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.     

The role of movement speed in learning a visuo-manual coordination in children

Summary The aim of the present study was to investigate the processes underlying aiming movements (motor programming and feedback control), and to explore their modification through learning. Two groups of 6- and 9-year-old children were asked to perform a directional aiming task without visual feedback (open-loop situation). After 15 trials (pretest) all subjects were submitted to a practice session which consisted of three series of trials with visual feedback (closed-loop situation). Half of the subjects had to perform the task at maximum speed (programmed movements), while the other half was required to perform slow movements (feedback-controlled movements). After the practice session all subjects were tested again in the openloop situation without time constraints (posttest). The results showed that during the practice session, accuracy was greater than in the two test conditions. It was greater in the case of slow movements than in the case of rapid ones. Moreover, in the case of rapid movements, it did not improve over the three practice series, while it did improve with slow movements. The difference between pre- and posttests showed that both groups improved their accuracy with practice in all conditions, the greatest improvement being obtained with rapid practice movements in 9-year-old children. It is suggested that different types of feedback (on-line and delayed feedback) contribute in varying degrees to the improvement of the aiming movements. However, the rapid movement condition, which requires a greater efficiency of programming, was found to be more effective for learning than the slow movement condition. The age-related differences found in learning suggest that feedback information can be fully integrated into motor programming only after 6 years of age.     

An interpretation of research of feedback interruption in speech.

The controversial question of the scope of sensory control in the voluntary motor patterns involved in speech is examined by reviewing studies in which the auditory, tactile, and proprioceptive feedback channels have been distorted or interrupted. The author makes a case for open loop control of well-learned speech patterns under normal circumstances. The concept of internal feedback is introduced as a possible control system of skilled speech, whereas response feedback and external feedback are viewed as necessary for children developing speech or adults learning new speech patterns.     

An interpretation of research on feedback interruption in speech

The controversial question of the scope of sensory control in the voluntary motor patterns involved in speech is examined by reviewing studies in which the auditory, tactile, and proprioceptive feedback channels have been distorted or interrupted. The author makes a case for open loop control of well-learned speech patterns under normal circumstances. The concept of internal feedback is introduced as a possible control system of skilled speech, whereas response feedback and external feedback are viewed as necessary for children developing speech or adults learning new speech patterns.     

Role of the striatum and the cerebellum in motor skill acquisition

Motor skill acquisition was investigated in patients with Parkinson's disease (PD) or cerebellar dysfunction using two sensory-guided tracking tasks. The subjects had to learn to track a visual target (a square) on a computer screen by moving a joystick under two different conditions. In the unreversed task, the horizontal target movements were semi-predictable and could be anticipated. In the reversed task, the horizontal movements of a pointer which had to be kept within the target square were mirror-reversed to the joystick movements. PD patients showed intact learning of the semi-predictable task and reduced learning of the mirror-reversed task; patients with cerebellar dysfunction showed the opposite pattern. These findings are discussed in relation to the differential contribution of the cerebellum and the striatum to motor skill acquisition: the cerebellum appears to participate in the implementation of anticipatory movements, whereas the striatum may be critically involved in types of motor learning which require a high degree of internal elaboration.     

Role of the striatum and the cerebellum in motor skill acquisition

Motor skill acquisition was investigated in patients with Parkinson's disease (PD) or cerebellar dysfunction using two sensory-guided tracking tasks. The subjects had to learn to track a visual target (a square) on a computer screen by moving a joystick under two different conditions. In the unreversed task, the horizontal target movements were semi-predictable and could be anticipated. In the reversed task, the horizontal movements of a pointer which had to be kept within the target square were mirror-reversed to the joystick movements. PD patients showed intact learning of the semi-predictable task and reduced learning of the mirror-reversed task; patients with cerebellar dysfunction showed the opposite pattern. These findings are discussed in relation to the differential contribution of the cerebellum and the striatum to motor skill acquisition: the cerebellum appears to participate in the implementation of anticipatory movements, whereas the striatum may be critically involved in types of motor learning which require a high degree of internal elaboration.     

Visuomotor Adaptation and Proprioceptive Recalibration

ABSTRACT

Motor learning, in particular motor adaptation, is driven by information from multiple senses. For example, when arm control is faulty, vision, touch, and proprioception can all report on the arm's movements and help guide the adjustments necessary for correcting motor error. In recent years we have learned a lot about how the brain integrates information from multiple senses for the purpose of perception. However, less is known about how multisensory data guide motor learning. Most models of, and studies on, motor learning focus almost exclusively on the ensuing changes in motor performance without exploring the implications on sensory plasticity. Nor do they consider how discrepancies in sensory information (e.g., vision and proprioception) related to hand position may affect motor learning. Here, we discuss research from our lab and others that shows how motor learning paradigms affect proprioceptive estimates of hand position, and how even the mere discrepancy between visual and proprioceptive feedback can affect learning and plasticity. Our results suggest that sensorimotor learning mechanisms do not exclusively rely on motor plasticity and motor memory, and that sensory plasticity, in particular proprioceptive recalibration, plays a unique and important role in motor learning.     

Vision,proprioception and corollary discharge in a movement recall test

Movement recall was investigated in relation to the sensory processes involved in a triangle drawing task.Forty subjects in two groups, one with and one without visual feedback, performed a recall task involving movements of their index finger. All subjects attended different experimental sessions in which (1) all proprioceptive feedback was eliminated by the ischaemic block technique, (2) muscle spindle feedback was distorted by vibration of the muscles and tendons involved in the movement, and (3) proprioceptive feedback was normal.Within each session subjects were required firstly to recall triangular movements made for them passively by the experimenter, and secondly, to recall movements they had made actively. Results indicated comparable accuracy in recall of active movements in all conditions, and a decrement in passive recall dependent on the availability of the alternative sources of feedback. The results indicated a process of integrated contribution of all inputs to the perception of movement; redundancy in information when all channels are available; and a role of corollary discharge in recall of movements.     

Interactions Between Tactile and Proprioceptive Representations in Haptics

ABSTRACT

Neuroprosthetic limbs, regardless of their sophisticated motor control, require sensory feedback to viably interact with the environment. Toward that aim, the authors examined interrelationships between tactile and proprioceptive sensations. Through human psychophysics experiments, they evaluated error patterns of subjects estimating hand location in a horizontal 2-dimensional workspace under 3 tactile conditions. While tactile cues did not significantly affect the structure of the pattern of errors, touching the workspace reduced estimation errors. During neurophysiological experiments, a macaque grasped textured objects using 2 hand postures. Sensory coding showed dependence on both roughness of the manipulandum and posture. In summary, the authors suggest that tactile sensations underlying haptics are processed in a stable spatial reference frame provided by a proprioceptive system, and that tactile and proprioceptive inputs can be encoded simultaneously by individual cells. Such insights will be useful for providing stable, adaptive sensory feedback for neuroprosthetics.     

Feedback and intention during motor-skill learning: a connection with prospective memory

The intention to complete an action in the future can improve the learning of this action, but it is unknown whether this effect persists when feedback is manipulated during encoding. In Experiment 1, participants were instructed to learn a motor skill with or without intending to reproduce this learning in the future, and feedback on their movements was administrated by self-decision, that is, participants asked for feedback whenever they wanted it. The results showed that intention increased the frequency with which feedback was requested, but did not improve motor performance. In Experiment 2, participants had to learn the task with high or few feedbacks, which they could not control. In these conditions, intention was beneficial in promoting motor learning only for a low feedback schedule. We suggest that the beneficial effect of intention on learning can be overshadowed or emphasised by the feedback processing during encoding. These findings are discussed in light of theories surrounding prospective memory.     

Aging affects motor learning but not savings at transfer of learning

Two important components of skill learning are the learning process itself (motor acquisition) and the ability to transfer what has been learned to new task variants (motor transfer). Many studies have documented age-related declines in the ability to learn new manual motor skills. In this study, I tested whether the degree of savings at transfer of learning is similarly affected by advancing age. Young and older adults made aiming movements with a joystick to hit targets presented on a computer screen, with real-time feedback display of their movement. They adapted to three different rotations of the feedback display in a sequential fashion, with return to the normal feedback display between each. Adaptation performance was better when it was preceded by other adaptive experiences, regardless of age.     

Deficit in learning of a motor skill requiring strategy, but not of perceptuomotor recalibration, with aging

We investigated the effect of aging on different aspects of motor skill learning using two computer-presented perceptuomotor tasks. The relationship between visual and proprioceptive feedback was transformed in the first task, which was open to the formation and use of strategies. This task was designed to lead to perceptuomotor adaptation that was then measured by performance on a very similar second task that was not open to the use of strategy task. Older participants showed impaired learning of the strategic task but not of the nonstrategic task. This is in line with the suggestion that the effect of aging on learning and memory may be to reduce working memory resources.     

Augmented Feedback Presented in a Virtual Environment Accelerates Learning of a Difficult Motor Task

One can use a number of techniques (e.g., from videotaping to computer enhancement of the environment) to augment the feedback that a subject usually receives during training on a motor task. Although some forms of augmented feedback have been shown to enhance performance on isolated isometric tasks during training, when the feedback has been removed subjects have sometimes not been able to perform as well in the "real-world" task as controls. Indeed, for realistic, nonisometric motor tasks, improved skill acquisition because of augmented feedback has not been demonstrated. In the present experiments, subjects (Experiment 1, N = 42; Experiment 2, N = 21) performed with a system that was designed for teaching a difficult multijoint movement in a table tennis environment. The system was a fairly realistic computer animation of the environment and included paddles for the teacher and subject, as well as a virtual ball. Each subject attempted to learn a difficult shot by matching the pattern of movements of the expert teacher. Augmented feedback focused the attention of the subject on a minimum set of movement details that were most relevant to the task; feedback was presented in a form that required the least perceptual processing. Effectiveness of training was determined by measuring their performance in the real task. Subjects who received the virtual environment training performed significantly better than subjects who received a comparable amount of real-task practice or coaching. Kinematic analysis indicated that practice with the expert's trajectory served as a basis for performance on the real-world task and that the movements executed after training were subject-specific modifications of the expert's trajectory. Practice with this trajectory alone was not sufficient for transfer to the real task, however: When a critical component of the virtual environment was removed, subjects showed no transfer to the real task.     

Larger plantar flexion torque variability implies less stable balance in the young: An association affected by knee position

The present study examined the association between plantar flexion torque variability during isolated isometric contractions and during quiet bipedal standing. For plantar flexion torque measurements in quiet stance (QS), subjects stood still over a force plate. The mean plantar flexion torque level exerted by each subject in QS (divided by 2 to give the torque due to a single leg) served as the target torque level for right leg force-matching tasks in extended knee (KE) and flexed knee (KF) conditions. Muscle activation levels (EMG amplitudes) of the triceps surae and mean, standard deviation and coefficient of variation of plantar flexion torque were computed from signals acquired during periods with and without visual feedback. No significant correlations were found between EMG amplitudes and torque variability, regardless of the condition and muscle being analyzed. A significant correlation was found between torque variability in QS and KE, whereas no significant correlation was found between torque variability in QS and KF, regardless of vision availability. Therefore, torque variability measured in a controlled extended knee plantar flexion contraction is a predictor of torque variability in the anterior-posterior direction when the subjects are in quiet standing. In other words, larger plantar flexion torque variability in KE (but not in KF) implies less stable balance. The mechanisms underlying the findings above are probably associated with the similar proprioceptive feedback from the triceps surae in QS and KE and poorer proprioceptive feedback from the triceps surae in KF due to the slackening of the gastrocnemii. An additional putative mechanism includes the different torque contributions of each component of the triceps surae in the two knee angles. From a clinical and research standpoint, it would be advantageous to be able to estimate changes in balance ability by means of simple measurements of torque variability in a force matching task.     

Perceptual skills of children with developmental coordination disorder

The aim of this study was to investigate whether children with a Developmental Coordination Disorder (DCD) experience problems in the processing of visual, proprioceptive or tactile information. Different aspects of visual perception were tested with the Developmental Test of Visual Perception (DTVP-2), tactile perception was assessed with the Tactual Performance Test (TPT), and a manual pointing task was employed to measure the ability to use visual and proprioceptive information in goal-directed movements. Nineteen children with DCD and nineteen age and sex-matched controls participated in this study. Differences between groups were most pronounced in the subtests measuring visual-motor integration of the DTVP-2, and in two subtests measuring visual perception (visual closure and position in space). On average the children with DCD performed slightly below the norm for tactile perception, with only three children failing the norm. On the manual pointing task, children with DCD made inconsistent responses towards the targets in all three conditions (visual, visual-proprioceptive and proprioceptive condition). No significant differences between groups were found for absolute error. Inspection of the individual data revealed that only two children failed on the majority of perceptual tasks in the three modalities. Across tasks, no consistent pattern of deficits appeared, illustrating the heterogeneity of the problems of children with DCD.     

An examination of methods for producing relaxation during short-term laboratory sessions

Reductions in psychological and physiological correlates of tension produced by various muscle relaxation training techniques were examined during a short-term laboratory session. Two studies are described involving a combined total of one hundred subjects receiving either abbreviated progressive relaxation, visual, auditory, or tactile electromyographic (EMG) biofeedback procedures. The Anxiety Differential was administered before and after the laboratory session. Heart rate, respiratory rate, skin conductance, systolic blood pressure, and frontalis and dominant forearm extensor EMG measures were obtained before, during, and after administration of relaxation training. Results indicated feedback in the tactile modality to produce overall reductions in tension comparable to those produced by progressive relaxation. Overall reductions in tension displayed by both progressive relaxation and tactile feedback were generally greater than reductions shown by visual or auditory feedback procedures. Interpretations suggest that certain forms of EMG feedback may offer an alternative to progressive relaxation techniques for producing short-term reductions in tension. Feedback modality is further indicated as a potentially important variable during relaxation training using the EMG feedback technique.     

Deficits of anticipatory grip force control after damage to peripheral and central sensorimotor systems

Healthy subjects adjust their grip force economically to the weight of a hand-held object. In addition, inertial loads, which arise from arm movements with the grasped object, are anticipated by parallel grip force modulations. Internal forward models have been proposed to predict the consequences of voluntary movements. Anesthesia of the fingers impairs grip force economy but the feedforward character of the grip force/load coupling is preserved. To further analyze the role of sensory input for internal forward models and to characterize the consequences of central nervous system damage for anticipatory grip force control, we measured grip force behavior in neurological patients. We tested a group of stroke patients with varying degrees of impaired fine motor control and sensory loss, a single patient with complete and permanent differentation from all tactile and proprioceptive input, and a group of patients with amyotrophic lateral sclerosis (ALS) that exclusively impairs the motor system without affecting sensory modalities. Increased grip forces were a common finding in all patients. Sensory deficits were a strong but not the only predictor of impaired grip force economy. The feedforward mode of grip force control was typically preserved in the stroke patients despite their central sensory deficits, but was severely disturbed in the patient with peripheral sensory deafferentation and in a minority of stroke patients. Moderate deficits of feedforward control were also obvious in ALS patients. Thus, the function of the internal forward model and the precision of grip force production may depend on a complex anatomical and functional network of sensory and motor structures and their interaction in time and space.     

Adults with probable developmental coordination disorder selectively process early visual,but not tactile information during action preparation. An electrophysiological study

Developmental coordination disorder (DCD) is a neurodevelopmental condition affecting motor coordination in children and adults. Here, EEG signals elicited by visual and tactile stimuli were recorded while adult participants with and without probable DCD (pDCD) performed a motor task. The task cued reaching movements towards a location in visible peripersonal space as well as an area of unseen personal space. Event-related potentials elicited by visual and tactile stimuli revealed that visual processing was strongly affected by movement preparation in the pDCD group, even more than in controls. However, in contrast to the controls, tactile processing in unseen space was unaffected by movement preparation in the pDCD group. The selective use of sensory information from vision and proprioception is fundamental for the adaptive control of movements, and these findings suggest that this is impaired in DCD. Additionally, the pDCD group showed attenuated motor rhythms (beta: 13–30 Hz) over sensorimotor regions following cues to prepare movements towards unseen personal space. The results reveal that individuals with pDCD exhibit differences in the neural mechanisms of spatial selection and action preparation compared to controls, which may underpin the sustained difficulties they experience. These findings provide new insights into the neural mechanisms potentially disrupted in this highly prevalent disorder.     

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.     

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5–30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P < .05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P < .05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P < .05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.