Aging, speech understanding in noise, and efferent suppression

Older adults often complain of difficulty understanding speech in the presence of background noise. Many times this difficulty occurs with aging even in the absence of hearing loss. The mediolivocochlear (MOC) efferent system has been implicated as a possible cause of this deficit because the MOC mediates outer hair cell function and may serve to suppress background noise. This research examined the relationship between speech understanding in noise, as measured by the Quick Speech in Noise (Quick SIN) Test and MOC function, as measured by contralateral suppression of distortion product otoacoustic emissions (DPOAEs) at F2 frequencies of 1, 2, and 4 kHz. Performance on these measures was assessed for gender and age with three groups of normal hearing adults (n = 36); young adults ranged in age from 19–29 years, middle-aged adults ranged in age from 40–51 years, and older adults ranged in age from 60–82 years of age. Quick SIN results showed that males' performance was superior to females' and that the middle-aged adults' performance was significantly better than the younger adults', but not the older adults'. Performance on the DPOAE suppression measure was not significant for differences in gender or age; but was significant for frequency (e.g., significant difference was noted between 2 and 4 kHz, but no difference was noted between 1 and 4 kHz or 1 and 2 kHz). The correlation of Quick SIN and DPOAE suppression for gender and each age group was performed. There was no relationship found between suppression frequency and Quick SIN scores for gender or age (e.g., young, middle, or older). However, when Quick SIN performance was collapsed across all groups and gender, a significant relationship was found between the speech-in-noise performance and 2 kHz suppression. Results indicated that neither efferent suppression nor speech understanding in noise was affected by aging. Results of the current study are not consistent with previous research findings; nevertheless, this investigation did show that speech-in-noise performance has a moderately strong relationship with contralateral efferent suppression regardless of age or gender.