Abstract
BackgroundFor lower-limb amputees, wearing a prosthetic limb helps restore their motor abilities for daily activities. However, the prosthesis's potential benefits are hindered by limited somatosensory feedback from the affected limb and its prosthesis. Previous studies have examined various sensory substitution systems to alleviate this problem; the prominent approach is to convert foot-ground interaction to tactile stimulations. However, positive outcomes for improving amputees' postural stability are still rare. We hypothesize that the intuitive design of tactile signals based on psychophysics shall enhance the feasibility and utility of real-time sensory substitution for lower-limb amputees. MethodsWe designed a wearable device consisting of four pressure sensors and two vibrators and tested it among the unilateral transtibial amputees (n=7) and the able-bodied (n=8). The real-time measurements of foot pressure were fused into a single representation of foot-ground interaction force, which was encoded by varying vibration intensity of the two vibrators attached to the participants’ forearm. The layout of vibrators was spatially congruent with the foot force sensors' placement; the vibration intensity followed a logarithmic function of the force representation, in keeping with principles of tactile psychophysics. The participants were tested with a classical postural stability task in which visual disturbances perturbed their quiet standing. ResultsWith a brief familiarization of the system, the participants exhibited better posture stability against visual disturbances when switching on sensory substitution than without. The body sway was substantially reduced, as shown in head movements and excursions of the center of pressure. The improvement was present for both amputees and able-bodied controls and was particularly pronounced in more challenging conditions with larger visual disturbances. ConclusionsSubstituting otherwise-missing foot pressure feedback with vibrotactile signals can improve postural stability for lower-limb amputees. The intuitive design of the mapping between the foot-ground interaction force and the tactile signals is essential for the user to utilize the surrogated tactile signals for postural control, especially for situations that their postural control is challenged.
Bicycling Phase Recognition for Lower Limb Amputees Using Support Vector Machine Optimized by Particle Swarm Optimization