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Karl M. Newell

can be made for standing, walking, running, and certain forms of object-interaction (prehension—reaching and grasping) to be the fundamental motor skills. They are fundamental not only because they are the basis of human movement in distinct classifications of action functions but also because they

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Jay L. Alberts, Christopher M. Elder, Michael S. Okun and Jerrold L. Vitek

The aim of this study was to determine the effects of unilateral deep brain stimulation (DBS) on the control and coordination of grasping forces produced by Parkinson's disease (PD) patients. Ten advanced PD patients with unilateral DBS in the globus pallidus (GPi) or the subthalamic nucleus (STN) (5 patients in each group) performed a functional bimanual dexterous manipulation task. Experiments were performed in the “Off” medication state with DBS “On” and “Off.” DBS resulted in (a) significant clinical improvements, (b) greater maximum grip force for both limbs, (c) reduced movement time, and (d) bilateral coupling of grasping forces. There were no significant differences between the GPi and STN groups for any clinical or kinematic measures. DBS of the GPi and STN leads to an improvement in the motor functioning of advanced PD patients. Improvement in force-timing specification during DBS might allow PD patients to employ a feedforward method of force control.

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Stella Maris Michaelsen, Eliane C. Magdalon and Mindy F. Levin

Decreased dexterity in chronic stroke survivors results in diminished hand use and impacts quality of life. We studied reach-and-grasp coordination and aperture scaling during reach to grasp using different grasp types and object sizes (33–55mm). Chronic stroke survivors with hand paresis and controls grasped cylinders with the whole hand or fingertips. Three stroke subjects with more severe hand paresis had disrupted reach/grasp coordination and used compensatory strategies for arm transport and/or grasping. Nine stroke subjects with less severe paresis scaled aperture to cylinder diameter (p < .001) but had slower movements, used excessive trunk movement, and had prolonged deceleration times. Relative time to maximal grip aperture (TMA) occurred earlier in stroke subjects and in both groups when grasping the small cylinder (p < .002). Despite deficits in reach and grasp, chronic stroke survivors with mild to moderate hand paresis may retain grip aperture scaling to object size for different grasp types.

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Sydney Y. Schaefer, Stacey L. DeJong, Kendra M. Cherry and Catherine E. Lang

This study investigated whether grip type and/or task goal influenced reaching and grasping performance in poststroke hemiparesis. Sixteen adults with poststroke hemiparesis and twelve healthy adults reached to and grasped a cylindrical object using one of two grip types (3-finger or palmar) to achieve one of two task goals (hold or lift). Performance of the stroke group was characteristic of hemiparetic limb movement during reach-to-grasp, with more curved handpaths and slower velocities compared with the control group. These effects were present regardless of grip type or task goal. Other measures of reaching (reach time and reach velocity at object contact) and grasping (peak thumb-index finger aperture during the reach and peak grip force during the grasp) were differentially affected by grip type, task goal, or both, despite the presence of hemiparesis, providing new evidence that changes in motor patterns after stroke may occur to compensate for stroke-related motor impairment.

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Hilde Van Waelvelde, Willy De Weerdt, Paul De Cock, Bouwien C.M. Smits-Engelsman and Wim Peersman

The aim of this study was to compare the quality of ball catching performance of children with DCD to the performance of younger typically developing children. The outcome measures used were a modified ball catching item of the Test of Gross Motor Development and the number of grasping errors in a ball catching test. In the study, children with DCD were matched with younger typically developing children according to gender and the number of caught balls in the ball catching test. Children with DCD made significantly more grasping errors and scored significantly lower on the modified TGMD-item. Children with DCD were not only delayed in ball catching but they also seemed to use different movement strategies compared to younger typically developing children.

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Bernstein's Heritage The Active Search for Information: From Reflexes to the Model of the Future (1966) Losif M. Feigenberg * Onno G. Meijer * 7 1999 3 3 225 236 10.1123/mcj.3.3.225 Original Research A New View on Grasping Jeroen B.J. Smeets * Eli Brenner * 7 1999 3 3 237 271 10.1123/mcj.3

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Edwin M. Robertson

The concept of canonical representations within the motor system has been both supported and refuted using a variety of behavioral studies. Here, based upon neurophysiological data, I discuss the relationship amongst those neuronal substrates of action and the behavioral components of a movement. A novel view of reaching and grasping has been proposed which predicts that movements with similar kinematic and dynamic properties have a similar representation within the nervous system (Smeets & Brenner, 1999). However this is broadly inconsistent with a variety of neurophysiological findings that emphasize the independence amongst representations of action.

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Marcel Mutsaarts, Bert Steenbergen and Harold Bekkering

Anticipatory planning was examined in detail for a complex object manipulation task by capitalizing on both the complexity and the number of elements in the movement sequences in seven individuals with hemiparetic cerebral palsy (HCP) and seven left-handed control participants. Participants had to grasp a hexagonal knob using one of five possible grasping patterns as quicklly as possible following a starting cue (condition I), and sometimes, they had to rotate it subsequently either 60˚ or 120˚ clockwise or counterclockwise (condition II). In the first condition, the HCP participants appear to anticipate the comfort of the different grasping patterns before movement onset, as controls did. However, when the task consisted of more than one movement part, HCP participants did not complete their planning processes before movement onset, which was contrary to controls. Instead, the results suggest that they use a step-by-step planning strategy, that is, they planned the latter parts of a movement sequence as the movement unfolds. The results are discussed in the light of possible capacity limitations of an internal model for grip selection, and a recent model on the planning and on-line control of movement performance.

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Ching-yi Wu, Shih-han Chou, Mei-ying Kuo, Chiung-ling Chen, Tung-wu Lu and Yang-chieh Fu

Stroke patients are often left with hemiplegia or hemiparesis of the upper extremities, severely limiting the ability to perform bimanual and functional activities. No studies have investigated how stroke patients adapt their movements to changes in object size in functionally asymmetric bimanual tasks. The influence of object size on intralimb and interlimb coordination during an asymmetrical, functional bimanual task was examined in patients with left cerebral vascular accidents (LCVA) and healthy controls. Fourteen LCVA patients and 13 age-matched controls were instructed to reach to grasp a large and a small jar with the right/affected hand and to open the cap with the other hand. Movement kinematics was analyzed for intralimb coordination (spatial and temporal planning of reaching and grasping) and interlimb coordination (bimanual synchronization and temporal association of the hands). The results demonstrate a spatial adaptation of reaching in the affected hand to the object size and deficits in temporal planning of grasping with the affected hand to object size in the stroke patients. Movement adaptations of the unaffected hand in the stroke patients were similar to those in the healthy adults. Bimanual coordination was independent of object size for both groups.

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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.