Active and passive movements in the calibration of position sense*

Spatially coordinated behavior is possible only because many features of the body's structure and of the structure of the world are highly predictable. From the primitive chaos of the impressions collected by our sense organs, a system of stable and permanent spatial referents progressively emerges in relation to the moving and ever-changing framework of bodily positions. The prerequisite to the building up of motor strategies directed at the outside world lies in the establishment of a known system of spatial relationships among the different mobile parts of the body and a method of evaluating continuously their relative positions. The initial and final positions of any moving segment must primarily be referred to the proprioceptive spatial schema upon which the various displacements related to each joint of the bony frame may be ordered. Studies devoted to position sense have, for the most part, focused upon the problem of kinaesthesis in order to gain knowledge of our ability to estimate changes in position of our joints and to reproduce these changes with more or less precision in distance, speed, and direction. They have tended to neglect the problem of the calibration of these positions in the spatial reference system of the body, which is itself situated within, or moves itself in, invariant perceptual space. This is a problem which places the study of kinesthetic sensation at the level of the mechanisms which confer upon it its “local sign.” __________