Theoretical study on onset of cubic distortion product otoacoustic emissions Free

The distortion product otoacoustic emissions (DPOAEs) are generated when the cochlea is stimulated by two pure tones with different frequencies f₁ and f₂. Onset of the DPOAE amplitude may have a nonmonotonic complex shape when the f₂ is pulsed during a stationary f₁ input. Observed complexities have been explained as (1) due to the secondary source of the DPOAE at the distortion product (DP) characteristic site, and (2) due to the spatial distribution of DP sources with different phases. There is also a third possibility that the complexities are due to the suppression of the f₁ basilar membrane (BM) response during the f₂ onset. In this study, a hydrodynamic cochlea model is used to examine influence of f₁ suppression on the time course of DPOAE onset. In particular, a set of simulations was performed for frequency ratio f₂/f₁ = 1.26 and various levels of the primary tones (L₁ and L₂=30-70 dB SPL) to determine the relationship between time dependencies of the DPOAE onset and the suppression of the f₁ BM response. The model predicts that suppression of the f₁ BM response can cause suppression of DPOAE amplitude during the onset period.