Fig. 2

Illustration of the sensory substitution system. A The insole is instrumented with four thin electropiezo force sensors whose measurements are routed to a tablet for real-time data processing. The measured force determines the vibration intensity of the two tactile vibrators attached along the forearm's longitudinal axis on the same side of the insole. When participants walk or stand still, the vibration provides real-time feedback of the balance performance from the measured foot. B The vibration intensity follows a logarithmic relationship with the balance index (BI), which is determined by the changing force loading caused by body sway. Forward or backward body lean would lead to one vibrator working, respectively