Authors: Vaclav Vencovsky¹
¹Czech Technical University in Prague
Background: Distortion-product otoacoustic emissions (DPOAE) growth functions—DPOAE amplitudes as a function of stimulus level—can be used to estimate the DPOAE threshold, which correlates with the absolute hearing threshold. However, their clinical use is limited because the shape and level of these functions are affected not only by cochlear amplifier gain but also by middle-ear forward and reverse transmission.
Method: A cochlear model was used to predict DPOAEs for various stimulus levels, creating a “DPOAE level map.” Maps derived with uniformly set amplification (1–6 kHz) were aligned to indicate distortion invariance. DPOAE growth functions were measured using the “scissor paradigm” and fitted into simulated maps for various gains to determine the specific cochlear amplifier gain.
Results: DPOAE growth functions proved highly sensitive to changes in cochlear amplifier gain. Even variations within the normal audiometry range (20 dB) yielded strong changes in the growth function shape. For example, at 2 kHz, a subject with a 5 dB HL threshold (s001) fitted a model gain of 53 dB, while a subject with a 20 dB HL threshold (fav3) corresponded to a model gain of 29 dB.
Conclusion: The proposed alignment with simulated DPOAEs provides a time-efficient framework for measuring growth functions without needing to pre-determine optimal stimulus levels. This technique is suitable for use with swept stimuli, facilitating the separation of the distortion and reflection components of DPOAEs.
