Effects of speech intelligibility in ecological noise on contralateral suppression of otoacoustic emissions

Some individuals experience difficulty understanding speech, especially in noisy environments, despite having normal hearing thresholds in audiometry. The ability to selectively focus on a particular sound in such environments is believed to be mediated by the cochlear efferent system, specifically the medial olivocochlear reflex (MOCR). To non-invasively evaluate MOCR, contralateral suppression of otoacoustic emissions (CSOAEs) has been studied. OAEs are sounds generated by the active cochlea and emitted toward the ear canal. However, most previous studies used artificial stimuli (e.g., white or pink noise) as contralateral stimuli and have largely overlooked the effects of selective attention. In this study, the relationship between CSOAE and speech perception in noise was investigated using more ecologically valid contralateral stimuli, such as recorded speech (e.g., newspaper reading) combined with everyday background noise (e.g., dishwashing sounds). Influences of selective attention were also investigated by processing the voice to unintelligible. Results showed that the magnitude of suppression was influenced more by the frequency characteristics of the contralateral stimuli than by their overall sound pressure level (dB LAeq). These findings may contribute to the development of improved assessment tools for individuals with normal hearing but difficulties in speech comprehension.