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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms for distance reproduction in perceptual and motor tasks (1996)
    Springer
    Experimental brain research 108 (1996), S. 140-146 
    Details
    ISSN: 1432-1106
    Keywords: Perception ; Visuo-motor transformation ; Distance reproduction ; Pointing ; Internal representation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Two experiments were carried out: the control experiment and the doubling-distance experiment. In the control experiment subjects were presented with two visual stimuli whose distance was randomly varied. Subjects were required to reproduce the interstimulus remembered distance in two conditions. In one condition (reproduction by pointing) they pointed to a virtual position in space. In the other condition (visual reproduction) they matched the distance by using two other visual stimuli. In the doubling-distance experiment, distances between the two randomly presented stimuli were half of the distances used in the control experiment. Subjects were required to reproduce the double of the presented distance. As in the control experiment, reproduction was executed in two conditions: reproduction by pointing and visual reproduction. In both experiments variable and constant errors were measured. Pointing kinematics were also analysed. The results of the control experiment showed that subjects underestimated distance in reproduction by pointing, whereas they overestimated distance in visual reproduction. Variable errors increased with increasing distance, whereas they were not influenced by the type of reproduction. In the doubling-distance experiment, subjects generally overestimated distance by the same amount in both conditions. However, overestimation decreased with distance during reproduction by pointing. Pointing kinematics varied between the two experiments. The results of the control experiment confirm the hypothesis that perceptual judgement and visuo-motor transformation are two separate processes during which the same object attributes are independently analysed. However, the results of the doubling-distance experiment suggest that perceptual judgement and visuo-motor transformation use the same mechanisms when object attributes are deduced by mental elaboration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242911
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  • 2
    Electronic Resource
    Electronic Resource
    Planning an action (1997)
    Springer
    Experimental brain research 115 (1997), S. 116-128 
    Details
    ISSN: 1432-1106
    Keywords: Key words Motor act ; Reaching-grasping ; Placing ; Kinematics ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The motor control of a sequence of two motor acts forming an action was studied in the present experiment. The two analysed motor acts were reaching-grasping an object (first target) and placing it on a second target of the same shape and size (experiment 1). The aim was to determine whether extrinsic properties of the second target (i.e. target distance) could selectively influence the kinematics of reaching and grasping. Distance, position and size of both targets were randomly varied across the experimental session. The kinematics of the initial phase of the first motor act, that is, velocity of reaching and hand shaping of grasping, were influenced by distance of the second target. No kinematic difference was found between movements executed with and without visual control of both hand and targets. These results could be due to computation of the general program of an action that takes into account extrinsic properties of the final target. Conversely, they could depend on a visual interference effect produced by the near second target on the control of the first motor act. In order to dissociate the effects due to second target distance from those due to visual interference, two control experiments were carried out. In the first control experiment (experiment 2) subjects executed movements directed towards spatial locations at different distances from the first target, as in experiment 1. However, the near second target was not presented and subjects were required to place the object on an arbitrary near position. Distance of the second (either real or arbitrary) target affected the reaching component of the first motor act, as in experiment 1, but not the grasp component. In the second control experiment (experiment 3), the pure visual interference effect was tested. Subjects were required to reach and grasp the object and to lift it in either presence or absence of a second near stimulus. No effect on the initial phase of the first motor act was observed. The results of the this study suggest a dissociation in the control of reaching and grasping, concerning not only visual analysis of extrinsic properties of the immediate target but also visual analysis of the final target of the action. In other words, the notion of modularity for the motor control can be extended to the construction of an entire action.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005671
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  • 3
    Electronic Resource
    Electronic Resource
    The control of an action in Parkinson’s disease (1999)
    Springer
    Experimental brain research 129 (1999), S. 269-277 
    Details
    ISSN: 1432-1106
    Keywords: Key words Parkinson’s disease ; Kinematics ; Action ; Reaching-grasping ; Placing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We studied, in Parkinson’s disease (PD) patients and healthy control subjects, the kinematics of the action formed by two successive motor acts: reaching-grasping an object (first target) and placing it on a second target. We examined the effects of extrinsic (i.e., distance) and intrinsic (i.e., size) properties of the second target on the various kinematic phases of reaching-grasping. We randomly varied distance and size of both stimuli across the experimental session. The kinematics of the reach initial phase of both patients and controls was influenced by the distance of both the first and the second target. In particular, peak acceleration increased for farther position of the second target. However, in the subsequent phase, patients, differently from controls, modified their reaching kinematics, removing the effects of second target position. These results were due neither to a visual interference effect of the second target on reaching-grasping nor to the complexity of movement sequence. Finally, the size of the second target did not affect grasp kinematics of both patients and controls. The results of the present study support the hypothesis that PD patients are able to compute the general program of an action in which extrinsic properties of both the actual and the final target are computed. However, PD patients re-program movement during its execution. This suggests a decay of the motor program. That is, basal ganglia can be involved in storing the plan of an action and in controlling its correct execution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050897
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    Paper (German National Licenses)
    Fulltext
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