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David Antonio Gonzalez, Adam Dubrowski and Heather Carnahan

Visual and haptic integration has been examined extensively, however little is known about alternative premovement sensory information to help in the anticipatory control of prehension. This study explored the concept of using auditory cues as an alternative premovement cue. Individuals lifted champagne flutes filled with various levels of water; and one group was given a sound cue before lifting. Sounds provided a precue regarding fluid level and hence mass. Results showed that auditory cues were used to predict the “target force” required to lift the masses, as evidenced by scaling of grip rates as a function of mass in the auditory cue group only. It was hypothesized that individuals used the auditory cues to preprogram the grasping forces produced during the lifting movement.

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Peter D. Neilson

This commentary firstly supports Smeets and Brenner in their choice of a kinematic trajectory, submitting that the challenge posed by the rival torque-change formulation is resolved by consideration of intermittency in human movement control. Second, it examines the choice of optimization criterion for trajectory planning, arguing in favor of minimum acceleration rather than minimum jerk. Third, using the notion of optimized trajectories in task-dependent coordinate space together with synergy generation, it suggests a formulation that reduces the processing load entailed in Smeets and Brenner's proposal of individual trajectories for each digit.

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Jinsung Wang and George E. Stelmach

Smeets and Brenner propose a model that attempts to account for the action patterns involved in prehensile behaviors. However, the model does not provide a full account of the available data on temporal and spatial relationships between the transport and grasp components. Predictions from the model in its current form appear to correspond only to experimental results in a very general way.

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Ronald G. Marteniuk and Christopher P. Bertram

Smeets and Brenner have suggested that it may be time to abandon Jeannerod’s “classical approach” to studying human prehension, and have presented a mathematical model as an alternative. We argue that this model provides insufficient grounds for widespread acceptance, and question whether or not such an approach furthers the science of motor control.

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Laurent Vigouroux, Mathieu Domalain and Eric Berton

The objective of this study was to identify the impact of modifying the object width on muscle and joint forces while gripping objects. The experimental protocol consisted to maintain horizontally five objects of different widths (3.5, 4.5, 5.5, 6.5, and 7.5 cm) with a thumb–index finger grip. Subjects were required to grasp spontaneously the object without any instruction regarding the grip force (GF) to apply. A biomechanical model of thumb–index finger pinch was developed to estimate muscle and joint forces. This model included electromyography, fingertip force, and kinematics data as inputs. The finger joint postures and the GF varied across the object widths. The estimated muscle forces also varied significantly according to the object width. Interestingly, we observed that the muscle force/GF ratios of major flexor muscles remain particularly stable with respect to the width whereas other muscle ratios differed largely. This may argue for a control strategy in which the actions of flexors were preserved in spite of change in joint postures. The estimated joint forces tended to increase with object width and increased in the distal–proximal sense. Overall, these results are of importance for the ergonomic design of handheld objects and for clinical applications.

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Josje van Houwelingen, Sander Schreven, Jeroen B.J. Smeets, Herman J.H. Clercx and Peter J. Beek

In this paper, a literature review is presented regarding the hydrodynamic effects of different hand and arm movements during swimming with the aim to identify lacunae in current methods and knowledge, and to distil practical guidelines for coaches and swimmers seeking to increase swimming speed. Experimental and numerical studies are discussed, examining the effects of hand orientation, thumb position, finger spread, sculling movements, and hand accelerations during swimming, as well as unsteady properties of vortices due to changes in hand orientation. Collectively, the findings indicate that swimming speed may be increased by avoiding excessive sculling movements and by spreading the fingers slightly. In addition, it appears that accelerating the hands rather than moving them at constant speed may be beneficial, and that (in front crawl swimming) the thumb should be abducted during entry, catch, and upsweep, and adducted during the pull phase. Further experimental and numerical research is required to confirm these suggestions and to elucidate their hydrodynamic underpinnings and identify optimal propulsion techniques. To this end, it is necessary that the dynamical motion and resulting unsteady effects are accounted for, and that flow visualization techniques, force measurements, and simulations are combined in studying those effects.

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Allen W. Burton, Nancy L. Greer and Diane M. Wiese-Bjornstal

This study examined the effect of ball size on the movement patterns used by children and adults to grasp a ball and then to throw it as hard as possible. A total of 104 kindergarten, second-grade, fourth-grade, eighth-grade, and young adult males and females were asked to pick up six styrofoam balls of different diameters (from 4.8 to 29.5 cm) four times each as they were presented in random order, and then throw them as hard as possible at a wall 6.7 m away. Transitions from one- to two-hand grasps were made as ball diameters increased, with older subjects switching at significantly larger diameters than younger subjects (p<.0001); however, when ball size was scaled to hand size, older subjects switched at significantly smaller relative diameters than younger subjects (p<.Ol), indicating that hand size may be a critical factor in determining grasp form. Transitions from one- to two-hand throws were made by less than 25% of the subjects (mostly kindergartners and females), demonstrating a strong preference by older children and adults for throwing with one hand, even with ball diameters larger than a subject’s hand size.

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Sara M. Scharoun, David A. Gonzalez, Eric A. Roy and Pamela J. Bryden

Grasping an object seems simple. However, fine-tuned cognitive and sensorimotor processes underlie grasping and other goal-directed actions performed in everyday life. Examining these processes has important implications for understanding the rate at which motor control is developing and declining

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Grace C. Bellinger, Kristen A. Pickett and Andrea H. Mason

grasping. The reaching or transport component requires a person to take his or her hand from an initial position and place it in space so that it contacts the target at a velocity that facilitates the grasping component. The grasping portion involves orienting, shaping, and then closing the hand to