Effect of Different Types of Electrodes in Electrophonic Hearing

Abstract

The electrophonic effect, i.e., the sensation resulting from an electric current passed through the head, depends upon the kind of electrode system employed, a sinusoidal electric current giving rise to at least 5 phenomena: (1) with a moving electrode on the skin or on the roof of the mouth (fricative effect), the subject receives the strongest sensation, hearing either the 1st harmonic, or the 1st and 2nd harmonics, or the 2nd harmonic alone, depending upon the applied voltage and upon the placement and properties of the electrode; (2) with a large-area electrode any place on the skin of the head, if the skin is dry, the subject hears the 2nd harmonic, if it is wet, he hears nothing; (3) with the electrode immersed in a salt soln. in the ear, the subject hears a complex tone containing mostly the 2nd harmonic; (4) with the electrode on the mucous tissue inside the middle ear (with eardrum removed) the subject hears the 1st harmonic, a noise, or both; (5) with the electrode in contact with the epidermis of the meatus, the sub-ject hears the 1st harmonic, and at low frequencies may also hear a noise. The exptl. results indicate that the hearing of a tone under any of these 5 conditions is due to vibrations set up outside the cochlea, although there appear to be at least 4 different transducing mechanisms. Contrary to earlier hypotheses, the tympanic membrane is apparently not involved in the conversion of the electrical energy into mechanical vibration.