High-frequency hearing influences lower-frequency distortion-product otoacoustic emissions

Objectives: The primary goal of this study was to test the ability of 2f(1) -f(2) distortion-product otoacoustic emissions (DPOAEs) to detect reduced c ochlear function in the presence of normal behavioral sensitivity. Design: A prospective study was performed in normal-hearing young adults us ing simple and complex regression analyses to clarify the relationship betw een ultrahigh frequency (UHF) hearing and DPOAE levels at lower frequencies , as well as the influence of hearing levels for frequencies within the con ventional test range and subject age on this association. Methods: Average DPOAE levels between 4 to 8 kHz, which were elicited by eq uilevel primary tones of low to moderate levels, were measured as level-fre quency functions, or distortion-product (DP) grams, and related to the mean UHF hearing levels from 11.2 to 20 kHz. The median hearing level for the U HF hearing was used to separate subjects into good and poor UHF hearers. Th is distinction was then used to compare DPOAE levels from 4 to 8 kHz for th e 2 groups to determine if UHF hearing status influenced DPOAE levels at lo wer frequencies. Results: Simple regression analysis revealed that the 4- to 8-kHz DPOAE lev els were significantly correlated with the pure-tone average (PTA) from 11. 2 to 20 kHz. However, the PTA for 4 and 8 kHz was also significantly correl ated with the PTA for UHF hearing. Further multiple regression analyses rev ealed that UHF hearing significantly and uniquely accounted for approximate ly 14% of the variance in DPOAE levels from 4 to El kHz for most of the pri mary-tone level combinations. In contrast, neither the PTA for the conventi onal hearing range nor subject age contributed significantly to the DPOAE v ariance. Conclusions: The findings suggest that UHF hearing influences DPOAEs at sig nificantly lower frequencies because emissions are sensitive to subtle chan ges in outer hair cells not yet detected by pure-tone thresholds in this re gion or because alterations in the basal cochlea affect the generation of l ower-frequency DPOAEs originating from more apical cochlear regions.