Speaker
Description
Distortion-product otoacoustic emission (DPOAE) level maps measured across audiological frequencies differ. Keefe JASA 111:249–260 (2002) suggested that if the distortion characteristics of the basilar membrane (BM) are uniform along a large part of its length, the differences in DPOAE level maps across frequencies from 0.5 kHz to 8 kHz should reflect the forward and reverse transmission of the middle ear. We use a cochlear model that accounts for longitudinal hydrodynamic coupling via cochlear fluids between individual BM segments. At each segment, a memory less spatially uniform nonlinearity is applied to the feedback force to generate DPOAEs. The model was designed to produce roughly uniform amplification of approximately 50 dB of transversal BM motion at characteristic frequencies from 1 to 6 kHz. DPOAE level maps in this frequency range derived from this model were aligned by applying level shifts comparable to shifts between BM input/output functions. Therefore, the model supports the distortion invariance hypothesis. We took average DPOAE growth functions from Abdala et al. Ear Hear. 42:832–845 (2021) and fitted them into the DPOAE level map simulated at 2 kHz. The smallest fitting error was obtained for DPOAE growth functions measured for young, normally hearing subjects. The error increased for middle-aged and older subject groups in which the cochlear nonlinearity is altered in comparison to the young group. The fitting procedure can be used to estimate the onset of compression in the BM input/output functions across frequencies.