Using vibrotactile feedback of instability to trigger a forward compensatory stepping response

We evaluated the effectiveness of vibrotactile feedback to enhance protective stepping with a view to developing a prosthesis for patients with balance disorders. Subjects standing on a moving walkway were exposed to an unpredictable, abrupt backwards translation of the support surface that required a step response to remain standing. The subjects were 15 normal young, 15 normal elderly and 9 patients with either bilateral vestibular loss or peripheral neuropathy. The initial passive displacement of the body was recorded by a gyroscope placed on the leg which triggered a vibration pulse to the trigeminal distribution on the forehead to cue a forwards step. Stepping responses and postural sway, with and without vibration feedback, were compared. Vibration produced significantly shorter stepping reaction times only in the elderly normals with naturally slower stepping. Patients did not benefit in any way. We conclude that the effectiveness of vibration biofeedback appears limited. Any enhancement of compensatory stepping might be triggered by speeding the decision to step rather than by creating a specific stimulus-response loop.