Static Task Research Articles

Effects of antiparasitic treatment on dynamically and statically tested cognitive skills over time

The main objective of this work was to investigate two testing procedures, repeated static tests and dynamic testing, that can more clearly demonstrate the impact of treatment for parasites in children. Rural Tanzanian children were assessed for the presence/absence and burden of helminth parasites and assigned to one of three groups—infected/treated with anthelmintic medication, infected/not treated, and uninfected/not treated. All three groups were assessed with dynamically administered cognitive tests (on three separate occasions, with each session including pretest, instruction, and posttest), conventionally (statically) administered cognitive tests, and traditionally administered educational achievement tests. The data demonstrated that the children in the infected/treated and uninfected groups showed higher cognitive gains on two out of three dynamically administered and one out of eight statically administered tasks than did the children in the infected/not treated group. Thus, anthelmintic medications for parasitic illnesses appear to contribute to the improvement in cognitive functioning and this improvement is captured more clearly in dynamic than static tasks. The pathways of this improvement are still not understood and require further investigation.

Progressive suppression of intracortical inhibition during graded isometric contraction of a hand muscle is not influenced by hand preference

GABAergic intracortical inhibition (ICI) in human motor cortex (M1) assists fractionated activation of muscles, and it has been suggested that hemispheric differences in ICI may contribute to hand preference. Previous studies of this issue have all been conducted at rest, with conflicting results. Testing during voluntary activation may reveal functionally relevant differences. In normal subjects, we assessed (1) operation of ICI circuits during selective activation of an intrinsic hand muscle at different forces, and (2) whether this differs between right and left hemispheres. Surface EMG was recorded bilaterally from abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles in eleven right-handed subjects. A circular coil applied paired transcranial magnetic stimulation (TMS) with posteriorly directed current in the brain. Conditioning intensity was 0.8 x active threshold and interstimulus interval was 3 ms. TMS was applied to right or left M1 while subjects were at rest or performing isometric thumb abduction at different forces (0.5, 1, 2, 3, 5 and 10 N) with the contralateral hand. Conditioning TMS was less effective at suppressing the muscle evoked potential in APB during 2-10 N thumb abduction (P < 0.0001) versus rest, but not with lower target forces (0.5, 1 N). Conditioning TMS was less effective for FDI and ADM only during 10 N thumb abduction. We conclude that differential modulation of ICI in M1 during selective muscle activation is a function of target isometric force level. At low forces (<5% MVC), ICI is not modulated for the corticospinal neurons controlling the active or inactive muscles. There is a progressive reduction of ICI effects on corticospinal neurons at higher forces, which is largely restricted to corticospinal neurons controlling the muscle targeted for activation over the range of forces tested (up to approximately 25% MVC). The pattern of ICI modulation with selective voluntary muscle contraction was similar in left and right hemispheres during this relatively simple static task. If hemispheric differences in operation of M1 ICI circuits contribute to hand preference, a more challenging finger movement protocol may be needed to demonstrate this asymmetry.

Muscle coordination in complex movements during Jeté in skilled ballet dancers

The principal goal of our study is to gain an insight into the coordinative structure of a complex body movement. As a first step, this paper describes the activity of multiple skeletal muscles associated with the drawing-like movements that resemble the Jeté, performed by skilled ballet dancers. The EMG activity of 18 muscles of the trunk, pelvis, and both legs was recorded when dancers standing on the left leg moved the toe of the right leg forward and backward along a straight line. A major finding is that the EMG activity of all right muscles, despite their functional and anatomical diversity, was minimised not only at the initial, vertical position but also in the reversal phase of movement when the moving leg was maximally deviated from the vertical position. In other words, the activity was minimal when torques of the weights of limb segments were minimal as well as when these torques were maximal. In contrast, in the static task when the maximally deviated leg position was maintained, there was substantial tonic activation of leg muscles, an activity that was necessary to balance these torques. The result is consistent with the hypothesis that movements of the body result from centrally induced changes in the muscle recruitment thresholds influencing the referent configuration of the body. The existence of minima in the overall EMG activity of skeletal muscles is not the only prediction of the referent configuration hypothesis. An immediate consequence of the hypothesis is that, in movements of the limb, the EMG patterns should be a direction-dependent phenomenon known as "directional tuning" of muscles. In combination with the principle of minimal interaction of neuromuscular system, the referent configuration hypothesis offers a dynamic approach to the problems of how control levels may guide multi-muscle and multi-joint systems without redundancy problems.

Torque Levels, Subjective Discomfort, and Muscle Activity Associated with Four Commercially Available Screwdrivers under Static and Dynamic Work Conditions

This study evaluated screwdrivers with different handle designs and blade lengths. 10 men and 10 women voluntarily participated. A repeated-measures experiment design was employed. The three independent factors were sex of user, handle (four types), and blade length (130, 170, and 210 mm). The dependent measures were the maximum supination torque under a static task and the %MVC of EMG responses in biceps brachii and flexor digitorum, and a discomfort rating for the upper extremity under the dynamic task. Analysis showed that the in-line screwdriver with the combined characteristics of large handle diameter (3.8-4.1 cm), smooth rubber covering handle surface, triangular (or circular) shape, and adequate handle length (11 cm) had the greatest supination torque and a smaller discomfort rating than the screwdriver with the pistol-grip handle. Blade length was not significantly related to any dependent measure.

전역 이기종 환경에서의 정적 태스크 스케줄링의 비교 연구

전역 이기종 환경에서의 정적 태스크 스케줄링의 비교 연구

Muscle fatigue and endurance during repetitive intermittent static efforts: development of prediction models

Localized muscle fatigue has received growing attention as a potential design variable and exposure metric in research towards prevention of musculoskeletal disorders in the workplace. While fatigue during sustained static work has been investigated extensively, effects during tasks comprising work–rest cycles are less clear. Work–rest models for static intermittent work have been presented in several reports, but the applicability is often limited to specific conditions. A study was conducted that facilitated a description of the relationships between static intermittent efforts and muscle endurance and fatigue. Exercises consisted of 1 h (maximum) of repetitive static arm abductions, involving a range of muscle contraction levels (10–30% maximum voluntary exertion), duty cycles (0.2–0.8) and cycle times (20–180 s). A between-subject central composite experimental design was used and 15 different exercise conditions were examined with six participants (three females and three males) for each. Along with endurance times, temporal changes related to fatigue were monitored using muscle strength, ratings of discomfort and electromyography (EMG) obtained from the middle-deltoid muscle during the contraction phase of the work cycles. The results of this study showed the influence of contraction level and duty cycle on the majority of fatigue measures used, while cycle time tended to affect EMG spectral measures. Using a response surface methodology, several fatigue prediction models and contour plots were developed that can be employed as an aid for design and evaluation of light repetitive static tasks. Good correspondence was generally found between discomfort rating and other measures of fatigue, suggesting the usefulness of this measure for rapid assessments of local fatigue in the workplace.

Assessment of the occlusion technique as a means for evaluating the distraction potential of driver support systems

Driver distraction is a safety-critical issue that has been bought to greater public attention with the recent developments of more advanced driver support systems (DSS), e.g. navigation systems. Such systems have the potential to distract drivers significantly from the primary task of controlling their vehicle, potentially resulting in an accident. DSS developers need to be able to assess distraction potential in the early stages of design. In this respect, the occlusion technique and its associated measures are claimed to be reliable indicators of potential visual demand. In particular, it has been argued that the technique provides more information than other economical methods based on task time whilst stationary (static task time), such as the ‘15-second rule’. To investigate these assertions, a study compared results from an occlusion assessment and a road-based assessment. Sixteen drivers carried out two tasks using two user-interfaces under three conditions: statically, full vision, statically, restricted vision (occlusion), and whilst driving. Occlusion was found to be a valid technique. In particular, it may be used to distinguish between tasks based on their level of visual demand. It is concluded that occlusion offers advantages over other methods but requires a robust prototype for results to be meaningful.

Gross Motor Function Measure for children with cerebral palsy

The aim of this study was to compare the pattern of motor dysfunction in Hong Kong Chinese children with spastic diplegic and the athetoid type of cerebral palsy (CP) by the Gross Motor Function Measure (GMFM). The GMFM was first tested on its content validity in differentiating the items suitable for testing on upper and lower limb function, followed by test-retest and inter-rater reliability studies, before it was used in a within-subject experiment comparing upper and lower gross motor function in two types of CP, respectively. Children with spastic diplegia (n=18) and with athetosis (n=19) were recruited from three pre-school centres, schools for physically handicapped children and centres of the Hong Kong Spastic Association in Hong Kong. The GMFM, a standardized outcome measure of the motor function in children with CP, was used in comparing mean scores of motor tasks involving upper limbs and those not involving upper limbs in the athetoid and spastic cerebral palsied children. The scores were significantly higher for the children in the spastic diplegic group, but there was no significant difference in the performance of static and dynamic motor tasks of the GMFM between the children in the two groups.

Visualization of Multidigit Manipulation Mechanics: Manipulation Mechanics

The purpose of this paper is to develop a visualization tool for the investigation of the contact mechanics at the object-digit interface and force coordination among multiple digits during manipulation tasks. Five miniature six-component force/torque transducers, mounted on a custom-made instrumented handle, were used to record force/torque data at the tips of individual digits during five-digit manipulation tasks. A digitizing device was used to obtain three-dimensional (3-D) coordinates of anatomical landmarks of the hand for the construction of a hand geometric model. The 3-D hand model and force data from transducers were transformed to a common handle coordinate frame so that force vectors were superimposed on digit-tips. One subject performed three static manipulation tasks (grasping, rotating, and lifting) with maximum voluntary contraction on the stabilized instrumented handle. The magnitude and orientation of the force vectors of individual digits were dependent on the tasks, and the subject tended to maximize task efficiency by utilizing different force coordination strategies for different tasks. The visualization methods developed in this paper could potentially provide an effective tool for the examination of object-digit interaction mechanics and interdigit force coordination.

Neuromuscular Biomechanical Modeling to Understand Knee Ligament Loading

This article examines our use of EMG-driven neuromuscular biomechanical models to study how muscles stabilize the knee. EMG can be used to establish which activation patterns are used by people for knee stabilization. However, it does not reveal the effectiveness of these patterns. The EMG-driven models provide quantitative comparisons of the effectiveness of the different knee-stabilizing activation patterns. Subjects performed static tasks and common sporting maneuvers that challenged knee joint stability. EMG, joint posture and motion, and external forces and moments were measured during these tasks. These data were used to calibrate the EMG-driven neuromuscular biomechanical model. We then used the model to predict the role of muscles in supporting varus and valgus moments at the knee. We found specific muscle activation patterns to support varus and valgus moments. The most potent activation pattern to stabilize the knee is when the hamstrings or quadriceps are required to generate flexion or extension moments, respectively. The next most effective knee-stabilizing pattern is cocontraction of the hamstring and quadriceps. The small biarticular muscles at the knee provided the least support of varus and valgus moments. In the sporting tasks, sidestepping was found to place the anterior cruciate ligament at high risk of injury. We found that the muscles are the main defense against knee ligament injuries in these tasks. Traditional biomechanical and neurophysiological methods have shown that there are specific activation patterns used to stabilize the knee. By also using the EMG-driven neuromuscular biomechanical model, we have shown how effective muscles are in stabilizing the knee. This modeling method provides a new tool to understand knee joint stabilization.

Evolutionary training of hardware realizable multilayer perceptrons

The use of multilayer perceptrons (MLP) with threshold functions (binary step function activations) greatly reduces the complexity of the hardware implementation of neural networks, provides tolerance to noise and improves the interpretation of the internal representations. In certain case, such as in learning stationary tasks, it may be sufficient to find appropriate weights for an MLP with threshold activation functions by software simulation and, then, transfer the weight values to the hardware implementation. Efficient training of these networks is a subject of considerable ongoing research. Methods available in the literature mainly focus on two-state (threshold) nodes and try to train the networks by approximating the gradient of the error function and modifying appropriately the gradient descent, or by progressively altering the shape of the activation functions. In this paper, we propose an evolution-motivated approach, which is eminently suitable for networks with threshold functions and compare its performance with four other methods. The proposed evolutionary strategy does not need gradient related information, it is applicable to a situation where threshold activations are used from the beginning of the training, as in “on-chip” training, and is able to train networks with integer weights.

Enhanced and diminished visuo-spatial information processing in autism depends on stimulus complexity

Visuo-perceptual processing in autism is characterized by intact or enhanced performance on static spatial tasks and inferior performance on dynamic tasks, suggesting a deficit of dorsal visual stream processing in autism. However, previous findings by Bertone et al. indicate that neuro-integrative mechanisms used to detect complex motion, rather than motion perception per se, may be impaired in autism. We present here the first demonstration of concurrent enhanced and decreased performance in autism on the same visuo-spatial static task, wherein the only factor dichotomizing performance was the neural complexity required to discriminate grating orientation. The ability of persons with autism was found to be superior for identifying the orientation of simple, luminance-defined (or first-order) gratings but inferior for complex, texture-defined (or second-order) gratings. Using a flicker contrast sensitivity task, we demonstrated that this finding is probably not due to abnormal information processing at a sub-cortical level (magnocellular and parvocellular functioning). Together, these findings are interpreted as a clear indication of altered low-level perceptual information processing in autism, and confirm that the deficits and assets observed in autistic visual perception are contingent on the complexity of the neural network required to process a given type of visual stimulus. We suggest that atypical neural connectivity, resulting in enhanced lateral inhibition, may account for both enhanced and decreased low-level information processing in autism.

Reliability and Validity of a 2-D Video Digitizing System during a Static and a Dynamic Task

Context:The SMART™ software system offers low-cost kinematic analysis through digitization of video from a single camera. The reliability and validity of this product have not been reported.Objective:To assess the reliability and validity of the SMART software during a simple static task and dynamic task.Design:Test–retest to compare assumed neutral and goniometrically measured joint angles in the sagittal plane of the lower extremity.Setting:Research laboratory.Participants:7 in a static task, 16 young, physically active in a dynamic task.Results:Measurement error of the SMART system ranged from 0.29° ± 1.98° to 11.07° ± 1.77°. The interrater reliability (ICC2,1) values ranged from .60 to .92 for the static task and from .76 to .89 for the dynamic task.Conclusions:Based on the results of both studies, the SMART system offers a low-cost alternative for reporting single-plane kinematics during an individual frame of video during static stances and slow dynamic tasks with strong reliability and reasonable validity.

Interaction of Visual and Proprioceptive Feedback During Adaptation of Human Reaching Movements

People tend to make straight and smooth hand movements when reaching for an object. These trajectory features are resistant to perturbation, and both proprioceptive as well as visual feedback may guide the adaptive updating of motor commands enforcing this regularity. How is information from the two senses combined to generate a coherent internal representation of how the arm moves? Here we show that eliminating visual feedback of hand-path deviations from the straight-line reach (constraining visual feedback of motion within a virtual, "visual channel") prevents compensation of initial direction errors induced by perturbations. Because adaptive reduction in direction errors occurred with proprioception alone, proprioceptive and visual information are not combined in this reaching task using a fixed, linear weighting scheme as reported for static tasks not requiring arm motion. A computer model can explain these findings, assuming that proprioceptive estimates of initial limb posture are used to select motor commands for a desired reach and visual feedback of hand-path errors brings proprioceptive estimates into registration with a visuocentric representation of limb position relative to its target. Simulations demonstrate that initial configuration estimation errors lead to movement direction errors as observed experimentally. Registration improves movement accuracy when veridical visual feedback is provided but is not invoked when hand-path errors are eliminated. However, the visual channel did not exclude adjustment of terminal movement features maximizing hand-path smoothness. Thus visual and proprioceptive feedback may be combined in fundamentally different ways during trajectory control and final position regulation of reaching movements.

A Fast and Effective Static Task Scheduling Algorithm in Homogeneous Computing Environments

A Fast and Effective Static Task Scheduling Algorithm in Homogeneous Computing Environments

Interface Dynamics in Cause-Based Partnerships: An Exploration of Emergent Culture

This article examines the behavioral dynamics at the interface between organizations in strategic partnerships called cause-based partnerships (CBPs). These are partnerships between a corporation and one or more nonprofit organizations that address social meta problems such as environmental sustainability or social-justice challenges. Various a priori differences such as tasks, processes, and organizational cultures are expected to affect outcomes, but this article argues that a key determinant of successful CBP performance is behavioral dynamics at the interface between the partners. This article builds a framework for understanding these behavioral dynamics in terms of an emergent culture. Three scenarios—integration, reculturation, and separation—are described for how participants in CBPs continually negotiate a workable set of cultural practices among them-selves. Examples are basedon interviews with CBP managers. These explorations expand the basis for understanding CBP dynamics beyond those provided by static task, process, or common-culture explanations.

Altered quadriceps control in people with anterior cruciate ligament deficiency.

The purpose of this study was to determine whether similar patterns of quadriceps dysfunction are observed when people with anterior cruciate ligament (ACL) deficiency perform static and dynamic tasks. EMG data were collected from 15 subjects with an ACL deficient knee and 15 uninjured subjects as they performed static and dynamic tasks that were isolated to the knee and presented no threat to joint stability. The dynamic task was cyclic flexion and extension in the terminal 30 degrees of knee extension; the static task was an established isometric target-matching protocol. The muscle activity patterns observed during the tasks were evaluated and compared. The subjects with ACL deficiency exhibited quadriceps muscle control strategies that were significantly different from those of the uninjured subjects. This was true in both the dynamic and the static tasks. The findings were most noteworthy in the vastus lateralis muscle. Good agreement (r = -0.73 to -0.75) was observed in subjects' static and dynamic VL results; more moderate agreement was observed in results of the other quadriceps muscles. Diminished quadriceps control was observed when people with ACL deficiency performed static and dynamic tasks. The most striking feature of this impaired control was failure to turn the quadriceps "off" when performing flexion tasks in which the knee extensors are usually "silent." Our findings suggest that quadriceps dyskinesia after ACL injury is relatively global. Changes in neural function and muscle physiology after ACL injury are put forth as the most likely source of the observed dyskinesia.

Utility of using a force and moment wrench to describe hand demand

This study was undertaken to evaluate the utility of using a force and moment wrench to describe the demand on the distal arm tissues and perceived exertion during static gripping tasks. Five right hand dominant university students, who were free of hand or wrist disorders, completed a total of 87 maximum and submaximum gripping tasks. All trials were completed while standing, with the arm adducted and elbow flexed to ninety degrees. The wrist posture was near neutral in all axes during the exertions. Activation levels for muscles of the forearm and hand and rating of perceived exertion were collected. Participants handled objects using 3 grips (cylindrical grip, lateral pinch and pulp pinch) in 8 different ways. The equivalent force and moment wrench for the tasks were also exerted on a modified pinch/grip dynamometer, affixed to a six degree of freedom force cube. This instrumentation allowed the simultaneous collection of the 3 forces, 3 moments and the pinch/grip force about the grip centre. It was expected that the demands of a task and the instrumented task wrench reproduction would be the same, and therefore the slope of the linear regression for the EMG and RPE scatterplots would be equal to one. The RPE slopes ranged from 0.99 (lateral pinch) to 1.11 (cylindrical grip), with R2 greater than 0.89 for all grips. The mean slope for EMG of all muscles ranged from 0.89 (lateral pinch) to 1.38 (pulp pinch), with mean R2 of 0.61 to 0.68. The force and moment wrench system for the categorization of prehension appears to capture the demands on the distal arm tissues and perceived exertion during standardized laboratory holding tasks.

An Adaptive Hybrid Task Partitioning, Scheduling (AHTS), and Load Balancing Strategy for Heterogeneous Distributed System

Heterogeneous Parallel Distributed Processing (PDP) systems, which exploit the aggregate power of a network of workstations (WSs) and Personal Computers (PCs) are an inexpensive alternative to the dedicated parallel supercomputing systems. As these systems are widely available in academic and industrial environments, it is becoming popular to use these computing resources to solve time consuming applications. The main problem with such type of cluster computing environment is the continuous change in the performance of individual WSs/PCs which requires an efficient task partitioning, scheduling, and load balancing to get better performance.In this paper, we investigate the problem of static and runtime tasks allocation for parallel-distributed image computing system. The PDP system has heterogeneity in processors and resources. For such system, we propose an Adaptive Hybrid Task partitioning, Scheduling (AHTS), and load balancing strategy. The investigation is examined on a manager/master and workers model of PDP system. The measured results show that, the AHTS strategy dramatically improves the performance of PDP image computing system and remedy the defects of static and Runtime Task Scheduling (RTS) strategies.

Intramuscular pressure and EMG relate during static contractions but dissociate with movement and fatigue.

Intramuscular pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1). brief static arm abductions at angles from 0 to 90 degrees, with and without 1 kg in the hands; 2). dynamic arm abductions at angular velocities from 9 to 90 degrees /s, with and without 1 kg in the hands; and 3). prolonged static arm abduction at 30 degrees for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions, peak IMP and EMG increased to values higher than those during static contractions, and EMG, but not IMP, increased significantly with speed of abduction. In the nonfatigued supraspinatus muscle, a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery, significant timewise changes of the IMP-to-EMG ratio occurred. The results indicate that IMP should be included along with EMG when mechanical load sharing between muscles is evaluated during dynamic and fatiguing contractions.