Force Tracking Task Research Articles

IMPACT OF FINGERTIP ACTIONS ON TOTAL POWER OF SURFACE ELECTROMYOGRAPHY FROM EXTRINSIC HAND MUSCLES

Quantizing the relationship between finger force and multitendoned extrinsic hand muscles could be useful for understanding the control strategies that underlie the coordination of finger movements and forces. The objective of this study is to explore the relationship of fingertip force production and total power of surface electromyography (sEMG) recorded on extrinsic hand muscles under isometric voluntary contraction. Thirteen healthy volunteers were recruited to participate in this study. In the designed force-tracking tasks, all volunteers were required to produce a certain force with either index finger or middle finger to match the target force for 5 s. Meanwhile, the sEMG signals were acquired from two extrinsic hand muscles: extensor digitorum (ED) and flexor digitorum superficialis (FDS). For each trial, sEMG of the effective force segment was extracted; then, the power spectrum was estimated based on autoregressive (AR) model and from which the corresponding total power of sEMG was computed. The experimental results reveal that the total power of sEMG linearly increases with force level regardless of the task finger and extrinsic hand muscle. It is also found that the total power obtained from index finger is significantly less than that of middle finger for FDS at the same force level (p < 0.05), while this kind of statistical significance cannot be found for ED. However, with respect to the measurement of total power, the type of extrinsic hand muscle has not exhibited significantly different contribution to the task finger under a certain fingertip force level. The findings of this study indicate that the total power of the extrinsic hand muscle's sEMG can be used to characterize finger's activities.

Affected and unaffected quantitative aspects of grip force control in hemiparetic patients after stroke

Adequate grip force modulation is critical to manual dexterity and often impaired in hemiparetic stroke patients. Previous studies in hemiparetic patients suggest that aspects of grip force control may be differently affected by the lesion. We developed a visuomotor power grip force-tracking task allowing quantification of tracking error, force variability and release duration. We investigated force control in 24 chronic stroke patients with varying severity of hemiparesis and in healthy control subjects. Force tracking was performed at 10, 20, and 30% maximal voluntary contraction (MVC). Control subjects were also tested at absolute force levels similar to those of the patients.Patients tracking with their paretic hand at similar relative (%MVC) grip force levels showed increased error, force variability and release duration, but surprisingly, there was no difference in tracking error or variability between patients and control subjects performing at similar absolute force levels. Furthermore, patients improved their tracking performance across repeated blocks similar to control subjects. Release duration, however, was increased (also in the non-paretic hand), was force-independent and did not correlate with MVC strength. Of the three performance measures, only release duration explained some of the variance in arm and hand function (Frenchay Arm Test score), independent of MVC strength. The findings show (i) that hemiparetic stroke patients preserve the ability to modulate (generate and maintain) power grip force within their limited force range and (ii) that MVC grip strength and duration of grip release are differently affected and are two complementary predictors of arm function after stroke.

A Generalized Multivariate Autoregressive (GmAR)-Based Approach for EEG Source Connectivity Analysis

Studying brain connectivity has provided new insights to the understanding of brain function. While connectivity measures are conventionally computed from electroencephalogram (EEG) signals directly, the presence of volume conduction represents a serious confound affecting interpretation of results. A common solution is to use a two-stage approach which involves estimating underlying brain sources from scalp EEG recordings and subsequently estimating the connectivity between the inferred sources. Recently, a state-space framework which jointly models the instantaneous mixing effects of volume conduction and the causal relationships between underlying brain sources is proposed. In this paper, we extend the state-space framework and model the source activity by a generalized multivariate autoregressive (mAR) process with possibly non-Gaussian noise. A maximum likelihood estimation approach is developed which allows simultaneous estimation of both the mixing matrix and AR model parameters directly from scalp EEG. The proposed technique was verified with simulated EEG data generated using the single-shell spherical head model and demonstrated improved estimation accuracies compared to conventional two-stage connectivity estimation approaches. Furthermore, the proposed technique was applied to EEG data collected from normal and Parkinson's subjects performing a right-handed force-tracking task with differing amounts of visual feedback. The partial directed coherence (PDC) between sources showed significant differences between groups and conditions. These results suggest that the proposed technique is a powerful method to extract connectivity information from EEG recordings.

Modulation of somatosensory processing in dual tasks: an event-related brain potential study

The amplitudes of the event-related brain potentials (ERPs) have been associated with the amount of attentional resources. The present study investigated whether force production type (increasing or decreasing force) in a visuomotor force tracking task modulates the ERPs elicited in a somatosensory oddball task performed simultaneously, whether stimulus-response coupling assessed by a single-trial analysis of P300 latency is modulated by the concurrent performance of the tasks, and whether dynamic visuomotor coordination rather static coordination is sensitive to the ERP modulation. In the dual-task condition, the subjects tracked a target line moving on the display with another line representing the force generated by the grip of their left hand, while executing the somatosensory oddball task with the right hand. In the oddball-only condition, the oddball task only was performed. The amplitude of the P300 elicited in the oddball task was decreased in the dual-task condition compared with the oddball-only condition, and further decreased in the force-decreasing phase compared with the increasing phase, but was not altered by the concurrently performed isometric contraction. P100, N140, reaction time (RT), and error rate were not influenced by force production type. A correlation analysis of single-trial P300 latency and RT showed that the dual-task condition produced a stronger coupling of the P300 and RT. In summary, different force production types requiring dynamic visuomotor coordination alter a modality-nonspecific late stage of somatosensory processing but have less of an effect on early stages. During the performance of the dual task, stimulus-response coupling in the somatosensory discrimination task becomes stronger to compensate for a lack of resources and/or due to snap decisions owing to sufficient resources.

Impact of precision grip tasks on cervical spinal network excitability in humans

Motor skill acquisition in the lower limb may induce modifications of spinal network excitability. We hypothesized that short-term motor adaptation in precision grip tasks would also induce modifications of cervical spinal network excitability. In a first series of experiments, we studied the impact of two different precision grip force control tasks (a visuomotor force-tracking task and a control force task without visual feedback) on cervical spinal network excitability in healthy subjects. We separately tested the efficacy of two key components of the spinal circuitry: (i) presynaptic inhibition on flexor carpi radialis (FCR) Ia terminals, and (ii) disynaptic inhibition directed from extensor carpi radialis (ECR) to FCR. We found that disynaptic inhibition decreased temporarily after both force control tasks, independently of the presence of visual feedback. In contrast, the amount of presynaptic inhibition on FCR Ia terminals decreased only after the visuomotor force tracking task. This temporary decrease was correlated with improved tracking accuracy during the task (i.e. short-term motor adaptation). A second series of experiments confirmed these results and showed that the visuomotor force-tracking task resulted also in an increase of the Hmax/Mmax ratio and the slope of the ascending part of the H-reflex recruitment curve. In order to address the role of presynaptic inhibition in the motor adaptation process, we conducted a third series of experiments during which presynaptic inhibition was recorded before and after two consecutive sessions of visuomotor force tracking. The results showed that (i) improved tracking accuracy occurred during both sessions, and (ii) presynaptic inhibition decreased only after the first session of visuomotor force tracking. Taken together, these results suggest thus that the nature of the motor task performed has a specific impact on the excitability of these cervical spinal circuits. These findings also suggest that early motor adaptation is associated with a modulation of presynaptic Ia inhibition in the upper limb.

The Loss of Dexterity in the Bilateral Lower Extremities in Patients With Stroke

The aim of this study was to examine the dexterity of both lower extremities in patients with stroke. Twenty patients with stroke and 20 age-matched control subjects participated in this study. To determine the dexterity of the lower extremities, we examined the ability to control muscle force during submaximal contractions in the knee extensor muscles using a force tracking task. The root mean square errors were calculated from the difference between the target and response force. The root mean square error was significantly greater in the affected limb of patients with stroke compared with those of the unaffected limb and the control subjects, and in the unaffected limb compared with that of the control subjects. Furthermore, the root mean square error of the affected limb was related significantly to motor function as determined by Fugl-Myer assessment. These results demonstrate impairment of the dexterity of both the affected and the unaffected lower extremities in patients with stroke.

Assessment of Fine Motor Control in Individuals with Parkinson's Disease Using Force Tracking with a Secondary Cognitive Task

Motor symptoms of Parkinson's disease (PD) are typically assessed using clinical scales such as the Unified Parkinson's Disease Rating Scale, but clinical scales are insensitive to subtle changes early in the disease process. The goal of this project was to use current sensing technology to develop a quantitative assessment tool to document fine motor deficits in PD based on the ability to control grip force output. The assessment was designed to challenge deficits commonly encountered as a result of PD, including dual-task performance of a motor task and a cognitive task simultaneously. Two force sensors were used to measure the isometric pinch grip force between the thumb and index finger in 30 individuals with PD and 30 control participants of similar age without disability. Participants performed a target force tracking task with each of two different target waveforms (sinusoidal or pseudorandom) under each of three different cognitive load conditions (none, subtract 1, and subtract 3). Dependent variables calculated from the force sensor data included root mean square error, tremor integral, and lag. In general, individuals with PD showed significantly less accuracy in generating the target forces as shown by larger root mean square error compared with controls (P < 0.001). They also showed greater amounts of tremor and lag compared with controls (P = 0.001 and <0.001, respectively). Deficits were more pronounced during the cognitive multitasking component of the test. These results will serve as a preliminary work for the development of a clinical biomarker for PD that may help to identify subtle deficits in fine motor control early in the disease process and facilitate tracking of disease progression with time.

Reversing cognitive–motor impairments in Parkinson’s disease patients using a computational modelling approach to deep brain stimulation programming

Deep brain stimulation in the subthalamic nucleus is an effective and safe surgical procedure that has been shown to reduce the motor dysfunction of patients with advanced Parkinson's disease. Bilateral subthalamic nucleus deep brain stimulation, however, has been associated with declines in cognitive and cognitive-motor functioning. It has been hypothesized that spread of current to nonmotor areas of the subthalamic nucleus may be responsible for declines in cognitive and cognitive-motor functioning. The aim of this study was to assess the cognitive-motor performance in advanced Parkinson's disease patients with subthalamic nucleus deep brain stimulation parameters determined clinically (Clinical) to settings derived from a patient-specific computational model (Model). Data were collected from 10 patients with advanced Parkinson's disease bilaterally implanted with subthalamic nucleus deep brain stimulation systems. These patients were assessed off medication and under three deep brain stimulation conditions: Off, Clinical or Model based stimulation. Clinical stimulation parameters had been determined based on clinical evaluations and were stable for at least 6 months prior to study participation. Model-based parameters were selected to minimize the spread of current to nonmotor portions of the subthalamic nucleus using Cicerone Deep Brain Stimulation software. For each stimulation condition, participants performed a working memory (n-back task) and motor task (force tracking) under single- and dual-task settings. During the dual-task, participants performed the n-back and force-tracking tasks simultaneously. Clinical and Model parameters were equally effective in improving the Unified Parkinson's disease Rating Scale III scores relative to Off deep brain stimulation scores. Single-task working memory declines, in the 2-back condition, were significantly less under Model compared with Clinical deep brain stimulation settings. Under dual-task conditions, force tracking was significantly better with Model compared with Clinical deep brain stimulation. In addition to better overall cognitive-motor performance associated with Model parameters, the amount of power consumed was on average less than half that used with the Clinical settings. These results indicate that the cognitive and cognitive-motor declines associated with bilateral subthalamic nucleus deep brain stimulation may be reversed, without compromising motor benefits, by using model-based stimulation parameters that minimize current spread into nonmotor regions of the subthalamic nucleus.

Toward the Restoration of Hand Use to a Paralyzed Monkey: Brain-Controlled Functional Electrical Stimulation of Forearm Muscles

Loss of hand use is considered by many spinal cord injury survivors to be the most devastating consequence of their injury. Functional electrical stimulation (FES) of forearm and hand muscles has been used to provide basic, voluntary hand grasp to hundreds of human patients. Current approaches typically grade pre-programmed patterns of muscle activation using simple control signals, such as those derived from residual movement or muscle activity. However, the use of such fixed stimulation patterns limits hand function to the few tasks programmed into the controller. In contrast, we are developing a system that uses neural signals recorded from a multi-electrode array implanted in the motor cortex; this system has the potential to provide independent control of multiple muscles over a broad range of functional tasks. Two monkeys were able to use this cortically controlled FES system to control the contraction of four forearm muscles despite temporary limb paralysis. The amount of wrist force the monkeys were able to produce in a one-dimensional force tracking task was significantly increased. Furthermore, the monkeys were able to control the magnitude and time course of the force with sufficient accuracy to track visually displayed force targets at speeds reduced by only one-third to one-half of normal. Although these results were achieved by controlling only four muscles, there is no fundamental reason why the same methods could not be scaled up to control a larger number of muscles. We believe these results provide an important proof of concept that brain-controlled FES prostheses could ultimately be of great benefit to paralyzed patients with injuries in the mid-cervical spinal cord.

CHARACTERIZATION OF FINGER ISOMETRIC FORCE PRODUCTION WITH MAXIMUM POWER OF SURFACE ELECTROMYOGRAPHY

Finger's action has been controlled by both intrinsic and extrinsic hand muscles. Characterizing the finger action with the activations of hand muscles could be useful for evaluating the neuromuscular control strategy of finger's motor functions. This study is designed to explore the correlation of isometric fingertip force production and frequency-domain features of surface electromyography (sEMG) recorded on extrinsic hand muscles. To this end, 13 subjects (five male and eight female university students) have been recruited to conduct a target force-tracking task. Each subject is required to produce a certain level of force with either the index or middle fingertip to match the pseudo-random ordered target force level (4N, 6N, or 8N) as accurate as possible. During the finger force production process, the sEMG signals are recorded on two extrinsic hand muscles: flex digitorum superficials (FDS) and extensor digitorum (ED). For each sEMG trail, the power spectrum is estimated with the autoregressive (AR) model and from which the maximum power is obtained. Our experimental results reveal three findings: (1) the maximum power increases with the force level regardless of the force producing finger (i.e. index or middle) and the extrinsic hand muscle (i.e. FDS or ED). (2) The sEMG maximum power of index finger is significantly lower than that of the middle finger under the same force level and extrinsic hand muscle. (3) No significant difference can be found between the maximum powers of FDS and ED. The results indicate that the activations of the extrinsic muscles are affected by both the force level and the force producing finger. Based on our findings, the sEMG maximum power of the extrinsic hand muscles could be used as a key parameter to describe the finger's actions.

Improved Motor Function And Cortical Activation In Parkinson'S Disease Patients Following Acute Forced-exercise

In previous studies, we have shown that a long-term lower extremity forced-exercise intervention (8 weeks) resulted in significant improvements in upper and lower extremity motor function of mild to moderate Parkinson's disease (PD) patients. The global nature of motor improvements suggest that forced-exercise may result in changes in central nervous system functioning. PURPOSE: To determine the motor and cortical effects of an acute bout of forced-exercise in a group of PD patients. METHODS: Motor function and functional magnetic resonance imaging (MRI) examinations were completed, in six mild to moderate PD patients, under two randomized conditions: no exercise and three hours after forced-exercise. The forced-exercise intervention consisted of one 40-minute session in which patients exercised on stationary tandem cycle with an able-bodied trainer. The trainer maintained a pedaling rate between 80-90 revolutions per minute which was approximately 35 percent faster than the patient's voluntary pedaling rate (60 revolutions per minute). Functional MRI analysis of changes in cortical activation volume was compared after forced-exercise to no exercise. RESULTS: Clinical motor function, assessed with the Unified Parkinson's disease Rating Scale-III, was nearly 40 percent better following forced-exercise compared to the no-exercise condition. During functional MRI scanning patients performed a force-tracking task in which they matched a projected sinusoidal or constant line. Motor performance was 35 percent better following forced-exercise compared to no exercise. Increases in cortical activation were most prominent in the supplementary motor area (SMA) after forced exercise in comparison to the no exercise state. This increase in activation was a general observation across tasks performed with each limb. CONCLUSION: Improvements in upper extremity function and increased levels of activation within cortical structures such as the SMA indicate that forced-exercise may facilitate central motor control processes in Parkinson's disease patients.

Precision in isometric precision grip force is reduced in middle-aged adults

We investigated age related changes in the control of precision grip in 29 healthy adults spanning early adulthood to middle age (21-67 years). Subjects performed a visually guided, isometric precision grip ramp-and-hold force-tracking task. Target force levels were 3, 6, and 9 N. Precision and performance of force regulation was quantified. Larger errors were made during the ramp than during the hold phase. Age correlated positively with the amount of error at the lowest (3 N) force level in both phases. Force onsets were systematically earlier in middle-aged subjects and the average slope of the force during the ramp decreased with increasing age. The results show that precision during low grip force control decreases already during middle age and those subjects may modify their force generation strategies to compensate for early and subtle degenerative changes in the motor system before decline in grip strength is apparent.

Bilateral subthalamic stimulation impairs cognitive-motor performance in Parkinson's disease patients

Deep brain stimulation (DBS) is a surgical procedure that has been shown effective in improving the cardinal motor signs of advanced Parkinson's disease, however, declines in cognitive function have been associated with bilateral subthalamic nucleus (STN) DBS. Despite the fact that most activities of daily living clearly have motor and cognitive components performed simultaneously, postoperative assessments of cognitive and motor function occur, in general, in isolation of one another. The primary aim of this study was to determine the effects of unilateral and bilateral STN DBS on upper extremity motor function and cognitive performance under single- and dual-task conditions in advanced Parkinson's disease patients. Data were collected from eight advanced Parkinson's disease patients between the ages of 48 and 70 years (mean 56.5) who had bilaterally placed STN stimulators. Stimulation parameters for DBS devices were optimized clinically and were stable for at least 6 months prior to study participation. Data were collected while patients were Off anti-parkinsonian medications under three stimulation conditions: Off stimulation, unilateral DBS and bilateral DBS. In each stimulation condition patients performed a cognitive (n-back task) and motor (force tracking) task under single- and dual-task conditions. During dual-task conditions, patients performed the n-back and force-maintenance task simultaneously. Under relatively simple dual-task conditions there were no differences in cognitive or motor performance under unilateral and bilateral stimulation. As dual-task complexity increased, cognitive and motor performance was significantly worse with bilateral compared with unilateral stimulation. In the most complex dual-task condition (i.e. 2-back + force tracking), bilateral stimulation resulted in a level of motor performance that was similar to the Off stimulation condition. Significant declines in cognitive and motor function under modest dual-task conditions with bilateral but not with unilateral STN DBS suggest that unilateral procedures may be an alternative to bilateral DBS for some patients, in particular, those with asymmetric symptomology. From a clinical perspective, these results underscore the need to assess cognitive and motor function simultaneously during DBS programming as these conditions may better reflect the context in which daily activities are performed.

Error processing during online motor control depends on the response accuracy

We investigated which brain areas show error-related activity during online motor control while errors occur independently from decision making. During motor tasks, error is a deviation from accuracy or correctness. The effect of the accuracy level on error-related brain activity is unclear. Using functional Magnetic Resonance Imaging (fMRI), we investigated how error-related brain activity, especially in fronto-medial wall areas, depended on motor accuracy (MA). Subjects performed a force tracking task with the thumb–index grip: to continuously follow a moving target on a monitor with a cursor which position was controlled by the force amount produced by the fingers. Task difficulty varied with changes in the cursor size (the smaller the cursor, the more difficult the task). We measured the motor accuracy (mean distance between the cursor center and the target) and the error amount (cursor out of the target). Errors were produced when motor accuracy was low and also when motor accuracy was high. For fMRI data processing, we defined a model based on both the error amount and the motor accuracy. The results showed that supplementary motor area (SMA) and dorsal anterior cingulate cortex (ACC) activation increased with error and task difficulty independent of the accuracy of motor control. Interestingly, activity in the rostral part of left ACC only increased with error when the motor accuracy was low, independently from task difficulty. These results suggest a clear functional dissociation between dorsal and rostral ACC in error processing which depends on the amount of attentional resources allocated to motor accuracy.

A behaviour study of the effects of visual feedback on fluctuating isometric force production with force tracking tasks

The primary goal of this study is to explore the impacts of visual feedback gain and the force varying rate on the continuously fluctuating isometric force production. Twelve recruited participants have been instructed to complete the handgrip tasks that require the participant to control his or her grip force level to track a moving target bar which is proportional to the real-time force production. Two visual feedback gain levels and two force varying rates have been tested. The results show that high visual feedback gain and force varying rate will lead to larger errors of force production. Keywords: visual feedback; gain; force production; Fitts’ law.

Multi-Fingered Grasping and Manipulation in Virtual Environments Using an Isometric Finger Device

In this article we present a new isometric input device for multi-fingered grasping in virtual environments. The device was designed to simultaneously assess forces applied by the thumb, index, and middle finger. A mathematical model of grasping, adopted from the analysis of multi-fingered robot hands, was applied to achieve multi-fingered interaction with virtual objects. We used the concept of visual haptic feedback where the user was presented with visual cues to acquire haptic information from the virtual environment. The virtual object corresponded dynamically to the forces and torques applied by the three fingers. The application of the isometric finger device for multi-fingered interaction is demonstrated in four tasks aimed at the rehabilitation of hand function in stroke patients. The tasks include opening the combination lock on a safe, filling and pouring water from a glass, muscle strength training with an elastic torus, and a force tracking task. The training tasks were designed to train patients' grip force coordination and increase muscle strength through repetitive exercises. The presented virtual reality system was evaluated in a group of healthy subjects and two post-stroke patients (early post-stroke and chronic) to obtain overall performance results. The healthy subjects demonstrated consistent performance with the finger device after the first few trials. The two post-stroke patients completed all four tasks, however, with much lower performance scores as compared to healthy subjects. The results of the preliminary assessment suggest that the patients could further improve their performance through virtual reality training.

Age-related Differences in Working Memory and Force Control under Dual-task Conditions

ABSTRACT The aim of this study was to investigate the relationship between force control and cognitive performance under dual-task conditions in younger (18–22 years) and older adults (65–77 years). Cognitive (n-back test) and motor performance (force-tracking) was measured independently and simultaneously. Results indicated overall age-related differences for the n-back and the force-tracking task. Age-related differences increased during dual-task conditions. While younger adults exhibited no decrease in cognitive or motor performance during dual-task conditions, older adults showed a decrease in motor and cognitive performance. Additionally, when older adults made an error in the cognitive task they tended to show greater variability in the force-tracking task. These results suggest that cognitive motor deficits are responsible for older adults' performance decrements under dual-task conditions.

MR compatible force sensing system for real-time monitoring of wrist moments during fMRI testing

Functional magnetic resonance imaging (fMRI) of brain function is used in neurorehabilitation to gain insight into the mechanisms of neural recovery following neurological injuries such as stroke. The behavioral paradigms involving the use of force motor tasks utilized in the scanner often lack the ability to control details of motor performance. They are often limited by subjectiveness, lack of repeatability, and complexity that may exclude evaluation of patients with poor function. In this paper we describe a novel MR compatible wrist device that is capable of measuring isometric forces generated at the hand and joint moments along wrist flexion–extension and wrist ulnar–radial deviation axes. Joint moments measured by the system can be visually displayed to the individual and used during target matching block or event related paradigms. Through a small set of pilot testing both inside and outside the MR environment, we have found that the force tracking tasks and performance in the scanner are reproducible, and that high quality force and moment recordings can be made during fMRI studies without compromising the fMRI images. Furthermore, the device recordings are extremely sensitive making it possible for individuals with poor hand and wrist function to be tested.

자율 주행 이동 로봇의 슬립을 고려한 횡방향 임피던스 힘제어에 대한 연구

In this paper, lateral force control of a mobile robot with slip is presented. First, the bicycle model of a mobile robot is derived for the front steering. Second, impedance force control algorithm is applied to regulate contact force with environment. The desired distance is specified conservatively inside the environment to guarantee to make contact. Different stiffness of environment has been tested for force tracking task. Simulation results show that the proposed control algorithm works well to maintain desired contact force on the environment.

Age-related changes in grasping force modulation

The aim of this study was to determine the effect of age on the modulation of forces produced by the digits and to determine the effects of practice on the control of these forces in young and older adults. Young (n = 14, 19-28 years) and old (n = 12, 67-75 years) adults used a precision grip to perform a variable force-tracking task (sine wave, 5-25% of maximum voluntary force) with their dominant hand. Participants performed 100 practice trials over 2 consecutive days. Results indicated that both groups improved accuracy of force tracking as a result of practice. Younger adults performed the task at a higher level in pre- and post-test conditions compared with older adults. Younger adults showed improvements in force control in force generation and release phases. Older adults reached performance levels comparable with younger adults' pre-test performance, but only after extended practice. In contrast to young adults, older adults' performance during the force release phases remained quite variable. These data suggest that older adults are impaired in the accurate release of grip force. Varied force release patterns that disrupt the precision of force modulation may contribute to older adults' diminished dexterous abilities.