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  • 1
    ISSN: 1432-1106
    Keywords: Upper-limb coordination ; Synergies ; Parallel control ; Skill learning ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary When movements are performed together in the upper-limbs, a strong tendency emerges to synchronize the patterns of motor output. This is most apparent when trying to do different things at the same time. The present experiment explored the simultaneous organization and control of spatiotemporally different movements. There were two practice conditions: symmetrical and asymmetrical. In the symmetrical condition, subjects performed a series of unidirectional elbow flexion movements, followed by a series of elbow flexion-extension-flexion (reversal) movements in both limbs simultaneously. In the asymmetrical practice condition, subjects performed the unidirectional movement in the left limb together with the reversal movement in the right limb. Findings revealed a tendency for each limb movement to assimilate the features of its counterpart under the latter condition. This effect was “asymmetrical” in that the unidirectional movement was more attracted to the reversal movement than vice versa. Nevertheless, subjects were able to partly suppress this synchronization tendency as was evident from the moderate cross correlations between the angular acceleration patterns of both limb movements and from an increasingly successful differentiation of the activity levels in the right and left limb muscles. All together, these findings provide evidence for some degree of parallel control of spatiotemporally different actions. The data are discussed in view of the possible suppression of a bilaterally distributed motor control system, that is mainly held responsible for activiting proximal limb musculature.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Key words Bimanual rhythmic movement ; Interlimb coordination ; Planes of motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Two dominant coordination constraints have been identified during isofrequency conditions in previous work: the egocentric constraint, i.e., simultaneous activation of homologous muscle groups, and the allocentric constraint, i.e., moving the segments in the same direction in extrinsic space. To verify their generalization, bimanual drawing movements were performed in different planes of motion (transverse, frontal, sagittal, frontal-transverse) according to the in-phase and anti-phase mode along the X- and Y-axes. Convergent findings were obtained across the transverse, frontal, and frontal-transverse planes. The in-phase mode along both axes was performed most accurately/consistently, whereas the anti-phase mode resulted in a deterioration of the coordination pattern and this effect was most pronounced when the latter mode was introduced with respect to both dimensions. For sagittal plane motions, the in-phase mode was again superior but the second most optimal configuration was the anti-phase mode along both axes. This finding was hypothesized to result from the familiarity with the pattern since it resembles cycling behavior. It illustrates how cognitive mapping is superimposed onto the dynamics of interlimb coordination. Overall, these results support the presence of both the egocentric and allocentric constraint during bimanual movement production.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1106
    Keywords: Interlimb coordination ; Kinesthetic afferences ; Passive movement ; Relative phase ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The disruption of three patterns of two-limb coordination, involving cyclical flexion-extension movements performed in the same or in different directions, was investigated through application of passive movement to a third limb by the experimenter. The three patterns referred to the homologous, homolateral, and heterolateral (diagonal) limb combinations which were performed in the sagittal plane. The passive movement involved a spatiotemporal trajectory that differed from the movements controlled actively. Even though subjects were instructed to completely ignore the passive limb movement, the findings of experiment 1 demonstrated a moderate to severe destabilization of the two-limb patterns, as revealed by analyses of power spectra, relative phase, cycle duration, and amplitude. This disruption was more pronounced in the homolateral and heterolateral than in the homologous effector combinations, suggesting stronger coupling between homologous than nonhomologous limb pairs. Moreover, passive mobilization affected antiphase (nonisodirectional) movements more than inphase (isodirectional) movements, pointing to the differential stability of these patterns. Experiment 2 focused on homolateral coordination and demonstrated that withdrawal of visual information did not alter the effects induced by passive movement. It was therefore hypothesized that the generation of extra kinesthetic afferences through passive limb motion was primarily responsible for the detriment in interlimb coordination, possibly conflicting with the sensory information accompanying active movement production. In addition, it was demonstrated that the active limbs were more affected by their homologous passive counterpart than by their non-homologous counterpart, favoring the notion of “specific” interference. The findings are discussed in view of the potential role of kinesthetic afferences in human interlimb coordination, more specifically the preservance of relative phasing through a kinesthetic feedback loop.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1106
    Keywords: Key words Parkinson’s disease ; Motor learning ; Interlimb coordination ; Basal ganglia ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The basal ganglia have traditionally been associated with motor control functions and this view has prevailed since the late nineteenth century. Recent experimental studies suggest that this neuroanatomical system is also critically involved in motor learning. In the present study, motor learning/transfer capabilities were compared between patients with Parkinson’s disease and a group of normal elderly people. Subjects practiced a bimanual coordination task that required continuous flexion-extension movements in the transverse plane with a 90° phase offset between the forearms. During acquisition, augmented visual feedback of the relative motions was provided in real time. The findings revealed improvements in the bimanual coordination pattern across practice in both groups when the augmented concurrent feedback was present. However, when transferred to performance conditions in which the augmented information was withheld, performance deteriorated (relative to the augmented condition) and this effect was more prevalent in the Parkinson patients. More specifically, no improvement in interlimb coordination was observed under nonaugmented feedback conditions across practice. Instead, a drift toward the preferred in-phase and anti-phase coordination patterns was evident. The present findings suggest that Parkinson patients can improve their performance on a new motor task, but they remain strongly dependent on augmented visual information to guide these newly acquired movements. The apparent adoption of a closed-loop control mode is accompanied with decreases in movement speed in order to use the feedback to ensure accuracy. When the augmented feedback is withheld and the movement pattern is to be controlled by means of intrinsic information feedback sources, performance is severely hampered. The findings are hypothesized to indicate that learning/transfer is affected in Parkinson patients who apparently prefer some constancy in the environmental contingencies under which practice takes place. The present findings are consistent with the notion that the basal ganglia form a critical neuroanatomical substrate for motor learning.
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  • 5
    ISSN: 1432-1106
    Keywords: Key words Multijoint movement control ; Elbow-wrist movement ; Interactive torques ; Coordination pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The present paper focused on the role of mechanical factors arising from the multijoint structure of the musculoskeletal system and their use in the control of different patterns of cyclical elbow-wrist movements. Across five levels of cycling frequency (from 0.45 Hz up to 3.05 Hz), three movement patterns were analyzed: (1) unidirectional, including rotations at the elbow and wrist in the same direction; (2) bidirectional, with rotation at the joints in opposite directions, and (3) free-wrist pattern, which is characterized by alternating flexions and extensions at the elbow with the wrist relaxed. Angular position of both joints and electromyographic activity of biceps, triceps, the wrist flexor, and the wrist extensor were recorded. It was demonstrated that control at the elbow was principally different from control at the wrist. Elbow control in all three patterns was similar to that typically observed during single-joint movements: elbow accelerations-decelerations resulted from alternating activity of the elbow flexor and extensor and were largely independent of wrist motion at all frequency plateaus. The elbow muscles were responsible not only for the elbow movement, but also for the generation of interactive torques that played an important role in wrist control. There were two types of interactive torques exerted at the wrist: inertial torque arising from elbow motion and restraining torque arising from physical limits imposed on wrist rotation. These interactive torques were the primary source of wrist motion, whereas the main function of wrist-muscle activity was to intervene with the interactive effects and to adjust the wrist movement to comply with the required coordination pattern. The unidirectional pattern was more in agreement with interactive effects than the bidirectional pattern, thus causing their differential difficulty at moderate cycle frequencies. When cycling frequency was further increased, both the unidirectional and bidirectional movements lost their individual features and acquired features of the free-wrist pattern. The deterioration of the controlled patterns at high cycling frequencies suggests a crucial role for proprioceptive information in wrist control. These results are suppportive of a hierachical organization of control with respect to elbow-wrist coordination, during which the functions of control at the elbow and wrist are principally different: the elbow muscles generate movement of the whole linkage and the wrist muscles produce corrections of the movement necessary to fulfill the task.
    Type of Medium: Electronic Resource
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