Sensory and motor interdependence in postural adjustments.

The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for postural adjustments for healthy subjects and certain types of vestibular patients. The sensorimotor control structures for patients with absent vestibular function suggest implications for management of the deficit.