Summary

Mechanical contact on the body surface is an omnipresent feature of terrestrial life. We have shown here that such contact provides spatial information about the orientation of the body with respect to the environment. During reaching movements, the pattern of forces generated on the reaching hand when it contacts a surface provides a spatial mapping of hand location relative to the body. This spatial coding of terminal hand position is also extremely important for allowing adaptive changes in motor control to be implemented. In fact, in the absence of vision and contact cues, reaching accuracy rapidly degrades. Contact of the hand with the body itself provides a means by which the central nervous system representations of the body surface and its dimensions can be calibrated and updated over time. Hand contact with external auditory and visual objects localizes them spatially relative to the body, allowing directional calibration of vision and audition. The direction of gaze can be similarly calibrated. Light hand contact with stationary environmental objects greatly enhances the stability of stance. Finally, the control of the hands and feet themselves can be updated through physical interaction with objects in the external environment.

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