Effect of motor and sensory noise in the control of upright standing.

Quiet standing has been modeled many times as an unstable task of controlling an inverted pendulum in a gravity divergent force field. Multiple sensory systems and motor components of the nervous system are involved in postural balancing and the stabilization problem becomes even more complex in presence of perturbations. In the present work, we reveal how humans deal with different sources of perturbations. We asked healthy participants to perform a realistic whole body postural balancing task, controlling a perturbed virtual inverted pendulum through an EMG-interface connected to the ankle muscles, receiving a haptic feedback of the pendulum position. Two sources of perturbations were provided: Motor Noise, applying a gain on the control signal, and Sensory Noise, adding an external disturbance on the system plant. Results show that participants, without a priori knowledge on perturbations and no specific instructions, were able to adapt to perturbations and behaved in different ways in relationship with the different perturbation sources. These findings also suggest that error-enhancing methods (i.e., perturbations) might be suitable for postural stability recovery.