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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 68-76 
    ISSN: 1432-1106
    Keywords: Key words Human ; Kinematics ; Tool-use ; Movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In traditional reach-to-point and reach-to-grasp studies an increase in accuracy demands typically results in a lengthening of the deceleration phase of the reach and a freezing of the more distal joints. The purpose of the present experiment was to examine whether similar changes in the reach kinematics could be observed during a tool-using skill, as would be predicted from an effector independence perspective. Five subjects were required to eat two substances (i.e. a solid and a liquid one) that imposed different requirements on the accuracy of the movement. The subjects transported the substances from the plate into the mouth. A prolonged movement duration was found for the liquid as compared to the solid substance. However, rather than being exclusively due to a lengthening of deceleration phase, the larger movement duration resulted from a slowing down of the whole movement. Therefore, the skewed velocity profiles found in the traditional reach-to-grasp studies may well be the result of the accuracy demands only impinging on the final part of the movement trajectory, rather than being a consequence of central, effector-independent, organising principles. In addition, under increased accuracy demands subjects were shown to redistribute their movement in a proximodistal direction. Movements of the distal components were reduced to a minimum and the involvement of trunk and head movement increased.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 362-368 
    ISSN: 1432-1106
    Keywords: Key words Binocular ; Monocular ; Disparity ; Vergence ; One-handed catching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The aim of this study was to examine the role of binocular and monocular information sources in specifying time-to-contact. More specifically, it was investigated whether the timing of the one-handed catch is consistent with a binocular tau-function strategy. Subjects (n=8) were required to time their grasp to catch a ball approaching with a constant spatial trajectory. The ball approached at three different constant velocities (1.5, 2.0 and 2.5 m/s). Vergence and disparity were manipulated through subjects wearing a telestereoscope to increase the effective interocular separation, under both binocular and monocular viewing. Subjects performed 24 trials in each of the four conditions. Subjects’ started the opening of the hand earlier in the binocular telestereoscope condition when a ball approached with velocity of 1.5 m/s. They then closed the hand earlier in the binocular telestereoscope condition at all ball approach velocities. There were no effects of telestereoscope on the timing of hand opening and closing under monocular viewing. This finding suggests the use of the binocular information in timing the grasp. However, there were effects of approach velocity under all conditions of monocular and binocular viewing. Subjects’ closed the hand earlier as a function of increasing approach velocity. Together, the effects of the telestereoscope and approach velocity indicate that timing of the one-handed catch is not consistent with the use of a binocular ”tau-function” variable. Rather, it is concluded that multiple sources of monocular and binocular information contribute to the regulation of timing.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 369-377 
    ISSN: 1432-1106
    Keywords: Key words Adaptation ; Selection ; Re-calibration ; Timing ; One-handed catching ; Binocular information
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract   A pre-exposure, exposure, post-exposure design was used to assess the adaptation of the timing of a one-handed catch during telestereoscopic viewing. More specifically, it was examined whether the adaptation involved: (1) ignoring binocular sources of information and selecting other information, or (2) a recalibration of the coupling between the effected binocular information and the catching movement, and (3), if it is recalibration, whether it is restricted to the manipulated binocular information. To test these hypotheses, subjects (n=16) were assigned to one of two groups, each group performing three blocks of 15 trials in the dark with only the ball visible. In the exposure condition, both groups were required to catch balls under binocular telestereoscopic viewing. In the pre-exposure and post-exposure conditions, subjects performed under binocular and monocular viewing, respectively. Kinematics of the grasping movement were recorded. It was predicted that, in the case of a selection process, no afterfeffects would occur in the post-exposure condition, whereas, in the case of recalibration, aftereffects would occur. Moreover, if the recalibration is restricted to the manipulated information, only the group that was provided with binocular vision during the pre- exposure and post-exposure conditions would show aftereffects. Significant condition (pre-exposure, exposure, post-exposure) by block (first three trials, last three trials) effects were found for the moments of grasp onset, peak opening velocity and hand closure, indicating that the hand was opened and closed earlier in the first three trials of telestereoscopic viewing. This coincided with an increase in catching failures. In addition, for the moments of hand closure and peak closing velocity, negative aftereffects were found in the post-exposure condition. The hand was closed later in the first three trials after removal of telestereoscope. With respect to the presence of the aftereffects, no differences were found between the groups. It was concluded that adaptation to telestereoscopic viewing in the timing of a one-handed catch is due to the recalibration of the coupling between information and movement, rather than a selection of another source of information. Moreover, it is likely that the recalibration was not restricted to the single, manipulated information. Rather, the recalibration involves multiple binocular and monocular optical and oculomotor sources of information.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Experimental Child Psychology 58 (1994), S. 510-528 
    ISSN: 0022-0965
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Psychology
    Type of Medium: Electronic Resource
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