Initial Movement Direction Research Articles

Sensitivity of Cerebellar Reaching Ataxia to Kinematic and Dynamic Demands.

Individuals with cerebellar ataxia often face significant challenges in controlling reaching, especially when multijoint movements are involved. This study investigated the effects of kinematic and dynamic demands on reaching movements by individuals with cerebellar ataxia and healthy controls using a virtual reality task. Participants reached to target locations designed to elicit a range of coordination strategies between shoulder and elbow joint movements. Results showed that the cerebellar group exhibited greater trajectory curvature and variability in hand paths compared to controls, with pronounced deficits in the initial hand movement direction. Kinematic simulations indicated that early hand movement errors were sensitive to the required onset times and rates of joint movements and were most impaired when opposite direction joint movements were required (e.g., elbow extension with shoulder flexion). This highlights significant disruptions in motion planning and feedforward control in the cerebellar group. Dynamic analysis showed that cerebellar participants' movements were more impaired in reaching directions where interaction torques normally assist the desired elbow and shoulder movements, which required them to rely more on muscle torques to move. These reach directions were also those that required opposite direction joint movements. Overall, our data suggest that reaching deficits in cerebellar ataxia result from 1) the early-phase motion planning deficits that worsen with tight timing requirements and 2) the inability to compensate for interaction torques, particularly when they assist the intended movement.

Humans flexibly use visual priors to optimize their haptic exploratory behavior

Humans can use prior information to optimize their haptic exploratory behavior. Here, we investigated the usage of visual priors, which mechanisms enable their usage, and how the usage is affected by information quality. Participants explored different grating textures and discriminated their spatial frequency. Visual priors on texture orientation were given each trial, with qualities randomly varying from high to no informational value. Adjustments of initial exploratory movement direction orthogonal to the textures’ orientation served as an indicator of prior usage. Participants indeed used visual priors; the more so the higher the priors’ quality (Experiment 1). Higher task demands did not increase the direct usage of visual priors (Experiment 2), but possibly fostered the establishment of adjustment behavior. In Experiment 3, we decreased the proportion of high-quality priors presented during the session, hereby reducing the contingency between high-quality priors and haptic information. In consequence, even priors of high quality ceased to evoke movement adjustments. We conclude that the establishment of adjustment behavior results from a rather implicit contingency learning. Overall, it became evident that humans can autonomously learn to use rather abstract visual priors to optimize haptic exploration, with the learning process and direct usage substantially depending on the priors’ quality.

A pilot study: effect of somatosensory loss on motor corrections in response to unknown loads in a reaching task by chronic stroke survivors.

Despite recent studies indicating a significant correlation between somatosensory deficits and rehabilitation outcomes, how prevailing somatosensory deficits affect stroke survivors' ability to correct their movements and recover overall remains unclear. To explore how major deficits in somatosensory systems impede stroke survivors' motor correction to various external loads, we conducted a study with 13 chronic stroke survivors who had hemiparesis. An inertial, elastic, or viscous load, which was designed to impose perturbing forces with various force profiles, was introduced unexpectedly during the reaching task using a programmable haptic robot. Participants' proprioception and cutaneous sensation were also assessed using passive movement detection, finger-to-nose, mirror, repositioning, and Weinstein pressure tests. These measures were then analyzed to determine whether the somatosensory measures significantly correlated with the estimated reaching performance parameters, such as initial directional error, positional deviation, velocity deviations, and speed of motor correction were measured.Of 13 participants, 5 had impaired proprioception, as they could not recognize the passive movement of their elbow joint, and they kept showing larger initial directional errors even after the familiarization block. Such continuously found inaccurate initial movement direction might be correlated with the inability to develop the spatial body map especially for calculating the initial joint torques when starting the reaching movement. Regardless of whether proprioception was impaired or not, all participants could show the stabilized, constant reaching movement trajectories. This highlights the role of proprioception especially in the execution of a planned movement at the early stage of reaching movement.

Propagating spatiotemporal activity patterns across macaque motor cortex carry kinematic information

Propagating spatiotemporal neural patterns are widely evident across sensory, motor, and association cortical areas. However, it remains unclear whether any characteristics of neural propagation carry information about specific behavioral details. Here, we provide the first evidence for a link between the direction of cortical propagation and specific behavioral features of an upcoming movement on a trial-by-trial basis. We recorded local field potentials (LFPs) from multielectrode arrays implanted in the primary motor cortex of two rhesus macaque monkeys while they performed a 2D reach task. Propagating patterns were extracted from the information-rich high-gamma band (200 to 400Hz) envelopes in the LFP amplitude. We found that the exact direction of propagating patterns varied systematically according to initial movement direction, enabling kinematic predictions. Furthermore, characteristics of these propagation patterns provided additional predictive capability beyond the LFP amplitude themselves, which suggests the value of including mesoscopic spatiotemporal characteristics in refining brain-machine interfaces.

Planning and Executing Aiming Movements in Middle Childhood.

Harmonious voluntary movements require efficiency in their planning and execution. Throughout middle childhood structural changes in the central nervous and musculoskeletal systems influence these processes and resultant motor behavior. In this study, we evaluated the characteristics of the motor planning and executing of aiming movements directed at targets located in different positions in space in children aged 7, 9, and 11years. We divided 43 right-handed children, into three age groups and instructed them to perform aiming movements directed at targets using a stylus on a digital tablet. The children performed the movement with their dominant upper limbs from a starting point towards targets positioned ipsilaterally or contralaterally to this dominant limb. We analyzed temporal and spatial variables of motor performance. Younger (7-year-old) children made more errors in the initial movement direction and more frequently corrected their movements during task execution when compared to 9- and 11-year-old children who did not differ from each other. All age groups were similar in movement accuracy and precision. Movements toward contralateral targets were slower and more accurate than movements toward ipsilateral targets for all groups. These results show that performing aiming movements develop with the onset of middle childhood.

Different planning policies for the initial movement velocity depending on whether the known uncertainty is in the cursor or in the target: Motor planning in situations where two potential movement distances exist.

During goal-directed behaviors, individuals can be required to start a movement before deciding on the final goal. Previous studies have focused on the initial movement direction in situations involving multiple targets in different directions from the starting position and have shown that the movement is initiated in the average direction among the target directions. However, the previous studies only included situations with targets at equivalent distances, and the characteristics of motor planning in situations with multiple movement possibilities over different potential distances are unclear. In such situations, movement velocity is another important control variable. Furthermore, while previous studies examined situations with an uncertain motor target position, uncertainty can also exist in the effector position (e.g., body or tool locations). Therefore, we examined (1) whether the average output is confirmed in the initial movement velocity during execution in situations involving two potential movements with different distances. In addition, we examined (2) whether planning of the movement velocity can differ depending on the presence of uncertainty in the cursor or the target. In the main conditions, the participants were required to start a reaching movement with two potential movement distances; in the two-cursor condition, two cursors were presented before the start of the trial, and in the two-target condition, two targets were presented. As a control condition, a distance condition corresponding to each main condition was also performed. In the control condition, the initial movement velocity varied linearly with distance. Then, we tested whether the initial movement velocity in situations with two potential movement distances would follow the averaging output of the corresponding control condition. The results revealed that while the initial movement velocity in the two-target condition was slower than the averaging output, that in the two-cursor condition approached the averaging output. These results suggest that the velocity profile of the goal-directed movement is not simply averaged in a situation where two potential targets exist, and that there is a difference in the planning policy of the initial movement depending on whether the known uncertainty is for the movement goal or the effector.

A numerical study on the thermocapillary migration of a droplet under microgravity with periodic thermal boundaries using the front-tracking method

This paper mainly studied the thermocapillary migration of deformable droplets induced by periodic temperature boundary under microgravity conditions. The finite-difference/front-tracking (FD/FT) method was used to solve the Navier–Stokes equation coupled with the energy equation, and the continuum surface force (CSF) model was used to simplify the surface tension of the phase interface. The results showed that the maximum droplet migration velocity increased with the increase of temperature amplitude, and the droplet cycle period became shorter with the increase of temperature angular frequency. In the 1/4 cycle, the initial movement time of droplet decreased with the increase of temperature phase. If the phase was reversed, the initial movement direction of the droplet changed. With the increase of Reynolds number (Re), the droplet tended to maintain its motion inertia.

Determination of Fault Type of Lombok Earthquakes from July 1 to December 31, 2018, using Focal Mechanism Method

Research has been conducted on determining the type of fault in Lombok earthquake on July 1 to December 31 2018 using the focal mechanism method. The focal mechanism is a method of reviewing fault parameters that include strike, dip and rake based on the initial movement direction of P wave recorded by the station, which then projected into a focal ball. There are 246 stations are used in several countries. There were 139 earthquakes with M?4.0 on July 1 to December 31 2018, at coordinates 7.0? S-9.0? S and 115.5? E-117.5? E. The result of fault field parameters is at nodal 1 strike=52?-149?, dip=6?-75?, rake=39?-143? and at nodal 2, strike=233?-313?, dip=18?-84?, rake=58?-119?, then projected into focus ball. Based on these results shows that earthquakes occur as a result of thrust fault movement.

Simulation of the dynamic processes of a low-capacity combine harvester movement

To automate the process of harvesting crops, different types of harvesting machines are required. The most common type of machines used to automate ingathering are harvesters. The use of harvesters for collecting grain crops is rational in fields from 2 hectares. On smaller areas it is not profitable and difficult to apply. For applications in small areas, low-capacity harvesters with a throughput of the thresher up to 1 kg/s (small-sized) may be suitable. The purpose of this study is to analyze the cushioning mass control system of a low-capacity unmanned combine harvester using computer simulation, as well as the simulation of directional stability and turning. To calculate vertical vibrations in the Matlab/Simulink software package, a model of a cushioning system for a wheeled agricultural combine was prepared. In the same software package, simulation of directional stability and turning implementation was carried out. The parameters of vibration displacement, vibration velocity and acceleration, as well as the vibration frequency indicators on the operator's seat are determined. Comparison of the simulation results of the initial and corrected direction of movement of the harvester showed that for this model the maximum deviation from the planned path is a maximum of 10%, which is within acceptable limits. The maximum deviation of the harvester from the course does not exceed the permissible values, which is acceptable accuracy to ensure directional stability.

Evaluation of the characteristics of on-call search for violators using unmanned aircraft flight

Evaluation of the characteristics of search for violators on an on-call basis with the use of unmanned aircraft flight on conditions that the initial coordinates and direction of movement of a border violator are known has been conducted. Assessment of unmanned aircraft flight capabilities in an on-call mode while searching for trespassers has been carried out for the first time. The essence of scientific novelty consists in determining the width of the semicircular tacks and their number, the radius of tacks trajectory during search for violators in an on-call mode as well as the number of tacks and their maximum number. This enables working out of the suggestions regarding the choice of UAV’s and their use in finding violators after receiving the signals from technical means used in guarding of extended sectors of the border. Conditions of the search for violators under limited time of unmanned aircraft flight, which also affects selection of the search mode on an on-call basis, have been determined. It was determined the total time of unmanned aircraft flight is least influenced factor of restriction the trajectory tacks number of searching by unmanned aircraft in accordance with data mentioned.

Competition between movement plans increases motor variability: evidence of a shared resource for movement planning.

Do movement plans, like representations in working memory, share a limited pool of resources? If so, the precision with which each individual movement plan is specified should decrease as the total number of movement plans increases. To explore this, human participants made speeded reaching movements toward visual targets. We examined if preparing one movement resulted in less variability than preparing two movements. The number of planned movements was manipulated in a delayed response cueing procedure that limited planning to a single target (experiment 1) or hand (experiment 2) or required planning of movements toward two targets (or with two hands). For both experiments, initial movement direction variability was higher in the two-plan condition than in the one-plan condition, demonstrating a cost associated with planning multiple movements, consistent with the limited resource hypothesis. In experiment 3, we showed that the advantage in initial variability of preparing a single movement was present only when the trajectory could be fully specified. This indicates that the difference in variability between one and two plans reflects the specification of full motor plans, not a general preparedness to move. The precision cost related to concurrent plans represents a novel constraint on motor preparation, indicating that multiple movements cannot be planned independently, even if they involve different limbs.

Learning feedback and feedforward control in a mirror-reversed visual environment.

When we learn a novel task, the motor system needs to acquire both feedforward and feedback control. Currently, little is known about how the learning of these two mechanisms relate to each other. In the present study, we tested whether feedforward and feedback control need to be learned separately, or whether they are learned as common mechanism when a new control policy is acquired. Participants were trained to reach to two lateral and one central target in an environment with mirror (left-right)-reversed visual feedback. One group was allowed to make online movement corrections, whereas the other group only received visual information after the end of the movement. Learning of feedforward control was assessed by measuring the accuracy of the initial movement direction to lateral targets. Feedback control was measured in the responses to sudden visual perturbations of the cursor when reaching to the central target. Although feedforward control improved in both groups, it was significantly better when online corrections were not allowed. In contrast, feedback control only adaptively changed in participants who received online feedback and remained unchanged in the group without online corrections. Our findings suggest that when a new control policy is acquired, feedforward and feedback control are learned separately, and that there may be a trade-off in learning between feedback and feedforward controllers.

Effective force control by muscle synergies.

Muscle synergies have been proposed as a way for the central nervous system (CNS) to simplify the generation of motor commands and they have been shown to explain a large fraction of the variation in the muscle patterns across a variety of conditions. However, whether human subjects are able to control forces and movements effectively with a small set of synergies has not been tested directly. Here we show that muscle synergies can be used to generate target forces in multiple directions with the same accuracy achieved using individual muscles. We recorded electromyographic (EMG) activity from 13 arm muscles and isometric hand forces during a force reaching task in a virtual environment. From these data we estimated the force associated to each muscle by linear regression and we identified muscle synergies by non-negative matrix factorization. We compared trajectories of a virtual mass displaced by the force estimated using the entire set of recorded EMGs to trajectories obtained using 4–5 muscle synergies. While trajectories were similar, when feedback was provided according to force estimated from recorded EMGs (EMG-control) on average trajectories generated with the synergies were less accurate. However, when feedback was provided according to recorded force (force-control) we did not find significant differences in initial angle error and endpoint error. We then tested whether synergies could be used as effectively as individual muscles to control cursor movement in the force reaching task by providing feedback according to force estimated from the projection of the recorded EMGs into synergy space (synergy-control). Human subjects were able to perform the task immediately after switching from force-control to EMG-control and synergy-control and we found no differences between initial movement direction errors and endpoint errors in all control modes. These results indicate that muscle synergies provide an effective strategy for motor coordination.

Misjudgment of direction contributes to curvature in movements toward haptically defined targets.

The trajectories of arm movements toward visually defined targets are curved, even if participants try to move in a straight line. A factor contributing to this curvature may be that participants systematically misjudge the direction to the target, and try to achieve a straight path by always moving in the perceived direction of the target. If so, the relation between perception of direction and initial movement direction should not only be present for movements toward visually defined targets, but also when making movements toward haptically defined targets. To test whether this is so, we compared errors in the initial movement direction when moving as straight as possible toward haptically defined targets with errors in a pointer setting task toward the same targets. We found a modest correlation between perception of direction and initial movement direction for movements toward haptically defined targets. The amount of correlation depended on the geometry of the task.

Haptic guidance interferes with learning to make movements at an angle to stimulus direction

Haptic guidance has been shown to interfere with learning a novel visuo-motor rotation. Here, we ask whether this interference is specific to the learning of visuo-motor transformations or whether it is a more generalized phenomenon of learning spatial movement characteristics. Participants practiced to make movements at an angle of 75° relative to target directions with and without haptic path guidance. Test trials without guidance and without visual feedback revealed poorer performance after haptic guidance practice than in the no-guidance control group, even though during guided practice movement directions were more accurate than during unguided practice. The more precise directions during guided practice were associated with shorter movement latencies than in the control group, suggesting an incomplete rotation of the movement direction relative to the direction of the visual target. A detailed analysis of the first few millimeters of each movement revealed that the initial movement direction was indeed rotated too little, and the correct direction was adopted only gradually under the influence of haptic guidance. These findings support the perspective on motor learning as a process that is driven by consequent improvements of performance and that is compromised by factors that serve to improve performance even without learning. Haptic guidance is one such factor.

Accounting for direction and speed of eye motion in planning visually guided manual tracking

Accurate motor planning in a dynamic environment is a critical skill for humans because we are often required to react quickly and adequately to the visual motion of objects. Moreover, we are often in motion ourselves, and this complicates motor planning. Indeed, the retinal and spatial motions of an object are different because of the retinal motion component induced by self-motion. Many studies have investigated motion perception during smooth pursuit and concluded that eye velocity is partially taken into account by the brain. Here we investigate whether the eye velocity during ongoing smooth pursuit is taken into account for the planning of visually guided manual tracking. We had 10 human participants manually track a target while in steady-state smooth pursuit toward another target such that the difference between the retinal and spatial target motion directions could be large, depending on both the direction and the speed of the eye. We used a measure of initial arm movement direction to quantify whether motor planning occurred in retinal coordinates (not accounting for eye motion) or was spatially correct (incorporating eye velocity). Results showed that the eye velocity was nearly fully taken into account by the neuronal areas involved in the visuomotor velocity transformation (between 75% and 102%). In particular, these neuronal pathways accounted for the nonlinear effects due to the relative velocity between the target and the eye. In conclusion, the brain network transforming visual motion into a motor plan for manual tracking adequately uses extraretinal signals about eye velocity.

Sensory-Motor Deficits in Children with Fetal Alcohol Spectrum Disorder Assessed Using a Robotic Virtual Reality Platform

Fetal alcohol spectrum disorder (FASD) is associated with a large number of cognitive and sensory-motor deficits. In particular, the accurate assessment of sensory-motor deficits in children with FASD is not always simple and relies on clinical assessment tools that may be coarse and subjective. Here we present a new approach: using robotic technology to accurately and objectively assess motor deficits of children with FASD in a center-out reaching task. A total of 152 typically developing children and 31 children with FASD, all aged between 5 and 18 were assessed using a robotic exoskeleton device coupled with a virtual reality projection system. Children made reaching movements to 8 peripheral targets in a random order. Reach trajectories were subsequently analyzed to extract 12 parameters that had been previously determined to be good descriptors of a reaching movement, and these parameters were compared for each child with FASD to a normative model derived from the performance of the typically developing population. Compared with typically developing children, the children with FASD were found to be significantly impaired on most of the parameters measured, with the greatest deficits found in initial movement direction error. Also, children with FASD tended to fail more parameters than typically developing children: 95% of typically developing children failed fewer than 3 parameters compared with 69% of children with FASD. These results were particularly pronounced for younger children. The current study has shown that robotic technology is a sensitive and powerful tool that provides increased specificity regarding the type of motor problems exhibited by children with FASD. The high frequency of motor deficits in children with FASD suggests that interventions aimed at stimulating and/or improving motor development should routinely be considered for this population.

Following and intercepting scribbles: interactions between eye and hand control

The smooth pursuit eye movement system appears to be importantly engaged during the planning and execution of interceptive hand movements. The present study sought to probe the interaction between eye and hand control systems by examining their responses during an interception task that included target speed perturbations. On 2/3 of trials, the target increased or decreased speed at various times, ranging from about 300ms before to 150ms after the onset of a finger movement directed to intercept the target and was triggered by a GO signal. Additionally, the same 2D sum-of-sines target trajectories were followed with the eyes without interception. The smooth pursuit system responded more quickly if the target speed perturbation occurred earlier during the reaction time (i.e., near the time of the GO signal). Similarly, the finger movement began more quickly if target speed was increased earlier during the reaction time. For early perturbation conditions, the initial direction of the finger movement matched the predicted target intercept using the new target speed. For perturbations occurring after finger movement, onset initial direction of finger movement did not match target interception such that the finger path began to curve toward the perturbed target after about 150-200ms. The results support the idea of an active process of visual target path extrapolation simultaneously used to guide both the eye and hand.

Radiation Damage Effects by Molecular Dynamics Simulation in ${\rm BaTiO}_{3}$ Ferroelectric Crystal

Perovskite ferroelectrics have high endurance to radiation. In order to understand the mechanism at the atomic level, molecular dynamics simulation is applied to investigate the process of defects generation and displacement cascades in ${\rm BaTiO}_{3}$ crystal. The calculated average threshold displacement energy of O, Ba and Ti atom is 53 eV, 70 eV, and 119 eV, respectively, so the number of O defects is larger than that of Ba and Ti defects. Furthermore, the simulations show that the initial movement direction of the primary knock-on atom (PKA) has significant influence on the number of defects because of different collision type (glancing collisions or direct knocks), and the number of Frenkel defects does not simply increase with increasing PKA energy due to the annealing effect. This investigation of the collision cascades is helpful to understand the radiation damage in ${\rm BaTiO}_{3}$ crystal and may offer useful guidelines to the design and applications for the practical devices.

Effect of visuomotor-map uncertainty on visuomotor adaptation

Vision and proprioception contribute to generating hand movement. If a conflict between the visual and proprioceptive feedback of hand position is given, reaching movement is disturbed initially but recovers after training. Although previous studies have predominantly investigated the adaptive change in the motor output, it is unclear whether the contributions of visual and proprioceptive feedback controls to the reaching movement are modified by visuomotor adaptation. To investigate this, we focused on the change in proprioceptive feedback control associated with visuomotor adaptation. After the adaptation to gradually introduce visuomotor rotation, the hand reached the shifted position of the visual target to move the cursor to the visual target correctly. When the cursor feedback was occasionally eliminated (probe trial), the end point of the hand movement was biased in the visual-target direction, while the movement was initiated in the adapted direction, suggesting the incomplete adaptation of proprioceptive feedback control. Moreover, after the learning of uncertain visuomotor rotation, in which the rotation angle was randomly fluctuated on a trial-by-trial basis, the end-point bias in the probe trial increased, but the initial movement direction was not affected, suggesting a reduction in the adaptation level of proprioceptive feedback control. These results suggest that the change in the relative contribution of visual and proprioceptive feedback controls to the reaching movement in response to the visuomotor-map uncertainty is involved in visuomotor adaptation, whereas feedforward control might adapt in a manner different from that of the feedback control.