Using a concha electrode to measure response patterns based on the amplitudes of cochlear microphonic waveforms across acoustic frequencies in normal-hearing subjects.

OBJECTIVES

Compared to a conventional click-evoked cochlear microphonic (CM) in an electrocochleogram, a tone-burst evoked CM waveform (CMW) is unconventional and the frequency band is narrower. Furthermore, compared to conventional CM measurement techniques such as the use of a tympanic or a canal electrode, the use of a concha electrode is the least invasive and an unconventional technique in the measurement of CMs. Finally, compared to CM responses measured by conventional approaches, the response pattern obtained from the amplitude of far-field recorded CMWs across acoustic frequencies is unconventional. Our objective is to combine these three unconventional elements together into a unique approach, which may provide potential benefits for clinical diagnosis and cochlear research.

DESIGN

Using a concha electrode, CMWs in response to a 14 msec tone burst were recorded in seven normal-hearing subjects. The CMW amplitudes recorded over different acoustic frequencies were compared to each other to produce a frequency response pattern.

RESULTS

Two features were observed in the response pattern: the CMW amplitude decreased upon an increase in frequency of a tone burst stimulus, and the decrease occurred faster at lower frequencies than at higher frequencies.

CONCLUSIONS

We confirmed a measurable CMW response pattern using the concha electrode. We propose that the pattern's features may be partly due to variation along the cochlea of the activities and volume of hair cells and possibly also the physical properties of the basilar membrane. The clinical importance of these results may be related mainly to seven features of the CMW, including electrode locations, response patterns, inclusion of low frequencies, and uniqueness of CMWs (versus otoacoustic emissions, auditory brainstem responses, shorter stimulus, and audiograms). Limitations, such as signal to noise ratio, also exist. After further study, the concha electrode may be used in the clinic and in research, and the response pattern may be used to interpret the CMW measurement.