Recognising a hand by grasp

The present study aimed to demonstrate that motor representations are used to recognise biological stimuli. In three experiments subjects were require d to judge laterality of hands and forearms presented by pictures. The post ures of the hands were those assumed when holding a small, medium and large sphere. In experiment 1, the sphere held in hand was presented, whereas in experiment 2 it was absent. In experiment 3, the same images, showing hold ing-a-sphere hands, as in experiment 1 were presented, but without forearm. In all experiments one finger of each hand could be absent. In experiment 1 recognition time was longer for those hand postures for which the corresp onding grasping motor acts required more accuracy. This was confirmed by a control experiment (experiment 4), in which subjects actually grasped the s pheres. Absence of fingers did not influence right-left hand recognition. H owever, the absence of target object in experiment 2, and of forearm in exp eriment 3 reduced the effects of the type of holding on hand laterality rec ognition. The results of the present study indicate that grasp representati ons are used to recognise hand laterality. In particular, the visual descri ption of how hand and object interact in space (the opposition space [M.A. Arbib, Programs, schemas and neural networks for control of hand movement: beyond the RS frameworks, in: M. Jeannerod (Ed.), Attention and Performance XIII: Motor Representation and Control, Lawrence Erlbaum, Hillsdale, NJ, 1 990, 111-138; M.A. Arbib, T. Iberall, I). Lyons, Coordinated control progra ms for movements of the hand, in: A.W. Goodman, I. Darian-Smith (Eds.), Han d function and the neocortex, Springer, Berlin, 1985, pp. 135-170]) and the anchoring of the hand to the agent are the features of the grasp represent ations used in hand-recognition processes. The data are discussed according to the more general notion that motor representations are automatically ex tracted in the process of intuiting situations, or people's intentions. The se motor representations, which are compared with those of other people, co ntain concrete information on the actions (the motor program) by which a si tuation is created and on the aim of the agents executing those actions. (C ) 2000 Elsevier Science B.V. All rights reserved.