afference, and timing corrections based on the perceived error of relative phase. In this study, the relative contributions of these interactions were discerned through systematic comparisons of five tasks involving rhythmic flexion-extension movements about the wrist, performed bimanually (in-phase and antiphase coordination) or unimanually with or without comparable passive movements of the contralateral hand. The main findings were the following. 1) Contralateral passive movements during unimanual active movements induced phase entrainment to interlimb phasing of either 0 degrees (in-phase) or 180 degrees (antiphase). 2) Entrainment strength increased with the passive movements' amplitude, but was similar for in-phase and antiphase movements. 3) Coordination of unimanual active movements with passive movements of the contralateral hand (kinesthetic tracking) was characterized by similar bilateral EMG activity as observed in active bimanual coordination. 4) During kinesthetic tracking the timing of the movements of the active hand was modulated by afference-based error corrections, which were more pronounced during in-phase coordination. 5) Indications of in-phase coordination being more stable than antiphase coordination were most prominent during active bimanual coordination and marginal during kinesthetic tracking. Together the results indicated that phase entrainment by contralateral afference contributed equally to the stability of in-phase and antiphase coordination, and that differential stability of these patterns depended predominantly on integrated timing of feedforward signals, with only a minor role for afference-based error corrections.

Adolescent↗

PubMed2005

Mirrored EMG activity during unimanual rhythmic movements.

We studied instances of mirror movements--in the form of coherent EMG activity of the muscles in the arm not intended to move--during the performance of a unimanual rhythmic task in healthy adults. Epochs of involuntary muscle activity were detected and analyzed using time-resolved spectral methods. The observed frequency and phase locking between EMG patterns derived from homologous extensor muscles indicated the presence of neural cross-talk, which is relevant to the study of interlimb coordination.

Adolescent↗

PubMed2005

Effects of chronic low back pain on trunk coordination and back muscle activity during walking: changes in motor control.

Low back pain (LBP) is often accompanied by changes in gait, such as a decreased (preferred) walking velocity. Previous studies have shown that LBP diminishes the normal velocity-induced transverse counter-rotation between thorax and pelvis, and that it globally affects mean erector spinae (ES) activity. The exact nature and causation of these effects, however, are not well understood. The aim of the present study was to examine in detail the effect of walking velocity on global trunk coordination and ES activity as well as their variability to gain further insights into the effects of non-specific LBP on gait. The study included 19 individuals with non-specific LBP and 14 healthy controls. Gait kinematics and ES activity were recorded during treadmill walking at (1) a self-selected (comfortable) velocity, and (2) sequentially increased velocities from 1.4 up to maximally 7.0 km/h. Pain intensity, fear of movement and disability were measured before the experiment. The angular movements of thorax, lumbar and pelvis were recorded in three dimensions. ES activity was recorded with pairs of surface electrodes. Trunk-pelvis coordination and mean amplitude of ES activity were analyzed. In addition, invariant and variant properties of trunk kinematics and ES activity were studied using principal component analysis (PCA). Comfortable walking velocity was significantly lower in the LBP participants. In the transverse plane, the normal velocity-induced change in pelvis-thorax coordination from more in-phase to more antiphase was diminished in the LBP participants, while lumbar and pelvis rotations were more in-phase compared to the control group. In the frontal plane, intersegmental timing was more variable in the LBP than in the control participants, with additional irregular movements of the thorax. Rotational amplitudes were not significantly different between the LBP and control participants. In the LBP participants, the pattern of ES activity was affected in terms of increased (residual) variability, timing deficits, amplitude modifications and frequency changes. The gait of the LBP participants was characterized by a more rigid and less variable kinematic coordination in the transverse plane, and a less tight and more variable coordination in the frontal plane, accompanied by poorly coordinated activity of the lumbar ES. Pain intensity, fear of movement and disability were all unrelated to the observed changes in coordination, suggesting that the observed changes in trunk coordination and ES activity were a direct consequence of LBP per se. Clinically, the results imply that conservative therapy should consider gait training as well as exercises aimed at improving both intersegmental and muscle coordination.

Adult↗

PubMed2005

Stabilization of bimanual coordination due to active interhemispheric inhibition: a dynamical account.

Based on recent brain-imaging data and congruent theoretical insights, a dynamical model is derived to account for the patterns of brain activity observed during stable performance of bimanual multifrequency patterns, as well as during behavioral instabilities in the form of phase transitions between such patterns. The model incorporates four dynamical processes, defined over both motor and premotor cortices, which are coupled through inhibitory and excitatory inter- and intrahemispheric connections. In particular, the model underscores the crucial role of interhemispheric inhibition in reducing the interference between disparate frequencies during stable performance, as well as the failure of this reduction during behavioral transitions. As an aside, the model also accounts for in- and antiphase preferences during isofrequency movements. The viability of the proposed model is illustrated by magnetoencephalographic signals that were recorded from an experienced subject performing a polyrhythmic tapping task that was designed to induce transitions between multifrequency patterns. Consistent with the models dynamics, contra- and ipsilateral cortical areas of activation were frequency- and phase-locked, while their activation strength changed markedly in the vicinity of transitions in coordination.

Brain Mapping↗

PubMed2005

Visual perception and gaze control in judging versus producing phase relations.

We studied visual perception and gaze control in nine participants while they judged the relative phase between two oscillating stimuli (Experiment 1), and while they moved their hand--and therewith a concurrent feedback signal--in-phase or in antiphase with an oscillating stimulus (Experiment 2). As in previous studies, the mean relative phase judgements in Experiment 1 corresponded to the presented phase relations (0 degree, 45 degrees, 90 degrees, 135 degrees, and 180 degrees), whereas their standard deviations followed an inverted U-function of relative phase. The relative phase judgements were hardly affected by the degree of visibility (fully visible, inner parts occluded, outer parts occluded) and the amplitude (5 degrees, 10 degrees, and 20 degrees) of the stimuli. Stimulus-gaze coupling decreased as relative phase increased, and its variability correlated with that of the relative phase judgements. Taken together, task performance and gaze behaviour suggested that the judgement of relative phase might be flexibly based on different variables, rather than a single variable like relative direction of motion. In Experiment 2, the production of the antiphase relation was less stable than that of the in-phase relation. Performance deteriorated when the outer parts of the signals were occluded and when their amplitudes were reduced. Stimulus-gaze coupling was stronger during in-phase than during antiphase tracking and weaker when the signals were partially occluded and when their amplitudes were reduced. Stimulus-gaze coupling at 0 degrees and 180 degrees was stronger in Experiment 2 than in Experiment 1, suggesting that the visual perception of relative phase may benefit from its active production. Overall, the results clearly indicated that visual perception of relative phase and the corresponding gaze control are strongly task-dependent.

Adult↗

PubMed2005

How position, velocity, and temporal information combine in the prospective control of catching: data and model.

The cerebral cortex contains circuitry for continuously computing properties of the environment and one's body, as well as relations among those properties. The success of complex perceptuomotor performances requires integrated, simultaneous use of such relational information. Ball catching is a good example as it involves reaching and grasping of visually pursued objects that move relative to the catcher. Although integrated neural control of catching has received sparse attention in the neuroscience literature, behavioral observations have led to the identification of control principles that may be embodied in the involved neural circuits. Here, we report a catching experiment that refines those principles via a novel manipulation. Visual field motion was used to perturb velocity information about balls traveling on various trajectories relative to a seated catcher, with various initial hand positions. The experiment produced evidence for a continuous, prospective catching strategy, in which hand movements are planned based on gaze-centered ball velocity and ball position information. Such a strategy was implemented in a new neural model, which suggests how position, velocity, and temporal information streams combine to shape catching movements. The model accurately reproduces the main and interaction effects found in the behavioral experiment and provides an interpretation of recently observed target motion-related activity in the motor cortex during interceptive reaching by monkeys. It functionally interprets a broad range of neurobiological and behavioral data, and thus contributes to a unified theory of the neural control of reaching to stationary and moving targets.

Adult↗