Sensory feedback in the learning of a novel motor task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement an provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than "natural" (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

Sensory Feedback in the Learning of a Novel Motor Task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement can provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than “natural” (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

Value of mechanographic studies in neuromuscular function diagnosis

Mechanographic examinations have hitherto played only a minor role in general clinical neuromuscular functional diagnostics. The purpose of this contribution is, therefore, to present an appropriate recording apparatus (W. Zett , 1969), to report on the values that can be considered normal and to outline the diagnostic value of the method using clinical applications as examples. Special value is attached to simultaneous recording of the EMG and the mechanograph because this method permits differentiated conclusions to be drawn regarding disturbances in muscular activity, the electromechanical coupling and the actual process of contraction. The method is also important for pharmacological investigations and should be used principally in connection with musclepathology for objectifying the effects of medication.     

Age-related EMG variables during maximum voluntary contraction

We studied the neuromuscular adaptation that occurs with aging by comparing changes in surface electromyography (EMG) variables from the tibialis anterior muscle in 12 young (21.4 +/- 1.7 yr. old) and 13 older subjects (70.8 +/- 3.1 yr. old). EMG variables such as the muscle fiber conduction velocity, median frequency, and averaged rectified value were calculated during maximum voluntary contraction for 5-sec. isometric contractions. The dorsiflexion force, muscle fiber conduction velocity, median frequency, and average rectified value during maximum voluntary contraction were significantly smaller in the older than in the younger group (p < .05). These results suggested that the neuromuscular system in older subjects is affected by the selective atrophy of fast twitch fibers and differences in motor unit firing statistics. Our results suggest the utility of applying the EMG observed during maximum voluntary contraction to the noninvasive evaluation of neuromuscular function in elderly persons.     

Time-dependence between upper arm muscles activity during rapid movements: Observation of the proportional effects predicted by the kinematic theory

Rapid human movements can be assimilated to the output of a neuromuscular system with an impulse response modeled by a Delta-Lognormal equation. In such a model, the main assumption concerns the cumulative time delays of the response as it propagates toward the effector following a command. To verify the validity of this assumption, delays between bursts in electromyographic (EMG) signals of agonist and antagonist muscles activated during a rapid hand movement were investigated. Delays were measured between the surface EMG signals of six muscles of the upper limb during single rapid handwriting strokes. From EMG envelopes, regressions were obtained between the timing of the burst of activity produced by each monitored muscle. High correlation coefficients were obtained supporting the proportionality of the cumulative time delays, the basic hypothesis of the Delta-Lognormal model. A paradigm governing the sequence of muscle activities in a rapid movement could, in the long run, be useful for applications dealing with the analysis and synthesis of human movements.     

An Examination of Rapid Positioning Movements with Spatiotemporal Constraints

Unidirectional positioning movements with spatiotemporal-constraints were examined as a test of impulse-timing theory (Schmidt, 1976; 1980; Wallace, 1981). Movements were examined at the kinematic, kinetic, and neuromuscular levels in three experiments. In the first experiment, displacement was held constant while five different movement times were examined. Both amplitudes and durations of the EMG and the kinetic variables were related to movement time. The results generally support the impulse-timing model. In the second experiment, movements were performed to a target at each of four distances in a constant movement time. EMG and force amplitudes and, unexpectedly, accelerative-force duration were modulated to achieve changes in displacement when movement time was constant. In the third experiment, movement time and displacement were simultaneously varied resulting in four conditions with equal average velocities. The results of this experiment were not as clear and exhibited individual differences. EMG duration did not always vary with changes in movement time. The results of all three experiments could not be adequately accounted for by the impulse-timing model.     

An examination of rapid positioning movements with spatiotemporal constraints

Unidirectional positioning movements with spatiotemporal constraints were examined as a test of impulse-timing theory (Schmidt, 1976; 1980; Wallace, 1981). Movements were examined at the kinematic, kinetic, and neuromuscular levels in three experiments. In the first experiment, displacement was held constant while five different movement times were examined. Both amplitudes and durations of the EMG and the kinetic variables were related to movement time. The results generally support the impulse-timing model. In the second experiment, movements were performed to a target at each of four distances in a constant movement time. EMG and force amplitudes and, unexpectedly, accelerative-force duration were modulated to achieve changes in displacement when movement time was constant. In the third experiment, movement time and displacement were simultaneously varied resulting in four conditions with equal average velocities. The results of this experiment were not as clear and exhibited individual differences. EMG duration did not always vary with changes in movement time. The results of all three experiments could not be adequately accounted for by the impulse-timing model.     

An equilibrium-point model for fast, single-joint movement: I. Emergence of strategy-dependent EMG patterns

We describe a model for the regulation of fast, single-joint movements, based on the equilibrium-point hypothesis. Limb movement follows constant rate shifts of independently regulated neuromuscular variables. The independently regulated variables are tentatively identified as thresholds of a length sensitive reflex for each of the participating muscles. We use the model to predict EMG patterns associated with changes in the conditions of movement execution, specifically, changes in movement times, velocities, amplitudes, and moments of limb inertia. The approach provides a theoretical neural framework for the dual-strategy hypothesis, which considers certain movements to be results of one of two basic, speed-sensitive or speed-insensitive strategies. This model is advanced as an alternative to pattern-imposing models based on explicit regulation of timing and amplitudes of signals that are explicitly manifest in the EMG patterns.     

The effect of force-controlled biting on human posture control

Several studies have confirmed the neuromuscular effects of jaw motor activity on the postural stability of humans, but the mechanisms of functional coupling of the craniomandibular system (CMS) with human posture are not yet fully understood. The purpose of our study was, therefore, to investigate whether submaximum biting affects the kinematics of the ankle, knee, and hip joints and the electromyographic (EMG) activity of the leg muscles during bipedal narrow stance and single-leg stance. Twelve healthy young subjects performed force-controlled biting (FB) and non-biting (NB) during bipedal narrow stance and single-leg stance. To investigate the effects of FB on the angles of the hip, knee, and ankle joints, a 3D motion-capture system (Vicon MX) was used. EMG activity was recorded to enable analysis of the coefficient of variation of the muscle co-contraction ratios (CVR) of six pairs of postural muscles. Between FB and NB, no significant differences were found for the mean values of the angles of the ankle, knee, and hip joints, but the standard deviations were significantly reduced during FB. The values of the ranges of motion and the mean angular velocities for the three joints studied revealed significant reduction during FB also. CVR was also significantly reduced during FB for five of the six muscle pairs studied. Although submaximum biting does not change the basic strategy of posture control, it affects neuromuscular co-contraction patterns, resulting in increased kinematic precision.     

What happens between an external stimulus and an overt response?

Peripheral components of feedthrough loops were psychophysiologically measured from the brain, both forelimbs, the tongue and the eyes during simple and choice reaction time tasks using linguistic and non-linguistic stimuli. Closing a microswitch with the little finger was the overt response. Covert electromyographic (EMG) responses were computer identified in the following average temporal order: generally, the earliest covert reactions were in the tongue, brain, eyes, and passive arm-hand region. Next were complex EMG events in the active limb. These covert reactions may function in feedthrough loops to generate and transmit codes during internal information processing. The passive armhand responses occurred significantly earlier than the onset of the covert EMG burst for closing the microswitch; perhaps there is an inhibitory response “commanding” the passive arm not to respond, before the other (active) limb can overtly respond. Mean response patterns to linguistic and non-linguistic stimuli were almost identical. Reaction time to the onset of the EMG burst for switch closing was from 40 to 95 milliseconds earlier than the usual overt reaction time measure (that to switch closing), suggesting that reaction time studies might be improved by using the onset of EMG increase as the more sensitive and precise measure.     

The effects of success and failure on the patterning of neuromuscular energy

Weinberg and Hunt (1976) demonstrated that high- and low-anxious subjects differed in their patterning of neuromuscular energy in performance under failure feedback. The present study extends these findings to conditions that involve success feedback. The Sport Competition Anxiety Test and State-Trait Anxiety Inventory were administered to distinguish A-State and A-Trait subjects, while EMG indicated qualitative aspects of throwing. High-and low-trait anxiety subjects received either success, failure, or no feedback. High-anxious subjects performed best under success feedback, and low-anxious subjects performed best after failure feedback. High-anxious subjects used more EMG energy before, during, and after the throw in all conditions, and success feedback was beneficial for high-anxious subjects. The results are discussed in terms of the inter-relationships between efficiency of neuromuscular energy, motor performance, and state anxiety.     

Initiation of Bilateral Responses in a Kinesthetic Reaction Time Task

Two experiments are presented in which different mechanisms controlling each limb in a bilateral arm response to a unilateral kinesthetic stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus limb was described as operating with relative invariance by using a tightly coupled input-output reflexive pathway, whereas the nonstimulus limb appeared to be controlled by higher-order processing thought to be more susceptible to influences such as hemispheric specialization and stimulus expectancy. The differential control model was further tested in Experiment 2 by retaining the intrahemispheric pathway of the unilateral kinesthetic stimulus but experimentally uncoupling the reflex mechanism from the stimulus side. Analyses of bilateral EMG premotor latencies under these conditions revealed that each response side can be controlled at separate levels —i.e., by a reflexive type mechanism or by higher-order processing when one of the response limbs is also the stimulus limb. When the stimulus is on the same side but not generated by either responding limb, both sides reflect behavior that is best described by an information processing type of voluntary control.     

Initiation of bilateral responses in a kinesthetic reaction time task

Two experiments are presented in which different mechanisms controlling each limb in a bilateral arm response to a unilateral kinesthetic stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus are postulated to occur. In Experiment 1, the limb serving as the stimulus limb was described as operating with relative invariance by using a tightly coupled input-output reflexive pathway, whereas the nonstimulus limb appeared to be controlled by higher-order processing thought to be more susceptible to influences such as hemispheric specialization and stimulus expectancy. The differential control model was further tested in Experiment 2 by retaining the interhemispheric pathway of the unilateral kinesthetic stimulus but experimentally uncoupling the reflex mechanism from the stimulus side. Analyses of bilateral EMG premotor latencies under these conditions revealed that each response side can be controlled at separate levels-i.e., by a reflexive type mechanism or by higher-order processing when one of the response limbs is also the stimulus limb, both sides reflect behavior that is best described by an information processing type of voluntary control.     

Delayed sensory feedback in the learning of a novel motor task

Summary Generally the therapeutical effect of EMG feedback is viewed in terms of the immediate contiguity between response and information. According to this view any feedback delay would deteriorate the result. In this article the validity of this notion has been investigated. Three groups of normal subjects were required to perform a difficult movement under three feedback conditions: immediate EMG feedback, delayed EMG feedback, and a control (no EMG feedback) condition. The results indicated a significant difference between the EMG feedback groups and the control condition. However, no such difference was found between the immediate and delayed feedback conditions. The results suggested that the immediacy of the feedback is not the main factor in EMG feedback, but the specificity of the information.This study was supported by Grant no. 15-35-03 from the Netherlands Organization for the Advancement of Pure Research     

Automatic behavioural responses to valence: Evidence that facial action is facilitated by evaluative processing

Are motor schemata of facial action spontaneously activated upon the processing of evaluative information? In this case, the processing of positive evaluative information should immediately trigger the motor schema of smiling, and the processing of negative information should trigger frowning. This hypothesis was tested in two experiments in which participants were required to respond to positive and negative words by either smiling or frowning. Electromyogram (EMG) activity was recorded over the brow muscle region (corrugator supercilii) and over the cheek muscle region (zygomaticus major) in order to quantify the latency of muscular response as a dependent measure. In Experiment 1 we found that participants were faster at contracting their zygomaticus muscle (which is involved in smiling) when evaluating positive words, and faster at contracting their corrugator muscle (which is involved in frowning) when evaluating negative words. In Experiment 2, participants were required to respond with the contraction of one of the two muscles whenever a word appeared on the computer screen. Again, we found that responses were faster to congruent response valence combinations than to incongruent response valence combinations. These findings support the hypothesis that evaluative processing is directly linked to motor schemata of facial muscles.     

A comparison of EMG and SCL in normal and depressed subjects

Skin conductance level (SCL) and electromyograms (EMGs) recorded from three muscle sites were compared for 15 female hospitalized psychiatric patients meeting diagnostic criteria for primary affective disorder and 15 age- and race-matched controls. The depressed subjects had significantly lower SCL and significantly higher resting EMG levels recorded from one muscle site. Electromyogram and SCL were not found to be significantly correlated with each other or with measures of anxiety or depression for the patients with primary affective disorder. Normal controls, however, showed significant correlations between a measure of depression and both EMG and SCL. These results are discussed with suggestions for future research.     

Speed-accuracy trade-offs in myocontrol

Myoelectric (EMG) signals are used in assistive technology for prostheses, computer and domestic control. However, little is known about the capacity of controlling these signals. Specifically, it is unclear whether myocontrol, i.e., the control of myoelectric signals, obeys the same laws as motor control. Neurologically intact adult participants performed pointing tasks with EMG signals captured from the forehead or the hand in two modalities (sustained: stabilize the signal amplitude in the target; impulsion: produce an impulse and return to resting level). In the sustained modality, the time to reach the target (reach time) increased logarithmically with target amplitude, which is compatible with the predictions of Fitts' law. The rate of failure was not significantly affected by target amplitude. In the impulsion modality, the reach time and the rate of failure followed a bow-shaped pattern as a function of target amplitude. Stabilization time in the sustained modality followed a convex (bow-shaped) pattern for the forehead and a concave pattern for the hand. This was the only significant effect of electrode placement in this study. These findings suggest that myocontrol obeys laws that are distinct from those determining motor control, and that the muscular and intra-muscular synergies that produce EMG signals are specific of each pointing modality and target amplitude.     

Influence of mental practice on development of voluntary control of a novel motor acquisition task

The purpose of this investigation was to assess whether mental practice facilitates the development of voluntary control over the recruitment of the abductor hallucis muscle to produce isolated big toe abduction. A sample of convenience of 15 women and 20 men with a mean age of 28.8 yr. (SD=5.7) and healthy feet, who were unable voluntarily to abduct the big toe, were randomly assigned to one of three groups, a mental practice group, a physical practice group, and a group who performed a control movement during practice. Each subject received neuromuscular electrical stimulation to introduce the desired movement prior to each of five practice bouts over a single session lasting 2 hr. Big toe abduction active range of motion and surface electromyographic (EMG) output of the abductor hallucis and extensor digitorum brevis muscles were measured prior to the first practice bout and following each practice bout, yielding seven acquisition trials. Acquisition is defined as an improvement in both active range of motion and in the difference between the integrated EMG of the abductor hallucis and extensor digitorum brevis muscles during successive acquisition trials. Seven members of both the mental and physical practice groups and one member of the control group met the acquisition criteria. Chi-square analysis indicated the group difference was statistically significant, suggesting mental practice was effective for this task.     

Ankle muscles activation and postural stability with Star Excursion Balance Test in healthy individuals

IntroductionThe ankle joint, a part of the kinetic chain of the lower limb, plays a significant role in the maintenance of postural stability during bipedal and unipedal balancing activities. This study aimed to evaluate the neuromuscular control of the ankle joint and the postural stability while executing the Star Excursion Balance Test (SEBT), by recording the EMG activity of the extrinsic ankle musculature and the displacement of the center of pressure (CoP).MethodsThe EMG activity of the tibialis anterior (TA), the peroneus brevis (PB) and the medial and lateral gastrocnemius (GM, GL), along with the anteroposterior and mediolateral displacements (APd and MLd) of CoP as well as the plantar pressure distribution of the supportive lower limb were recorded during reaching to the eight directions of SEBT in 29 healthy, physically active college students (15 males and 14 females; mean ± SD of age 25.6 ± 4.5 yrs.; height: 172.5 ± 8.2 cm; body weight: 67.7 ± 13.6 kg; and BMI: 22.6 ± 2.9 kg/m²).ResultsThe tibialis anterior muscle demonstrated the greatest EMG activity during SEBT, followed by the PB, GL and GM muscles. The increased EMG activity of TA and PB during the execution of all posterior-oriented and lateral directions coincided with a decreased APd of CoP and increased reaching distances. The opposite occurred during the execution of all the anterior-oriented and medial directions. The differences among the directions of SEBT regarding the EMG activity of GL, GM and the mediolateral displacement of CoP were, in general, not significant.ConclusionsThe neuromuscular control of the ankle joint and the associated postural stability during SEBT was highly depended upon the activation level of TA and PB, which should be considered by clinicians and sports specialists when using this test for screening and/or rehabilitation purposes.     

Effects of voluntary activation on neuromuscular endurance analyzed by surface electromyography

The purpose was to examine the relation between voluntary muscle activation and neuromuscular endurance of individual subjects based on the pattern of surface electromyography (EMG). The voluntary muscle activation was estimated from the relation between voluntary force and tetanic force superimposed on the voluntary force (twitch interpolation technique). 14 male subjects (10 regular exercisers and 4 sedentary; 21-29 years old) were divided into a High Voluntary Activation group and a Low Voluntary Activation group. A significant positive correlation of .72 (p<.01) was found between maximum voluntary torque and voluntary activation. A fatigue test was conducted during isometric contractions of 60% and 20% maximum voluntary torque. The endurance time was significantly longer for the Low Voluntary Activation group than the High Voluntary Activation group. The mean power frequency of voluntary EMG obtained from the vastus lateralis muscle decreased consistently whereas the average rectified value increased. The final change of mean power frequency relative to the initial value was significantly greater in the 60% Fatigue task than in the 20% Fatigue task. For the 60% Fatigue task, the final change of mean power frequency and average rectified value relative to the initial value was significantly greater in the Low Voluntary Activation group than in the High Voluntary Activation group. These results suggest that the individual differences in voluntary activation determine the neuromuscular performance usually evaluated as maximum voluntary torque and endurance time and that the voluntary activation may depend on the daily exercise.