Electrophysiological monitoring of low frequency auditory thresholds in humans using the Auditory Nerve Overlapped Waveform
Degree GrantorUniversity of Canterbury
Degree NameMaster of Audiology
Current methods of objectively measuring hearing thresholds at frequencies below 1000 Hz are not as accurate, or effective as obtaining hearing thresholds from the higher frequencies. The auditory nerve overlapped waveform (ANOW) was developed to allow accurate assessment of frequencies below 1000 Hz from the production of the cochlear microphonic, to develop a method of objective measure of low frequency hearing threshold. In the current evidence base, no one has yet successfully measured the ANOW in humans. This study aimed to produce the ANOW in humans to develop it as an objective measure of hearing threshold. We subjectively measured participant’s thresholds using both pure tone audiometry and electrocochleography. The participants were all suspected of having Ménière’s disease, and were undergoing transtympanic electrocochleography. We then used the electrocochleography needle to record our auditory responses. From these responses we derived the ANOW. Comparing the data analysed to the audiograms of the participants, we cannot conclude at this stage that the ANOW that we measured was purely neural from the apex of the cochlea in origin. The sound levels at which testing took place generally exceeded those levels which guaranteed that the ANOW waveforms recorded were purely neural in origin. From this, future studies in this area will involve stacked derived band masking to show frequency specificity and neural origin of the recordings. As such, the current results were not able to accurately predict participant thresholds. However this study has further advanced the technique of utilising the ANOW as an objective measure of low frequency hearing, to the benefit of future studies.