Experimentelle Untersuchungen zur bimanuellen Koordination als transiente Kopplung bei der Richtungsspezifikation
The accurate execution of bimanual movements is important for almost all work. At the same time, there is only a limited amount of appropriate and possible combinations. Limitations arise from the task itself, but the human movement system also causes limitations. They might be due to its mechanical properties or result from central nervous structures that control movement. As a matter-of-fact some movement combinations are impossible to execute, some are difficult, whereas others are easily and accurately executable. Therefore, it is necessary to take limitations and preferences of the human movement system into account when ergonomically designing a workplace. Spijkers and Heuer (1995) developed the hypothesis of transient coupling during the specification of movement parameters to explain (some) interference phenomena that can occur during bimanual movements. It states, that distortions of movement execution (may) result from mutual cross-talk between the two processes that specify the movement parameters. The cross-talk, so the basic assumption, arises from their initial coupling that dissipates when different parameter values are specified but is preserved in case of same values. This leads to the following predictions: First, specification of different values takes more time, because decoupling is necessary. Second, the time courses of the specification processes exhibit mutual assimilation that is strong in the beginning and weakens as specification proceeds and coupling dissipates. Third, the coupling causes the specification processes (and the respective movement characteristics) to covary. Hence, covariation should be observable in case of same values, in case of different values it is only present if specification still is incomplete, because coupling has not yet been abolished. The present study addressed whether the transient coupling hypothesis also holds for the specification of movement direction after it had already been proved for movement amplitude (e.g. Heuer, Spijkers, Kleinsorge, van der Loo, & Steglich, 1998) and isometric forces (Steglich, Heuer, Spijkers, & Kleinsorge, 1999). Five experiments were conducted to test the predictions by means of two experimental methods: the movement precuing technique that is used to estimate the time needed for parameter specification, and the timed response method that traces the time courses of the specification processes. The predictions concerning the delayed specification and the assimilation of the specification processes in case of different values were fully confirmed. A further important result was, that the human movement system treats egocentrically equivalent movement directions as equal (i.e., movements which are symmetrical to the mid-sagittal plane), whereas parallel (i.e., allocentrically equivalent) and incompatible (i.e., neither symmetric nor parallel) are different. Of special interest was, that, opposite to expectation, parallel directions exhibited an allocentric covariation with the coupling mode that caused this covariation being established during the process of specification (initially they were egocentrically coupled, and this coupling mode, as predicted, was preserved in case of symmetric directions). Incompatible directions, on the other hand, did not covary at all, i.e. coupling was abolished here. Recommendations based on current experimental work for workplace design are: 1) Bimanual actions should be executed symmetrically, especially if they have to be performed under time pressure. 2) Parallel execution should be preferred to incompatible combinations, but 3) in both cases there should be enough time for preparation and / or the system should tolerate the resulting error in movement execution.
info:eu-repo/classification/ddc/620, Ingenieurwissenschaften
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