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Loes Janssen, Céline Crajé, Matthias Weigelt and Bert Steenbergen

We examined anticipatory motor planning and the interaction among both hands in a discrete bimanual task. To this end, participants had to grasp and manipulate two cylindrical objects simultaneously under varying conditions in which (a) the grip selection requirements, i.e., orientation of the to-be-grasped objects, differed between the two hands and (b) the type of grip for one hand was preinstructed, while the grip for the other hand was free choice. Results showed that participants, when grasping for two bars with a free grip choice, prioritized planning for comfortable end postures over symmetry of movement execution. Furthermore, when participants were free to choose a grip for their left hand, but were instructed on how to grasp an object with their right hand, we found no interaction between the grip selections of both hands, suggesting that motor planning proceeds independently for both hands.

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Ran Zheng, Ilana D. Naiman, Jessica Skultety, Steven R. Passmore, Jim Lyons and Cheryl M. Glazebrook

movements due to cognitive processing (i.e., time for movement organization) or motor processing (i.e., time for force generation). Movement Execution Unlike motor planning, there is a discrepancy in the literature with respect to whether or not movement execution is different in the ASD population

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Louisa D. Raisbeck, Jed A. Diekfuss, Dustin R. Grooms and Randy Schmitz

in the primary motor cortex, somatosensory cortex, and insular region of the left hemisphere. The authors surmised from these regions that are associated with sensory function, that an external focus promoted task-adequate brain activity for movement execution by shifting focus toward exteroceptive

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Michael J. Hiley and Maurice R. Yeadon

The upstart is a fundamental skill in gymnastics, requiring whole body coordination to transfer the gymnast from a swing beneath the bar to a support position above the bar. The aim of this study was to determine the solution space within which a gymnast could successfully perform an upstart. A previous study had shown that the underlying control strategy for the upstart could be accounted for by maximizing the likelihood of success while operating in a noisy environment.1 In the current study, data were collected on a senior gymnast and a computer simulation model of a gymnast and bar was used to determine the solution space for maximizing success while operating in a noisy environment. The effects of timing important actions, gymnast strength, and movement execution noise on the success of the upstart were then systematically determined. The solution space for the senior gymnast was relatively large. Decreasing strength and increasing movement execution noise reduced the size of the solution space. A weaker gymnast would have to use a different technique than that used by the senior gymnast to produce an acceptable success rate.

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M.J.M. Volman

The effect of amplitude incongruence (small circles–large circles) and form incongruence (circles–lines) on the performance of the affected and non-affected arm was examined in 12 children with hemiplegic cerebral palsy in bimanual rhythmic drawing tasks. Amplitude and form incongruence are assumed to be associated with aspects of movement execution and movement planning, respectively. The following questions were addressed: Does amplitude or form incongruence in bimanual coordination result in: (a) accommodation of the affected or non-affected arm, or both, (b) an increase of temporal variability of drawing movements of the affected or non-affected arm, and (c) a decrease of bimanual coordination stability? Form incongruence resulted in accommodation of both affected and non-affected arm in a similar way found in non-disabled participants. Despite this accommodation, the temporal variability of both affected and non-affected arm was increased, and coordination stability decreased, because the spatial trajectories of affected and non-affected arm were still rather dissimilar. Amplitude incongruence resulted in accommodation of either the affected arm (large circles required) or non-affected arm (small circles required), and in an increase or decrease of temporal variability of the affected arm, depending on the degree of spatial similarity of the trajectories of affected and non-affected arm. These findings suggest that in children with hemiplegic cerebral palsy aspects of movement execution, but not aspects of movement planning are affected by the “hemiplegic” condition.

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Andrew M. Johnson, Philip A. Vernon, Quincy J. Almeida, Linda L. Grantier and Mandar S. Jog

The effect of a precue on improving movement initiation (i.e., reaction time; RT) is well understood, whereas its influence on movement execution (i.e., movement time; MT) has rarely been examined. The current study investigated the influence of a directional precue (i.e., left vs. right) on the RT and MT of simple and discrete bi-directional movements in a large sample of Parkinson's disease patients and healthy control participants. Both patients and controls were tested twice, with testing sessions separated by 2 hours. Patients were tested first following an overnight levodopa withdrawal and again after they had taken their medication. Both patients and controls demonstrated a significant RT improvement when information was provided in advance. MT in both healthy participants and medicated patients was, however, slower with the provision of advance information, while unmedicated patients showed no significant MT effects. These results suggest that while the basal ganglia may not be involved in motor program selection, they may dynamically modulate movement execution.

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Aaron England, Timothy Brusseau, Ryan Burns, Dirk Koester, Maria Newton, Matthew Thiese and Benjamin Chase

In adult performers, research suggests that mental representations (MRs) mediate performance of skilled movement. During adolescence, cortical brain areas responsible for generating MRs develop rapidly along with limb size, which, together, may affect movement and movement representations. The aim of this study was to examine the relationship between adolescent MRs and free-throw shooting expertise. Using structural dimensional analysis of MRs, skilled (n = 11) and less skilled (n = 11) participants sorted free-throw submovements according to their relatedness in movement execution. Data were analyzed using a hierarchical cluster analysis, factor analysis, and invariance test to examine between-group cluster comparisons. Cluster solutions for the skilled and less skilled participants were significantly variant (λ = 0.56). This method of measuring MRs distinguished expertise-related differences in MRs in an adolescent population. Findings may influence methods in which practitioners detect motor-planning faults, track development, and provide feedback to trainees.

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Veena Iyengar, Marcio J. Santos and Alexander S. Aruin

We investigated whether slower velocity of arm movement affects grip-force generation in conditions with the finger touch provided to the wrist of the target arm. Nine subjects performed the task of lifting and transporting an object at slow, intermediate, and fast velocities with a light finger touch from the contralateral arm and without it. There was an effect of velocity of arm movement on grip-force generation in both conditions. However, when the no touch and touch trials performed with similar velocity were matched, the effect of touch on grip-force reduction was statistically significant (p < .001). The observed decrease in grip force could not be explained by slower movement execution in the touch conditions and underlines the importance of using a contralateral touch in the performance of activities of daily living. It also points to a possibility of the development of therapeutic advances for the enhancement of grip-force control in patients with neurological impairments.

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Gavin P. Lawrence, Michael A. Khan, Stuart Mourton and Pierre-Michel Bernier

The objective of the current study was to determine whether the reliance on visual feedback that develops with practice is to due utilizing vision to adjust trajectories during movement execution (i.e., online) and/or to enhance the programming of subsequent trials (i.e., offline). Participants performed a directional aiming task with either vision during the movement, dynamic feedback of the trajectory of the movement or the movement endpoint. The full vision condition was more accurate during practice than the other feedback conditions but suffered a greater decrement in performance when feedback was removed. In addition, the reliance on trajectory feedback was greater compared with the endpoint feedback. It appears that the reliance on visual feedback that develops with practice was due to both online and offline processing.

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Zong-Ming Li

Mechanical degrees of freedom (DOF) are defined as the minimum number of independent coordinates needed to describe a system’s position. The human musculoskeletal system has many mechanical DOF through which countless movements are accomplished. In the motor control field, one of the aspirations is to understand how the many DOF are organized for movement execution—the so-called DOF problem. Natural movements are characterized by the coordination of the DOF such that few vary independently. The concept of functional degrees of freedom (fDOF) is introduced to describe the very limited DOF of purposeful, coordinated movements. Deterministic (i.e., constraint satisfaction) and statistical (i.e., principal component analysis) approaches are used to determine fDOF. In contrast to DOF as a mechanical descriptor, fDOF emphasizes the mechanisms of human movements and corroborates our search for the solution to the DOF problem.