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Trunk compensatory movements frequently manifest during robotic-assisted arm reaching exercises for upper limb rehabilitation following a stroke, potentially impeding functional recovery. These aberrant movements are prevalent among stroke survivors and can hinder their progress in rehabilitation, making it crucial to address this issue. This study evaluated the efficacy of visual feedback, facilitated by an RGB-D camera, in reducing trunk compensation. In total, 17 able-bodied individuals and 18 stroke survivors performed reaching tasks under unrestricted trunk conditions and visual feedback conditions. In the visual feedback modalities, the target position was synchronized with trunk movement at ratios where the target moved at the same speed, double, and triple the trunk's motion speed, providing real-time feedback to the participants. Notably, trunk compensatory movements were significantly diminished when the target moved at the same speed and double the trunk's motion speed. Furthermore, these conditions exhibited an increase in the task completion time and perceived exertion among stroke survivors. This outcome suggests that visual feedback effectively heightened the task difficulty, thereby discouraging unnecessary trunk motion. The findings underscore the pivotal role of customized visual feedback in correcting aberrant upper limb movements among stroke survivors, potentially contributing to the advancement of robotic-assisted rehabilitation strategies. These insights advocate for the integration of visual feedback into rehabilitation exercises, highlighting its potential to foster more effective recovery pathways for post-stroke individuals by minimizing undesired compensatory motions. [ABSTRACT FROM AUTHOR]

Robot arm motion control is a fundamental aspect of robot capabilities, with arm reaching ability serving as the foundation for complex arm manipulation tasks. However, traditional inverse kinematics-based methods for robot arm reaching struggle to cope with the increasing complexity and diversity of robot environments, as they heavily rely on the accuracy of physical models. In this paper, we introduce an innovative approach to robot arm motion control, inspired by the cognitive mechanism of inner rehearsal observed in humans. The core concept revolves around the robot's ability to predict or evaluate the outcomes of motion commands before execution. This approach enhances the learning efficiency of models and reduces the mechanical wear on robots caused by excessive physical executions. We conduct experiments using the Baxter robot in simulation and the humanoid robot PKU-HR6.0 II in a real environment to demonstrate the effectiveness and efficiency of our proposed approach for robot arm reaching across different platforms. The internal models converge quickly and the average error distance between the target and the end-effector on the two platforms is reduced by 80% and 38%, respectively. [ABSTRACT FROM AUTHOR]

Noises are ubiquitous in sensorimotor interactions and contaminate the information provided to the central nervous system (CNS) for motor learning. An interesting question is how the CNS manages motor learning with imprecise information. Integrating ideas from reinforcement learning and adaptive optimal control, this paper develops a novel computational mechanism to explain the robustness of human motor learning to the imprecise information, caused by control-dependent noise that exists inherently in the sensorimotor systems. Starting from an initial admissible control policy, in each learning trial the mechanism collects and uses the noisy sensory data (caused by the control-dependent noise) to form an imprecise evaluation of the performance of the current policy and then constructs an updated policy based on the imprecise evaluation. As the number of learning trials increases, the generated policies mathematically provably converge to a (potentially small) neighborhood of the optimal policy under mild conditions, despite the imprecise information in the learning process. The mechanism directly synthesizes the policies from the sensory data, without identifying an internal forward model. Our preliminary computational results on two classic arm reaching tasks are in line with experimental observations reported in the literature. The model-free control principle proposed in the paper sheds more lights into the inherent robustness of human sensorimotor systems to the imprecise information, especially control-dependent noise, in the CNS. [ABSTRACT FROM AUTHOR]

Functional arm reaching involves multilinked joints: shoulder, elbow, and wrist. We propose that induced position analysis is a useful analytical tool for multijoint coordination of arm reaching. This method was used to compute the contributions of the net joint moment to the hand position when reaching forward. We describe the method and give examples of validating this model with motion capture data. The shoulder and elbow were prime movers of the arm: both acted together with an "overshoot" and "undershoot" pattern respectively to move the hand forward into the final position. [ABSTRACT FROM AUTHOR]

Stroke individuals frequently have balance problems and impaired arm movements that affect their daily activities. We investigated the influence of target uncertainty and the side of the brain lesion on the performance of arm movements and postural adjustments during reaching in a standing position by stroke individuals. Participants stood on force plates and reached a target displayed on the center of a monitor screen under conditions differentiated by the prior knowledge of the target location at the beginning of the movement. Individuals who had a stroke in the right side of the brain performed the tasks with the ipsilesional, right upper limb while the individuals with a left stroke performed with the ipsilesional, left upper limb. Healthy individuals performed with right and left limbs, which data were later averaged for statistical analysis. Kinematic analysis of the arm and lower limb joints and displacements of the center of pressure of each lower limb were compared between target conditions and groups. Stroke individuals showed larger center of pressure displacements of the contralesional compared to the ipsilesional limb while these displacements were symmetrical between lower limbs for the healthy individuals, regardless of the target condition. The target uncertainty affected both the characteristics of the arm movements and postural adjustments before movement onset. Right stroke individuals used more ankle joint movements under the uncertain compared to the certain condition. The uncertainty in target location affects the arm reaching in upright standing, but the effects depend on the side of the brain lesion. [ABSTRACT FROM AUTHOR]

When reaching towards an object while standing, one’s hand responds very quickly to visual perturbations such as the target being displaced or the background moving. Such responses require postural adjustments. When the background moves, its motion might be attributed to self-motion in a stable world, and thereby induce compensatory postural adjustments that affect the hand. The changes in posture associated with a given hand movement response may, therefore, be different for the two types of perturbations. To see whether they are, we asked standing participants to move their hand in the sagittal direction away from their body to targets displayed on a horizontal screen in front of them. The target displacements and background motion were in the lateral direction. We found hand movement responses that were in line with earlier reports, with a latency that was slightly shorter for target displacements than for background motion, and that was independent of target displacement size or background motion speed. The trunk responded to both perturbations with a modest lateral sway. The two main findings were that the upper trunk responded even before the hand did so and that the head responded to background motion but hardly responded to target displacements. These findings suggest that postural adjustments associated with adjusting the hand movement precede the actual adjustments to the movement of the hand, while at the same time, participants try to keep their head stable on the basis of visual information. [ABSTRACT FROM AUTHOR]

Two basic trade-offs interact while our brain decides how to move our body. First, with the cost-benefit trade-off, the brain trades between the importance of moving faster toward a target that is more rewarding and the increased muscular cost resulting from a faster movement. Second, with the speed-accuracy trade-off, the brain trades between how accurate the movement needs to be and the time it takes to achieve such accuracy. So far, these two trade-offs have been well studied in isolation, despite their obvious interdependence. To overcome this limitation, we propose a new model that is able to simultaneously account for both trade-offs. The model assumes that the central nervous system maximizes the expected utility resulting from the potential reward and the cost over the repetition of many movements, taking into account the probability to miss the target. The resulting model is able to account for both the speed-accuracy and the cost-benefit trade-offs. To validate the proposed hypothesis, we confront the properties of the computational model to data from an experimental study where subjects have to reach for targets by performing arm movements in a horizontal plane. The results qualitatively show that the proposed model successfully accounts for both cost-benefit and speed-accuracy trade-offs.

The present study aimed to investigate the influence of target height on the symmetry and amplitude of the postural adjustments assessed by the displacements of the center of pressure (COP) before and during the unilateral, arm movements in the upright position. Thirteen young, right-handed adults stood with each foot on one force platform and reached a target placed at one of three heights displayed on a monitor screen. The performance of the right arm movements (movement time and radial error), amplitude of the COP displacements of each lower limb and the percentage of body weight loading on the right lower limb before and during the reaching movements were compared across target heights conditions. Postural adjustments were symmetrical prior but asymmetrical after movement onset. Effect of target height was observed on the postural adjustments before and during the movements (i.e., amplitudes of the COP displacements increased for the higher target), mainly for the right limb. The arm performance was similar across target heights. The findings of the present study suggested that postural adjustments are dependent on the target heights to ensure success in the arm movements. [ABSTRACT FROM AUTHOR]

Two basic trade-offs interact while our brain decides how tomove our body. First, with the cost-benefit trade-off, the brain trades between the importance of moving faster toward a target that is more rewarding and the increased muscular cost resulting from a faster movement. Second, with the speed-accuracy trade-off, the brain trades between how accurate the movement needs to be and the time it takes to achieve such accuracy. So far, these two trade-offs have been well studied in isolation, despite their obvious interdependence. To overcome this limitation, we propose a new model that is able to simultaneously account for both trade-offs. The model assumes that the central nervous system maximizes the expected utility resulting from the potential reward and the cost over the repetition of many movements, taking into account the probability to miss the target. The resulting model is able to account for both the speed-accuracy and the cost-benefit trade-offs. To validate the proposed hypothesis, we confront the properties of the computational model to data from an experimental study where subjects have to reach for targets by performing arm movements in a horizontal plane. The results qualitatively show that the proposed model successfully accounts for both cost-benefit and speed-accuracy trade-offs. [ABSTRACT FROM AUTHOR]

Introduction: Moving the arm towards an object is a complex task. Movements of the arm joints must be well coordinated in order to obtain a smooth and accurate hand trajectory. Most studies regarding reaching movements address young subjects. Coordination differences in the neural mechanism underlying motor control throughout the life stages is yet unknown. The understanding of these changes can lead to a better comprehension of neuromotor pathologies and therefore to more suitable therapies. Methods: Our purpose was to investigate interjoint coordination in three different aging groups (children, young, elderly). Kinematics and kinetics specific variables were analyzed focusing on defined parameters to get insight into arm coordination. Intersegmental dynamics was used to calculate shoulder and elbow torques assuming a 2-link segment model of the upper extremity (upper arm and forearm) with two friction-less joints (shoulder and elbow). A virtual reality environment was used to examine multidirectional planar reaching in three different directions (randomly presented). Results: Seven measures were computed to investigate group interlimb differences: shoulder and elbow muscle torques (peak and impulse), work performed by shoulder and elbow joints, maximum velocity, movement distance, distance error at final position, movement duration and acceleration duration. Our data analysis showed differences between movement performances for all analyzed variables, at all ages. Conclusion: We found that the intersegmental dynamics for the interlimb (left/right) comparisons were similar for the elderly and children groups as compared to the young. In addition, the coordination and control of motor tasks changes during life, becoming less effective in old age. [ABSTRACT FROM AUTHOR]

Background Several species of the New World monkeys have been used as experimental models in biomedical and neurophysiological research. However, a method for controlled arm reaching tasks has not been developed for these species. New method We have developed a fully automated, pneumatically driven, portable, and reconfigurable experimental apparatus for arm-reaching tasks suitable for these small primates. Results We have utilized the apparatus to train two owl monkeys in a visually-cued arm-reaching task. Analysis of neural recordings demonstrates directional tuning of the M1 neurons. Comparison with existing method(s) Our apparatus allows automated control, freeing the experimenter from manual experiments. Conclusion The presented apparatus provides a valuable tool for conducting neurophysiological research on New World monkeys. [ABSTRACT FROM AUTHOR]

The authors previously reported that asymmetrical patterns of hand preference are updated and modified by present sensorimotor conditions. They examined whether participation in long-term training in the upper extremity sport fencing might modify arm selection and performance asymmetries. Eight fencers and eight nonfencers performed reaching movements under 3 experimental conditions: (a) nonchoice right, (b) nonchoice left, and (c) choice, either right or left arm as selected by subject. The nonchoice conditions allowed assessment of potential interlimb differences in movement performance, while the choice condition allowed assessment of the frequency and pattern of arm selection across subject groups. Our findings showed that the athlete group showed substantially greater symmetry in the performance and selection measures. These findings suggest that arm selection and performance asymmetries can be altered by intense long-term practice. [ABSTRACT FROM PUBLISHER]

Background/aim: Patients with stroke who are suffering from impaired reaching movement experience insufficient spatial and temporal coordination, affecting upper limb functions and everyday life tasks. This study examines a new robot-assisted rehabilitation method for ameliorating arm reaching movements through velocity error enhancement training. The authors hypothesised that this robot-assisted rehabilitation training may encourage restoration of arm reaching abilities among poststroke hemiparesis patients. Methods: Several clinical and kinematic measures were used to evaluate outcomes. Subjects were assigned either to an experimental group that underwent 5-week treatments with error enhanced forces, or to a control group that received passive treatment. The control group undertook reaching tasks over the same period while they were connected to the robot but without it applying any error enhancement forces to their upper limb. The robotic system was programmed based on previous kinematic data from healthy subjects, so any deviation from the relatively smooth, calculated, optimal trajectory, and velocity profile mean encountered error enhancing external forces. Results: The results showed an appreciable effect on smoothness and regularity of movement. After 5 weeks of velocity error enhancement treatment, all subjects in the experimental group displayed movements converging towards their optimal profiles, together with decreased variability in path trajectory. In contrast to the control group, their mean deviation was also significantly reduced. These positive changes in motor control patterns were paralleled by gains in functional capacity, as reflected by the Motor Assessment Scale test results. However, those results should be carefully inspected in regard to small sample size and un-matching of motor performance at the beginning of the trial between groups. Conclusion: The study demonstrates the potential of robotic rehabilitation that combines error enhancement and velocity component training to help stroke patients. [ABSTRACT FROM AUTHOR]

Abstract: Oscillatory activities in the brain within the beta (15–30Hz) and gamma (70–90Hz) ranges have been implicated in the generation of voluntary movement. However, their roles remain unclear. Here, we record local field potential activity from the region of the subthalamic nucleus during movement of the contralateral limb in 11 patients with Parkinson''s disease. Patients were on their normal dopaminergic medication and were cued to perform arm-reaching movements after a delay period at three different speeds: ‘slow’, ‘normal’, and ‘fast’. Beta activity desynchronized earlier in response to the cue indicating an upcoming fast reach than to the cues for slow or normal speed movement. There was no difference in the degree of beta desynchronization between reaching speeds and beta desynchronization was established prior to movement onset in all cases. In contrast, synchronization in the gamma range developed during the reaching movement, and was especially pronounced during fast reaching. Thus the timing of suppression in the beta band depended on task demands, whereas the degree of increase in gamma oscillations depended on movement speed. These findings point to functionally segregated roles for different oscillatory frequencies in motor preparation and performance. [Copyright &y& Elsevier]

Reaching movements made to targets during exposure to passive constant velocity rotation show significant endpoint errors. By contrast, reaching movements made during voluntary rotation of the torso are accurate. In both cases, as a consequence of the simultaneous motion of the arm and the torso, Coriolis forces are generated on the arm tending to deflect its path. Our goal in the present paper was to determine whether during voluntary torso rotations arm movement accuracy is preserved by feed forward compensations for self-generated Coriolis forces. To test this hypothesis we analyzed and quantified the contribution of torso rotation and translation to arm dynamics and compared the kinematics and kinetics of pointing movements during voluntary and passive torso rotation. Coriolis torques at the shoulder increase nearly sixfold in voluntary turn and reach movements relative to reaches made without torso rotation, yet are equally accurate. Coriolis torques during voluntary turn and reach movements are more than double those produced by reaching movements during passive body rotation at 60°/s. Nevertheless, the endpoints of the reaches made during voluntary rotation are not deviated, but those of reaches made during passive rotation are deviated in the direction of the Coriolis forces generated during the movements. We conclude that there is anticipatory pre-programmed compensation for self-generated Coriolis forces during voluntary torso rotation contingent on intended torso motion and arm trajectory. [ABSTRACT FROM AUTHOR]

Abstract: Positron emission tomography (PET) was used to investigate differences in neural plasticity associated with learning a unique motor task in patients with schizophrenia and healthy volunteers. Working with a robotic manipulandum, subjects learned reaching movements in a force field. Visual cues were provided to guide the reaching movements. PET rCBF measures were acquired while participants learned the motor skill over successive runs. The groups did not differ in behavioral performance but did differ in their rCBF activity patterns. Healthy volunteers displayed blood flow increases in primary motor cortex and supplementary motor area with motor learning. The patients with schizophrenia displayed an increase in the primary visual cortex with motor learning. Changes in these regions were positively correlated with changes in each group''s motor accuracy, respectively. This is the first study to employ a unique arm-reaching motor learning test to assess neural plasticity during multiple phases of motor learning in patients with schizophrenia. The patients may have an inability to rapidly tune motor cortical neural populations to a preferred direction. The visual system, however, appears to be highly compensated in schizophrenia and the inability to rapidly modulate the motor cortex may be substantially corrected by the schizophrenic group''s visuomotor adaptations. [Copyright &y& Elsevier]

A technique is described that characterizes the dynamics of the interjoint coordination of arm reaching movements in healthy subjects (n=10) and in patients who had sustained a left-sided cerebrovascular accident (n=18). All participants were right-handed. Data from the affected right arm of patients with stroke were compared with those from the right arm of healthy subjects. Seated subjects made 25 pointing movements in a single session. Movements were made from an initial target located ipsilaterally to the right arm beside the body, to a final target located in front of the subject in the contralateral arm workspace. Kinematic data from the finger, wrist, elbow, both shoulders and sternum were recorded in three dimensions at 200 Hz with an optical tracking system. Analysis of interjoint coordination was based on the patterns of temporal delay between rotations at two adjacent joints (shoulder and elbow). The data were reduced to a single graph (Temporal Coordination or TC index) integrating the essential temporal characteristics of joint movement (the angular displacements, velocities and timing). TC segments, duration and amplitude, were analysed. The analysis was sensitive to the differences in interjoint coordination between healthy subjects and patients with arm motor deficits. In patients, the temporal coordination between elbow and shoulder movements was disrupted from the middle to the end of the reach. More specifically, in mid-reach, all patients had difficulty coordinating elbow flexion with shoulder horizontal adduction. In addition, patients with severe arm hemiparesis had difficulty changing elbow movement direction from flexion to extension and in coordinating this change with shoulder movement. At the end of the reach, patients with severe hemiparesis had deficits in the execution of elbow extension while all patients had impaired coordination of elbow extension and shoulder horizontal adduction. In addition, active ranges of joint motions were significantly decreased in the stroke compared to the healthy subjects. Finally, TC analysis revealed significant relationships between specific aspects of disrupted interjoint coordination and the level of motor impairment, suggesting that it may be a useful tool in the identification of specific movement coordination deficits in neurological impaired populations that can be targeted in treatment for arm motor recovery. [ABSTRACT FROM AUTHOR]

Abstract Background Virtual reality (VR) is an innovative tool for sensorimotor rehabilitation increasingly being employed in clinical and community settings. Despite the growing interest in VR, few studies have determined the validity of movements made in VR environments with respect to real physical environments. The goal of this study was to compare movements done in physical and virtual environments in adults with motor deficits to those in healthy individuals. Methods The participants were 8 healthy adults and 7 adults with mild left hemiparesis due to stroke. Kinematics of functional arm movements involving reaching, grasping and releasing made in physical and virtual environments were analyzed in two phases: 1) reaching and grasping the ball and 2) ball transport and release. The virtual environment included interaction with an object on a 2D computer screen and haptic force feedback from a virtual ball. Temporal and spatial parameters of reaching and grasping were determined for each phase. Results Individuals in both groups were able to reach, grasp, transport, place and release the virtual and real ball using similar movement strategies. In healthy subjects, reaching and grasping movements in both environments were similar but these subjects used less wrist extension and more elbow extension to place the ball on the virtual vertical surface. Participants with hemiparesis made slower movements in both environments compared to healthy subjects and during transport and placing of the ball, trajectories were more curved and interjoint coordination was altered. Despite these differences, patients with hemiparesis also tended to use less wrist extension during the whole movement and more elbow extension at the end of the placing phase. Conclusion Differences in movements made by healthy subjects in the two environments may be explained by the use of a 2D instead of a 3D virtual environment and the absence of haptic feedback from the VR target. Despite these differences, our findings suggest that both healthy subjects and individuals with motor deficits used similar movement strategies when grasping and placing a ball in the two reality conditions. This suggests that training of arm movements in VR environments may be a valid approach to the rehabilitation of patients with motor disorders.

Introduction: In this proof-of-concept study, we introduce a custom-developed robot-assisted training protocol, named "Assist-As-Asked", aiming at improving arm function of chronic stroke subjects with moderate-to-severe upper extremity motor impairment. The study goals were to investigate the feasibility and potential adverse effects of this training protocol in both physical and virtual environments., Methods: A sample of convenience of four chronic stroke subjects participated in 10 half-hour sessions. The task was to practice reaching six targets in both virtual and physical environments. The robotic arm used the Assist-As-Asked paradigm in which it helped subjects to complete movements when asked by them. Changes in the kinematics of the reaching movements and the participants' perception of the reaching practice in both environments were the outcome measures of interest., Results: Subjects improved their reaching performance and none of them reported any adverse events. There were no differences between the two environments in terms of kinematic measures even though subjects had different opinions about the environment preference., Conclusions: Using the Assist-As-Asked protocol in moderate-to-severe chronic stroke survivors is feasible and it can be used with both physical and virtual environments with no evidence of one of them to be superior to the other based on users' perspectives and movement kinematics., (© The Author(s) 2020.)

A correction to the article related to unifying speed accuracy and cost benefit trade off in the human movements is presented.

Background: Advances in wearable sensor technology now allow us to quantify the number, type and kinematic characteristics of bouts of infant arm movement made across a full day in the natural environment. Our aim here was to determine whether the amount and kinematic characteristics of arm movements made across the day in the natural environment were related to developmental status in infants with typical development as they learned to reach for objects using their arms. Methods: We used wearable sensors to measure arm movement across days and months as infants developed arm reaching skills. In total, 22 infants with typical development participated, aged between 38 and 203 days. Of the participants, 2 infants were measured once and the other 20 infants were measured once per month for 3 to 6 visits. The Bayley Scales of Infant Development was used to measure developmental level. Results: Our main findings were: 1) infant arm movement characteristics as measured by full-day wearable sensor data were related to Bayley motor, cognitive and language scores, indicating a relationship between daily movement characteristics and developmental status; 2) infants who moved more had larger increases in language and cognitive scores across visits; and 3) larger changes in movement characteristics across visits were related to higher motor scores. Conclusions: This was a preliminary, exploratory, small study of the potential importance of infant arm movement characteristics as measured by full-day wearable sensor data. Our results support full-day arm movement activity as an area of interest for future study as a biomarker of neurodevelopmental status and as a target for early intervention., Competing Interests: No competing interests were disclosed.