Conditions for elimination of interaction in two-component arm movements

Ballistic multi-component movements show strong interaction between components of the movement; the lime for the first component of a two-component movement is dependent on the geometrical conditions for the second component and vice versa. The component times are each described in terms of the square-root of amplitudes of the two components. Independence of the component movement times was achieved by the introduction of an activity intervening between performance of the two components. The movement times for each component were found to be not significantly different and not to be influenced by the following or preceding component and could then be modelled in terms of the square-root of the movement amplitude. Although independence of components was established, the component times were higher than the single component movement time. The effect of incentive and an inter-component activity was tested to see if it was possible to obtain movement times of the two task components which were the same as the single-component movement times. The major effect on movement times was found to be the intervening activity with incentive having only a minor effect, With intervening activity the movement times were not significantly different for the two components of the task, nor were they different from the single-component movement time. Incentive had a significant effect only on the first component of a two-component sequential movement.