Pure-tone threshold estimation from extrapolated distortion product otoacoustic emission I/O-functions in normal and cochlear hearing loss ears

A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f(1)-f(2) distortion products and pure-tone threshold at f(2) were measured at 51 frequencies between f(2) = 500 Hz and 8 kHz at up to ten primary tone levels between L-2 = 65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss cars. Using an optimized primary tone level setting (L-1 = 0.4L(2) + 39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f(2), the pressure of the 2 f(1) - f(2) distortion product p(DP) is a linear function of the primary tone level L-2 Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and unpaired hearing, This suggests that the observed linear functional dependency is quite general. Extrapolating towards p(DP)=0 yields the DPOAE threshold for L-2 There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of all essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data. (C) 2002 Acoustical Society of America.