Distortion product otoacoustic emission (DPOAE) input/output functions and the influence of the second DPOAE source

Distortion product otoacoustic emissions (DPOAEs) at 2f(1) - f(2) (f(2)/f(1) = 1.2) have two components from different cochlear sources, i.e., a distortion component generated near f2 and a reflection component from the characteristic site of f(DP). The interaction of the two sources may negatively affect the DPOAE input/output (I/O) functions that are used to predict either auditory thresholds or the compression characteristics of the basilar membrane. This study investigates the influence of the reflection component on DPOAE I/O functions in a frequency range for f(2) from 1500 to 4500 Hz in steps of 18 Hz. A time windowing procedure is used to separate the components from the two DPOAE sources. With decreasing stimulus level, the relative contribution of the reflection component increases. I/O functions from the separated distortion component (DCOAE I/O functions) only show smooth changes in shape and slope with frequency, while "standard" DPOAE I/O functions show rapid changes between adjacent frequencies, indicating a strong influence from the interference with the second DPOAE source. A reduced variability for adjacent frequencies can be seen as well for prediction of hearing thresholds, when using DCOAE instead of DPOAE I/O functions. (C) 2004 Acoustical Society of America.