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  • 1
    Electronic Resource
    Electronic Resource
    Tactile input of the hand and the control of reaching to grasp movements (1997)
    Springer
    Experimental brain research 114 (1997), S. 130-137 
    Details
    ISSN: 1432-1106
    Keywords: Key words Motor control ; Somatosensory system ; Motor timing ; Arm kinematics ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The role of tactile information of the hand in the control of reaching to grasp movements was investigated. The kinematics of both reaching (or transport) and grasp components were studied in healthy subjects in two experimental conditions. In one condition (control condition) subjects were required to reach and grasp an object that could have two sizes and that could be located at two distances from the viewer. In the other condition (anaesthesia condition) the same movements were executed, but anaesthesia was provided to the subjects’ fingertips. In both conditions vision of the hand was prevented during movement. Anaesthesia affected mainly the kinematics of the first phase of grasping, that is, the finger-opening phase. This phase was lengthened and maximal finger aperture increased. In contrast, the duration of the successive phase (finger-closure) was poorly modified. The reaching component was also impaired by anaesthesia. Although the total extent of hand path and the spatial relations between the finger aperture and closure phases did not change between the two conditions, hand path variability increased. This occurred during transport deceleration phase and after the increase in variability of finger path. In addition, the whole movement was slowed down. The results of the present experiment suggest that tactile signals at the beginning and at the end of movement can be used to compute grasp time and to optimise grasp temporal parameters. Alternatively, signals from tactile receptors can be involved in encoding the position sense of the fingers. When this input is lacking, the control of grasp and in particular that of finger-opening phase can be impaired. Finally, the effect of the grasp impairment on the reaching component supports the notion that the coordination between reaching and grasping involves the whole temporal course of the two components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005612
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Visual distractors differentially interfere with the reaching and grasping components of prehension movements (1998)
    Springer
    Experimental brain research 122 (1998), S. 441-452 
    Details
    ISSN: 1432-1106
    Keywords: Key words Reaching-grasping ; Interference ; Human kinematics ; Implicit analysis of the object ; Attention
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In the present study we addressed the issue of how an object is visually isolated from surrounding cues when a reaching-grasping (prehension) movement towards it is planned. Subjects were required to reach and grasp an object presented either alone or with a distractor. In five experiments, different degrees of elaboration of the distractor were induced by varying: (1) the position of the distractor (central or peripheral); (2) the time when the distractor was suppressed (immediately or delayed, with respect to stimulus presentation); and (3) the type of distractor analysis (implicit or explicit). In addition, we tested whether the possible effects of the distractor on reaching-grasping were due to the use of an allocentric reference centered on it. This was obtained by comparing the effects of the distractor with those of a stimulus, the target of a placing movement successive to the reaching-grasping. The results of the five experiments can be summarized as follows. The necessary condition for an interference effect on both the reaching and the grasping components was the central presentation of the distractor. When the information on the distractor could be immediately suppressed, an interference effect was observed only on the grasp component. In the case of delayed suppression, an effect was found on the reaching component. Finally, when an overt analysis of the distractor was required, the interference effect disappeared. Two main conclusions have been drawn from the results of the present study. First, comparison between properties of the target and surrounding cues is performed by two independent processes for reaching and grasping an object. The process for the grasp relies more on allocentric cues than that for the reach. Second, when surrounding stimuli are automatically analyzed during visual search of the target, the process of visuo-motor transformation can incorporate their features into the target. In contrast, overt analysis of surrounding stimuli is performed separately from that of the target. Finally, the data of the present study are discussed in support of the premotor theory of attention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050532
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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