Nonlinear reflection as a cause of the short-latency component in stimulus-frequency otoacoustic emissions simulated by the methods of compression and suppression.

Václav Vencovský,Anthony W Gummer,Aleš Vetešník

doi:10.1121/10.0001394

Abstract

Stimulus-frequency otoacoustic emissions (SFOAEs) are generated by coherent reflection of forward traveling waves by perturbations along the basilar membrane. The strongest wavelets are backscattered near the place where the traveling wave reaches its maximal amplitude (tonotopic place). Therefore, the SFOAE group delay might be expected to be twice the group delay estimated in the cochlear filters. However, experimental data have yielded steady-state SFOAE components with near-zero latency. A cochlear model is used to show that short-latency SFOAE components can be generated due to nonlinear reflection of the compressor or suppressor tones used in SFOAE measurements. The simulations indicate that suppressors produce more pronounced short-latency components than compressors. The existence of nonlinear reflection components due to suppressors can also explain why SFOAEs can still be detected when suppressors are presented more than half an octave above the probe-tone frequency. Simulations of the SFOAE suppression tuning curves showed that phase changes in the SFOAE residual as the suppressor frequency increases are mostly determined by phase changes of the nonlinear reflection component.

Highlights

The group delay of SFOAEs simulated in a twodimensional cochlear model by the method of compression a)Electronic mail: anthony.gummer@uni-tuebingen.de (Kemp and Chum, 1980)—in which the model was stimulated with a 20-dB sound pressure level (SPL) test tone and 60-dB SPL compressor—was in some cases shorter than twice the group delay calculated from simulated iso-intensity BM responses (Vencovsky et al, 2018)
We investigate the reason for the shorter SFOAE delays emanating from the cochlear model
Shera et al (2008) suggested nonlinear reflection due to the suppressor as a possible cause of the short-latency component in the experimentally measured SFOAEs, and our study provides theoretical evidence that these artifacts may be generated in the cochlear model due to a suppressor or a compressor

Summary

Introduction

(Kemp and Chum, 1980)—in which the model was stimulated with a 20-dB sound pressure level (SPL) test tone and 60-dB SPL compressor—was in some cases shorter than twice the group delay calculated from simulated iso-intensity BM responses (Vencovsky et al, 2018). Berezina-Greene and Guinan (2015) showed that near the minima of SFOAE fine structure in a plot of SFOAE amplitude as a function of stimulus frequency, time-frequency analysis revealed two components with slightly shorter and slightly longer delay than expected for a component generated in the peak region of the traveling wave They explained that these components are pronounced because the wavelets reflected from the peak of the traveling wave mutually canceled. Simulations by Sisto et al (2015) showed that increasing the bandwidth of cochlear filters leads to involvement of more basally placed perturbations on the BM in the SFOAE generation Another explanation is that the near-zero latency components are due to nonlinear reflection. The effect of a highfrequency suppressor on the SFOAE residual was shown in

Methods

Discussion

Conclusion