Exchange‐based communication training may not consistently facilitate communication in the absence of the requested item

The role of stimulus presence on spontaneous communication was assessed with 3 participants in a nonconcurrent multiple baseline with embedded reversals design. Participants were taught to request 2 highly preferred items. Once mastery criterion was met, test sessions were conducted with stimuli either visible or absent from the room, and request rate was measured. For 2 participants, training produced requests in both the presence and absence of the stimulus. For one participant, however, the presence of the stimulus was necessary to evoke the response. Results suggest that teaching individuals to request items when they are present may not consistently lead to requests when those items are absent.     

Examining the Spatiotemporal Disruption to Gaze When Using a Myoelectric Prosthetic Hand

The aim of this study was to provide a detailed account of the spatial and temporal disruptions to eye-hand coordination when using a prosthetic hand during a sequential fine motor skill. Twenty-one able-bodied participants performed 15 trials of the picking up coins task derived from the Southampton Hand Assessment Procedure with their anatomic hand and with a prosthesis simulator while wearing eye-tracking equipment. Gaze behavior results revealed that when using the prosthesis, performance detriments were accompanied by significantly greater hand-focused gaze and a significantly longer time to disengage gaze from manipulations to plan upcoming movements. The study findings highlight key metrics that distinguish disruptions to eye-hand coordination that may have implications for the training of prosthesis use.     

An examination of lower limb asymmetry in ankle isometric force control

While asymmetries have been observed between the dominant and non-dominant legs, it is unclear whether they have different abilities in isometric force control (IFC). The purpose of this study was to compare ankle IFC between the legs. IFC is important for stabilization rather than object manipulation, and people typically use their non-dominant leg for stabilization tasks. Additionally, studies suggested that a limb can better acquire a motor task when the control mechanism of the task is related to what the limb is specialized for. We hypothesized that the non-dominant leg would better (1) control ankle IFC with speed and accuracy, and (2) acquire an ankle IFC skill through direct learning and transfer of learning. Two participant groups practiced an IFC task using either their dominant or non-dominant ankle. In a virtual environment, subjects moved a cursor to hit 24 targets in a maze by adjusting the direction and magnitude of ankle isometric force with speed (measured by the time required to hit all targets or movement time) and accuracy (number of collisions to a maze wall). Both groups demonstrated similar movement time and accuracy between the dominant and non-dominant limbs before practicing the task. After practice, both groups showed improvement in both variables on both the practiced and non-practiced sides (p < .01), but no between-group difference was detected in the degree of improvement on each side. The ability to control and acquire the IFC skill was similar between the legs, which did not support the brain is lateralized for ankle IFC.     

Impact of Tactile Sensation on Dexterity: A Cross-Sectional Study of Patients With Impaired Hand Function After Stroke

The authors sought to explore the impact of tactile sensation on manual dexterity and the validity of the strength-dexterity test in subjects with chronic impairments after stroke in a cross-sectional study of 24 patients with impaired hand function after stroke. Dexterity was assessed by the strength-dexterity test, Box and Blocks, and Nine-Hole Peg Test, and the ABILHAND questionnaire. Sensation was measured by pinprick, cotton-wool, graphesthesia, and 2-point discrimination tests. Sensation in the paretic hand had strong association with paretic hand performance in the strength-dexterity test and Nine-Hole Peg Test and explained 13% of the variance. Sensation in the nonparetic hand was associated with the results of the ABILHAND questionnaire. Among sensory tests, 2-point discrimination had the strongest association with dexterity tests. No significant correlations between sensation, pinch force, and dexterity tests were found for the nonparetic hand. The strength-dexterity test exhibited strong correlations with the other dexterity measures and with pinch force. There is an association between tactile sensation and dexterous performance in the paretic hand; activity level performance is associated with sensation in the nonparetic hand. The study supports the validity of the strength-dexterity test when applied in subjects in the chronic stage after stroke.     

Force and Directional Force Modulation Effects on Accuracy and Variability in Low-Level Pinch Force Tracking

The authors investigated how varying the required low-level forces and the direction of force change affect accuracy and variability of force production in a cyclic isometric pinch force tracking task. Eighteen healthy right-handed adult volunteers performed the tracking task over 3 different force ranges. Root mean square error and coefficient of variation were higher at lower force levels and during minimum reversals compared with maximum reversals. Overall, the thumb showed greater root mean square error and coefficient of variation scores than did the index finger during maximum reversals, but not during minimum reversals. The observed impaired performance during minimum reversals might originate from history-dependent mechanisms of force production and highly coupled 2-digit performance.     

No Relationship Between Joint Position Sense and Force Sense at the Shoulder

In practice, a single test is used to quantify an individual's proprioception. Previous studies have not found a correlation between joint position sense (JPS) and force sense (FS), which are submodalities of proprioception. The purpose of the present study is to determine if root mean square (RMS) error in JPS and FS are related at the shoulder, controlling for external load and elevation angle. Active shoulder angle and force reproduction protocols were performed. No correlation was found between JPS and FS (r = –.019, p = .941) nor were any individual angle and load combinations significant. The main effect for angle in JPS was significant (p < .001). Follow-up contrast demonstrated a significant (p < .001) decrease in RMS error with increased elevation. A significant load by angle interaction was found for FS (p = .014). Follow-up simple effects tests by angle demonstrated RMS error decreased with load at 50° and 70° but not at 90°. By load, RMS error only decreased for 120% between 50° and 90°. JPS and FS demonstrate different behavior with load and angle. This differing behavior is more likely responsible for the lack of correlation than angle and load differences in JPS and FS protocols.     

Motor imagery ability and internal representation of movement in children with probable developmental coordination disorder

It has been hypothesised that deficits in the functioning of the mirror neuron system (MNS) and internal modelling may contribute to the motor impairments associated with DCD. These processes can be explored behaviourally through motor imagery paradigms. Motor imagery proficiency of children with and without probable DCD (pDCD) was examined using a complex hand rotation task to explore whether motor imagery strategies could be used during more complex tasks. Forty-four boys aged 7–13 years participated, 22 with pDCD (mean = 9.90 years ± 1.57) and 22 controls (mean = 9.68 years ± 1.53). Participants completed the task twice: with and without motor imagery instructions. Stimuli were presented in two rotational axes – palm/back, and eight 45° rotational steps. Both groups showed evidence of following the biomechanical and postural constraints of actual movements. Responses of children with pDCD were slower and less accurate than controls, with group differences increasing alongside task complexity. A greater impact of biomechanical constraints for accuracy was observed in the DCD group. The response characteristics of children with pDCD likely reflects a reduced capacity to mentally manipulate a body schema and reduced visuo-motor processing capabilities. Behaviourally, these processes are linked to MNS and internal modelling function, suggesting deficits in these systems may contribute to the movement difficulties characteristic of DCD.     

A unified approach for revealing multiple balance recovery strategies

In human balance recovery, different strategies have been proposed with generally overlooked knee motions but extensive focus on the ankle, hip, and step strategies. It is not well understood whether maintaining balance is regulated at the lower “muscular–articular” level of coordinating segment joints or at a higher level of controlling whole body dynamics. Whether balance control is to minimize joint degrees of freedom (DOF) or utilize all the available DOF also remains unclear. This study aimed to use a realistic musculoskeletal human model to identify multiple balance recovery strategies with a single optimization criterion. Movements were driven by neural excitations (which activated muscle force generation) and were assumed to be symmetric. Balance recoveries were simulated with forward-inclined straight body postures as the initial conditions. When the position of the toes was fixed, balance was regained with virtually straight knees and mixed ankle/hip strategies. Under a severely perturbed condition, use of the forward hop strategy after releasing the fixed-toes constraint indicated spontaneous recruitment or suppression of DOF, which mimicked functions of optimally computed CNS commands in humans. The results also indicated that increase/decrease in the number of DOF depends on the imposed perturbation intensity and movement constraints.     

Reprint of “Co-occurring motor,language and emotional–behavioral problems in children 3–6 years of age”

PurposeDevelopmental Coordination Disorder (DCD) has been shown to co-occur with behavioral and language problems in school-aged children, but little is known as to when these problems begin to emerge, or if they are inherent in children with DCD. The purpose of this study was to determine if deficits in language and emotional–behavioral problems are apparent in preschool-aged children with movement difficulties.MethodTwo hundred and fourteen children (mean age 4 years 11 months, SD 9.8 months, 103 male) performed the Movement Assessment Battery for Children 2nd Edition (MABC-2). Children falling at or below the 16th percentile were classified as being at risk for movement difficulties (MD risk). Auditory comprehension and expressive communication were examined using the Preschool Language Scales 4th Edition (PLS-4). Parent-reported emotional and behavioral problems were assessed using the Child Behavior Checklist (CBCL).ResultsPreschool children with diminished motor coordination (n = 37) were found to have lower language scores, higher externalizing behaviors in the form of increased aggression, as well as increased withdrawn and other behavior symptoms compared with their typically developing peers.ConclusionsMotor coordination, language and emotional–behavioral difficulties tend to co-occur in young children aged 3–6 years. These results highlight the need for early intervention.     

Muscle force compensation among synergistic muscles after fatigue of a single muscle

PurposeThe aim of this study was to examine control strategies among synergistic muscles after fatigue of a single muscle. It was hypothesized that the compensating mechanism is specific for each fatigued muscle.MethodsThe soleus (SOL), gastrocnemius lateralis (GL) and medialis (GM) were fatigued in separate sessions on different days. In each experiment, subjects (n = 11) performed maximal voluntary contractions prior to and after fatiguing a single muscle (SOL, GL or GM) while the voluntary muscle activity and torque were measured. Additionally, the maximal single twitch torque of the plantarflexors and the maximal spinal reflex activity (H-reflex) of the SOL, GL and GM were determined. Fatigue was evoked using neuromuscular stimulation.ResultsFollowing fatigue the single twitch torque decreased by −20.1%, −19.5%, and −23.0% when the SOL, GL, or GM, have been fatigued. The maximal voluntary torque did not decrease in any session but the synergistic voluntary muscle activity increased significantly. Moreover, we found no alterations in spinal reflex activity.ConclusionsIt is concluded that synergistic muscles compensate each other. Furthermore, it seems that self-compensating mechanism of the fatigued muscles occurred additionally. The force compensation does not depend on the function of the fatigued muscle.