Alternative distortion product otoacoustic emissions and hearing loss in a clinical population

Parameters of the alternative distortion product otoacoustic emissions (DPOAEs) 4f1-3f2, 3fl-2f2, 2f2-f1, 3f2-2f1 and 4f2-3f1 as well as the cubic distortion product 2f1-f2 were extracted from the ILO 92 binary files of patients reported on earlier (Lind, 1998). The DPOAEs were recorded at 18 stimulus levels between 19 and 70 dB SPL. The prevalence of at least one valid DPOAE data-point varied from 74% at 4f1-3f2 to 100% at 2f2-f1. The mean number of valid points was six for 2f2-f1, but generally below four for the others. The mean maximum amplitude for the alternative DPOAEs was 6-12 dB below that of the 2f1-f2. The mean maximum signal-to-noise-ratio (SNR) was between 2.5 and 3.5 dB SPL for the four most peripheral emissions and increased to 6.7 dB SPL for the 2f2-f1. As reported earlier, the 2f1-f2 distortion was fairly well correlated with hearing threshold at 2 kHz. The 2f2-f1 shows some correlation with hearing loss at frequencies above f2, but the other DPOAEs were not correlated with hearing loss at any frequency, which may suggest different generating mechanisms and/or sites. The influence of age on maximum amplitude was small but significant for all DPOAEs.