Eye-Hand Coordination for 3-D Oriented Objects

When reaching for an object in space, the di~t~ance of the object, its orientation and shape should all be correctly estimated well before the hand arrives in contact wit,h the object. We investigate here how the visual information about the object's orientation is incorporated into the motor program which guides the hand to the vicinity of the object. This motor program governs in particular the transportation of the hand, the opening of the hand, and the rotations of the forearm and wrist. These variables are analyzed in the light of the "visuo-motor channels" framework proposed by Jeannerod (1981), in which the information about the object's distance and shape is processed independently, from perception to action. Our results seem to favor an alternative framework, in which an interpretation of the threedimensional world should be built before a motor command can be generated. Due to time constraints, this mechanism appears to be mainly feedforward.