Sensory control of locomotion

Large numbers of sensory receptors provide feedback of movement in animals. Models are available that predict with reasonable accuracy the signals from force, length and velocity sensors in locomotion in cats. At the simplest reflexive level, muscles are under force, length and velocity feedback control. Recently it has been found that during locomotion, reflexes from force receptors reverse in sign, so that the mode of control is positive force feedback, which is kept stable by nonlinearities in the neuromuscular system. In gait the transitions from stance to swing depend on combinations of sensory signals. These can be expressed as finite state rules that are common to many species. The sensory trigger points for phase transitions are not fixed, but depend on each other, on the overall state of the limb and on behavioral set. It is argued that ensembles of sensory input "vote" for motor outcomes according to behavior-dependent weighting factors, are analogous to fuzzy control.