Use of distortion product otoacoustic emissions to assess middle ear transducers in rhesus monkeys.

Distortion product otoacoustic emissions (DPOAEs) can provide an objective and noninvasive assessment of the peripheral cochlear function. Auditory brainstem responses measured from implanted rhesus monkeys have shown that middle ear transducers, coupled directly to the incus, are capable of delivering the signals to the central auditory system. The DPOAEs were used as a noninvasive method of assessing the frequency specificity of this mechanical transduction. In two rhesus monkeys implanted with the middle ear transducers, one primary stimulating tone (f1) was presented acoustically, and the other primary tone (f2) was presented by the transducer, which converted the signal into a mechanical motion of the probe tip attached to the body of the incus. The nonlinear characteristics of the cochlea produced the distortion product responses at the expected frequencies (2f1 - f2). This demonstrates the fidelity of the middle ear implant signal transduction in vivo. The DPOAEs also indicate minimal changes in the post-implant middle ear transmission. This study demonstrates that the DPOAEs can be used to assess the function of implanted middle ear transducers objectively and noninvasively.