[Phantom responses and early auditory evoked potentials. Comparison of the TDH39 hearing aid and an intra-canal...

Using conventional tonal audiometry, Joseph Zwislocki demonstrated in 1953 that the intensity of sound transfer to the opposite ear depends on the transductor (earphone). Interauricular attenuation is inversely proportional to the bone surface facing the earphone when all air transmission has been eliminated. In earlier work in 1982, we first concluded that this rule is applicable to auditory evoked potentials such as those used for conventional audiometry for unilateral cophosis. A TDH39 device transfers the sound to the contralateral ear with an attenuation of approximately 60 decibels, using the V wave latency as reference for calculating intensity. We verified the reality of Joseph Zwislocki's rule with newly available insert earphones. Surface contact with bone being smaller than with the TDH39, sound transfer to the opposite ear would logically be much more attenuated when air transmission is eliminated. The aim of this work was to determine sound transfer in 27 patients with unilateral cophosis undergoing conventional audiometry and to draw practical conclusions.