Is the organisation of goal-directed action modality specific? A common temporal structure

With the help of kinematic analysis, the temporal organization of the compl ex daily activity 'drinking from a bottle with a glass' was described in de tail. The analysis focused on the sequential action structure, the prehensi le acts, and the bimanual coordination as well as on the effect of differen t instruction modalities on these parameters to explore the underlying repr esentation for this complex action. Movements of the two arms were recorded in three-dimensional space with the help of an optoelectronic device in 12 normal subjects under four conditions: (1) action pantomime after verbal i nstruction; (2) action imitation after observation of the action performed by the experimenter without the objects; (3) action pantomime while seeing, but not touching the objects; and finally (4) action execution with object s. Despite high execution variability, the temporal structure of the action co uld be precisely described by the relative duration and peak velocity of ac tion segments, by the MGA-object size-correlation, and by linear regression analysis between the onsets of functionally related action segments. A sim ilar structure of the action as characterized by these kinematic parameters was retained across different instruction modalities. Only when the action was executed with the objects, the interval between the movement onsets of either hand and the peak velocity of the manipulative acts were reduced, w hile no change was observed across the other three instruction modalities. This stability of the temporal structure suggests the existence: of a Level in the representation of an action where all the modalities converge. (C) 2000 Elsevier Science Ltd. Ail rights reserved.