Search

This paper examines the influence of task and skill level constraints on the generality of proximal-distal control for within-limb movement coordination. Analysis and synthesis of the experimental findings leads to the proposition that proximal-distal is one of several within-limb patterns of coordination, including: the reverse distal-proximal sequence, simultaneous activation of segments, and other sequence variations of this. The probability of particular patterns occurring is induced by task constraints and skill level of the individual, together with their evolving biomechanical consequences, including: open/closed chain, absorption/propulsion of force, magnitude of momentum, and accuracy/timing. We develop the theoretical perspective that classes of task constraints induce particular types of neuromechanical organization to within-arm or within-leg segment coordination. In this task constraint framework, proximal-distal within-limb organization is a particular rather than a general case for within-limb coordination. The limitations of anatomically-based accounts of directional change for within-limb organization are discussed with reference to a general functional degrees of freedom task constraint framework for movement coordination and control.

The present study investigated the transversal rotation of body and its relation to the horizontal movement for expert shooters and novices in a pistol aiming task. Participants stood on a force plate with an air pistol and aimed it to the centre of a target, positioned 1.4 m above the floor and 10 m away from the force plate, for 30 s as accurately as possible. The results revealed that the novice group showed greater transversal body variability represented by the free moment (FM) than the expert group. Correlation analysis showed that there is tight coupling between the FM and centre of pressure both in the anterior–posterior and medio-lateral directions for the expert group while only strong coupling of that in the anterior–posterior direction for the novice group. The findings suggest that FM is a critical factor to accurately aim the pistol on the target and there is a different postural strategy, in terms of the body motion in the transversal and horizontal space, as a function of skill level to realise success in the pistol aiming task. [ABSTRACT FROM AUTHOR]

The experiment reported was designed to investigate the interaction of information and force variability on the evolving search strategy, specifically testing the hypothesis of convergence to tolerant regions. Participants were required to produce proportional bimanual isometric force output over three days of practice, with no prespecified force target and where performance was more tolerant to force variability at higher forces. The duration of intermittent visual feedback was manipulated to test the effects of information and force variability on the search process and the resulting sensitivity to tolerant regions of the task space. The findings showed that just under half of the participants exploited more tolerant regions and that this was predicted by the initial force conditions. Different characterizations of the individual search patterns were also predicted by inherent force-dependent variability and initial force conditions. Visual intermittency feedback did not affect the time-dependent properties of the search process but did influence the within-trial variability. Our findings suggest that the attraction to tolerant regions needs to be considered within the interactions of the different categories of constraints on the search process. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated perception and action coupling as reflected in a mapping between time-to-contact (TTC) and time-to-peak-velocity (TPV) for children and youths aged 7 to 8, 11 to 12, and 15 to 16 years old and adults aged 19 to 20 years old performing a task that allowed the participants to self-select the interception position in a baseball-like batting game on a graphics tablet. Method: The moving object to be hit for distance had curvilinear trajectories toward the hitter that were determined by simulated weightings of gravity and velocity. Results: Successful interceptions in all age groups were characterized by a mapping of mean TTC and TPV and a higher correlation of these variables with increasing age. The object was hit at approximately 90% TPV so that the implement was still accelerating on contact--an adaptive task feature for a striking distance criterion. Conclusion: The results are consistent with theories of perception--action coupling that are congruent with the ecological and dynamical approaches to action where TTC, a source of environmental information, is mapped relative to TPV, largely independent of the particular kinematic task demands of the approaching object. The organization of the coupling of TTC prior to TPV was evident across all age groups and is evidence for a common strategy for this type of interceptive action. The age-related changes in the strength of the relationship between TTC and TPV are evidence of increased sensitivity to the coupling between TTC and TPV.

Purpose: This study investigated the age-related speed--accuracy strategies of children, adolescents, and adults in performing a rapid striking task that allowed the self-selection of the interception position in a virtual, two-dimensional environment. Method: The moving target had curvilinear trajectories that were determined by combinations of simulated weightings of gravity and velocity. Mass and coefficient of restitution were also assigned to the target to encourage interception with maximal effector velocity. The performance outcome was the measure of the distance that the target traveled following interception that was the result of the effector velocity and angle of motion at the time that the target was struck. Results: The number of accurate interceptions increased linearly with age. Younger children hit the object at a slower velocity and had longer response latency and movement times compared with older age groups. Effector velocity at contact was shown to be parabolic and reached an asymptote for older children and adolescents followed by a decrease in effector velocity at contact among the adults, although horizontal effector displacement increased linearly with age. Conclusions: The increased effector displacement and the asymptotic/parabolic trend for effector velocity at contact with age reveals an age-related speed--accuracy trade-off in this interception task. The age limitations appear more related to the reduced capacity to predict the spatial-temporal properties of the target trajectory than do age-related limitations in the speed of information processing. (Contains 6 figures and 7 tables.)