Effects of age on speech understanding in normal hearing listeners: Relationship between the auditory efferent system and speech intelligibility in noise
Human listeners are able to listen to one voice in the midst of other conversations and background noise. Although the neural mechanisms for this process are not well understood, there is growing evidence that the medial olivocochlear (MOC) auditory efferent system located in the brainstem is involved in the detection of signals in noise, such as speech sounds, by modulating cochlear (inner ear) active physiological mechanisms. The present study examined MOC efferent (feedback) effects as revealed in distortion product otoacoustic emissions (DPOAEs) and effects of spatial separation for speech perception in background noise. Both spatial separation of speech in noise and contralateral suppression (CS) of DPOAE invoke neural mechanisms central to the inner ear. We sought to determine whether these tasks might be related and thereby represent involvement in the ability to listen to one voice in the midst of concurrent conversation and background noise; a situation in which elderly listeners have great difficulty. The Hearing in the Noise Test (HINT) [Nilsson, M., Soli, S.D., Sullivan, J.A., 1994. Development of the hearing in noise test for the measurement of speech reception thresholds in quiet and in noise. J. Acoust. Soc. Amer. 95, 10851099] was used to obtain release from masking (RFM) estimates of speech in noise. DPOAEs were used to measure effects of broadband noise introduced to the ear contralateral to the target ear (CS). Significant age effects were found in both domains. Significant correlations resulted between speech perception in noise (RFM) and the degree of CS of DPOAEs. RFM was significantly related only to age and CS at the DPOAE narrow-band frequency of 12kHz; a frequency band critical for successful speech perception. These findings suggest that the MOC efferent system and neural mechanisms underlying RFM are related and contribute to sound source determination commonly referred to as the cocktail party effect.
aging release from masking cocktail party effect presbycusis medial efferent system