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Stacy M. Lopresti-Goodman, Michael J. Richardson, Reuben M. Baron, Claudia Carello and Kerry L. Marsh

The actualization of a simple affordance task—grasping and moving wooden planks of different sizes using either one or two hands—was assessed in the context of taskrelevant (plank sequence, plank presentation speed) and task-irrelevant (cognitive load) manipulations. In Experiment 1, fast (3 s/plank) and self-paced (≈5 s/plank) presentation speeds revealed hysteresis; the transition point for ascending series was greater than the transition point for descending series. Hysteresis was eliminated in the slowest presentation speed (10 s/plank). In Experiment 2, hysteresis was exaggerated by a cognitive load (counting backward by seven) for both fast and slow presentation speeds. These results suggest that behavioral responses to the attractor dynamics of perceived affordances are processes that require minimal cognitive resources.

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Ana F. Silva, Pedro Figueiredo, Sara Morais, João P. Vilas-Boas, Ricardo J. Fernandes and Ludovic Seifert

 years (after the peak high velocity; Malina, Bouchard, & Bar-Or, 2004 ). The main aim of the current study was to examine young swimmers’ behavioral flexibility (through upper-limb coordination patterns) when task constraints (swimming speed and stroke frequency) are manipulated, investigating the

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Geetanjali Gera, Sandra Freitas, Mark Latash, Katherine Monahan, Gregor Schöner and John Scholz

This study investigated the use of motor abundance during the transport and placing of objects that required either precise or minimal orientation to the target. Analyses across repetitions of the structure of joint configuration variance relative to the position and orientation constraints were performed using the Uncontrolled Manifold (UCM) approach. Results indicated that the orientation constraint did not affect stability of the hand’s spatial path. Orientation was weakly stabilized during the late transport phase independent of the orientation constraint, indicating no default synergy stabilizing orientation. Stabilization of orientation for conditions most requiring it for successful insertion of the object was present primarily during the adjustment phase. The results support the hypothesis that a major advantage of a control scheme that utilizes motor abundance is the ability to resolve multiple task constraints simultaneously without undue interference among them.

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Jill Whitall, Larry Forrester and Nancy Getchell

The present study examined the effect of nonspecific task constraints on the multilimb coordination task of preferred-speed crawling. Adult subjects undertook three trials each of the following randomly ordered conditions: forward prone (FP), backward supine (BS), backward prone (BP) and forward supine (FS). Subjects adopted specific coordinative solutions consistent with task-related function rather than anatomical specification. The patterns were relatively stable, with BP being least stable. Across conditions, subjects changed their velocity in a predictable order that corresponded to the various constraints. These velocity changes were largely attributable to stride length adjustments and not limb frequency. Within a condition, neither velocity nor anthropometrics appeared to influence the coordinative solution. Overall, rather large differences were found in coordinative solutions, possibly owing to the nature of the tasks and/or individual searching strategies. The results were interpretable within a dynamic approach to coordination and support the idea that coordination is functionally rather than anatomically determined.

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Larry Forrester and Jill Whitall

The effects of directional and postural constraints on preferred speed quadrupedal gait patterns were studied by comparing responses to four hand-foot crawling tasks: forward and backward prone (FP and BP) and forward and backward supine (FS and BS). A central question was whether the task dynamics evident at the end-effector level also appear at the joint effector system level. Timing of reversals in each limb's proximal effector system joints was shown to be related to the functional role (propulsion or reaching) of the limb. Within joints, task constraint changes strongly tended to affect reversal times, and time-reversed directional comparisons tended to show “mirroring” responses. Peak reaching positions were also closely associated with forelimb touchdowns and interlimb coordination. Discussion centers on task function, task dynamics, and their influence on effector system behavior.

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Gonçalo Dias, Micael S. Couceiro, João Barreiros, Filipe M. Clemente, Rui Mendes and Fernando M.L. Martins

The main objective of this study is to understand the adaptation to external constraints and the effects of variability in a golf putting task. We describe the adaptation of relevant variables of golf putting to the distance to the hole and to the addition of a slope. The sample consisted of 10 adult male (33.80 ± 11.89 years), volunteers, right handed and highly skilled golfers with an average handicap of 10.82. Each player performed 30 putts at distances of 2, 3 and 4 meters (90 trials in Condition 1). The participants also performed 90 trials, at the same distances, with a constraint imposed by a slope (Condition 2). The results indicate that the players change some parameters to adjust to the task constraints, namely the duration of the backswing phase, the speed of the club head and the acceleration at the moment of impact with the ball. The effects of different golf putting distances in the no-slope condition on different kinematic variables suggest a linear adjustment to distance variation that was not observed when in the slope condition.

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Frederik J.A. Deconinck, Dirk De Clercq, Geert J.P. Savelsbergh, Rudy Van Coster, Ann Oostra, Griet Dewitte and Matthieu Lenoir

One-handed catching behavior was studied in nine 6- to 8-year-old boys with Developmental Coordination Disorder (DCD) and nine matched typically developing boys. The participants performed a catching task under two conditions. In the first condition, one ball speed was used while three ball speeds were randomly presented in the second condition. Boys with DCD showed a significantly smaller maximal hand aperture and a lower maximal closing velocity in both the first and the second condition; however, the temporal structure of the catch as well as the adaptations to the varying ball speeds did not differ between groups. This leads to the suggestion that the motor problems of boys with DCD in one-handed catching are not primarily due to debilitated visuo-perceptual or planning processes but are more likely caused by problems at the execution level.

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Anderson Nascimento Guimarães, Herbert Ugrinowitsch, Juliana Bayeux Dascal, Alessandra Beggiato Porto and Victor Hugo Alves Okazaki

in the range of motion during the practice and developed a pattern of control adapted to the environment and task constraints. CC = cross correlation; AAG = angle–angle graphic; PPG = position–position graphic; PTG = position–time graphic, JROM = joint range of motion; PRAV = pick range of angular

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Joanne Smith, Madeleine Grealy and Gert-Jan Pepping

We investigated a general theory accounting for the guidance of ongoing movements in an interceptive reaching task. The aim was to assess the premise of tau-coupling that the coupling constant k, the ratio of taus (τs) of motion gaps between hand and object, reflects the kinematics of the on-going movement. The spatial and temporal constraints of the interceptive action were manipulated in three task conditions. While the time dependent counterpart of k, K(t) exhibited task effects, k itself could not distinguish between task manipulations. K(t) showed large variability during the initial acceleration phase, small variability during the rest of the movement, and task dependent changes during the final deceleration phase of interception. The findings highlight the importance of clarifying what constitutes as t-coupling.

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Graham E. Caldwell and Li Li

In this commentary we question whether the relationship between muscle activity and joint moments is the same for natural motor tasks as for controlled experimental situations. An important consideration in this regard is the identification of the correct electromechanical delay (EMD) for comparing EMG and joint moment data. Data from recent cycling studies are used to illustrate the importance of EMD, and how changing task constraints can alter the relation between muscle activity and joint moment balance for bi-articular antagonist pairs.