Relations between measures of speech-in-noise performance and measures of efferent activity

Individual differences in auditory perceptual abilities in noise are well documented, but the factors causing such variability are unclear. The purpose of this study was to determine if individual differences in responses measured from the auditory efferent system were correlated with individual variations in speech-in-noise performance. The relation between behavioral performance on three speech-in-noise tasks and two objective measures of the efferent auditory system were examined in thirty normal-hearing, young adults. Two of the speech-in-noise tasks measured an acceptable noise level (ANL), the maximum level of speech babble noise that a subject is willing to accept while listening to a story. ANL was determined for both monotic (story and noise in the same ear) and a dichotic condition (story and noise in opposite ears). The third speech-in-noise task evaluated speech recognition using monosyllabic words presented in competing speech babble. Auditory efferent activity was assessed by examining the resulting suppression of click-evoked otoacoustic emissions (CEOAEs) following the introduction of contralateral, broadband noise (BBN). The activity levels of the ipsilateral and contralateral acoustic reflex (AR) arcs were evaluated using pure-tones and BBN. Results showed significant correlations (p < 0.01) between: (1) the contralateral AR Ts to BBN and contralateral suppression of CEOAEs, and (2) the monotic ANL (ANLm) and dichotic ANL (ANLd). Significant correlations (p < 0.05) were also found between: (1) the monotic (right ear) speech recognition-in-babble task and the right, ipsilateral acoustic reflex threshold (ART), and (2) the dichotic ANL (ANLd) and the phoneme recognition-in-noise (PRnx).