Implantable hearing aids: changes in the auditory-evoked potential of the monkey in response to increased loading of the stapes.

This study examines the effects on the hearing response in the monkey resulting from an increasing load on the stapes exerted by an implantable middle ear transducer. The transducer was placed on the distal end portion of the long process of the incus in monkeys and progressively advanced in small increments in the direction of the long axis of the stapes. Auditory-evoked potentials were recorded to assess the hearing response induced by the vibration of the transducer at each point. A decrease in response equivalent to a change in stimulus sound pressure level of approximately 20 dB occurred as the load on the stapes increased. Frequency response may also change. Our results imply that, to achieve maximum efficiency, the load placed on the ossicles by a vibrating transducer must be minimized.