Recording active basilar membrane tuning characteristics using distortion-product otoacoustic emissions

The objective of this study was to describe ways in which properties of human cochlear travelling waves may be manifested in characteristics of distortion-product otoacoustic emissions (DPOAEs). Four young adults served as subjects. DPOAE magnitude was studied for various frequency-ratio and intensity relationships of the primary stimuli. Results revealed complex relationships between stimulus level (L) and frequency ratios (f). The optimal f2/f1 ratios were highly dependent upon differences between L1 and L2. Maximum distortion product amplitudes were encountered when L2 was smaller than L1 for several stimulus conditions and when f2/f1 ratios were approximately 1.20 (range = 1.05 to 1.25). These observations replicate and extend the findings of prior investigations regarding the optimal parameters associated with the production of DPOAEs, and also provide evidence of the complex, nonlinear events leading to the creation of DPOAEs