Hearing as substitution for sensation: a new principle for artificial sensibility

We describe a new principle for artificial sensibility of the hand based on sense substitution, using hearing as substitution for loss of sensation. The experiments were performed on 3 patients who had recently undergone isolated median nerve repair, 1 patient with replantation of an amputated forearm, 1 patient using a myoelectric prosthesis, and 4 patients using cosmetic prostheses. Small condenser microphones were mounted dorsally on the distal phalanges of multiple fingers of the nonsensate hands or prostheses. The friction sound, reflecting the vibrotactile stimuli generated by the moving touch of the objects, was picked up by the microphones and processed in a stereo amplifier that separated signals from individual fingers into different channels. The signals were transmitted to earphones, making possible a spatial resolution that enabled identification of each finger by the generated acoustic stimuli. Since the friction sound is characteristic of specific surfaces and textures, the corresponding acoustic stimuli made possible identification of different textures, such as glass, metal, wood, and paper, without using vision. We conclude that sense substitution using specifically processed acoustic stimuli as a substitute for sensation may represent a useful principle for generation of artificial sensibility in prostheses or hands lacking sensibility due to lesions in the peripheral or central nervous system or because of neurologic disease.