Designing vibrotactile balance feedback for desired body sway reductions.

Vibrotactile feedback about body position and velocity has been shown to be effective at reducing low frequency body sway (below about 0.5 Hz) in response to balance perturbations while standing. However, current devices cause an undesirable increase in high frequency body sway. In addition, unlike other sensory prostheses such as hearing aids, which are fine-tuned to the user, current vibrotactile balance prostheses largely employ a "one size fits all" approach, in that they use the same settings (i.e. parameter values) for all subjects. Rather than using a fixed design consisting of position and velocity feedback for all subjects, we propose a "custom design" approach that employs system identification methods to identify the feedback required to achieve a desired body sway frequency response for the subject. Our derivations and simulations show that in order to accomplish this objective, feedback consisting of a subject-specific filtered combination of body position, velocity and acceleration is required. Simulation results are provided to illustrate the results.