Contralateral suppression of transient evoked otoacoustic emissions for various noise signals

Abstract

Purpose: Efferent auditory system has an inhibitory function in the auditory system, and has been hypothesized to improve speech perception in noise. The function of efferent auditory system can be measured non-invasively using suppression of otoacoustic emissions (OAEs). OAEs are very small amplitude sounds generated in the cochlea by motile function of outer hair cells, and activation of the efferent system reduces the amplitude of OAEs, referred as suppression of OAEs. Several studies have been carried out by various investigators to understand the role of efferent auditory pathways during auditory processing. These investigations have used white noise, narrowband noise, pure-tones, modulated tones, etc., to activate the efferent system. However, in real-life situation, these noises are seldom found, hence the findings of above investigations may not be readily generalized to real-life situations. Hence, the present study was carried out to investigate the effect of real-life noise signals on the suppression of OAEs.Method: A total of 19 young adults aged between 18 and 23 years participated in the study. Transient evoked otoacoustic emissions (TEOAEs) were recorded with and without suppressor signal in contralateral ear conditions. Suppressor signals included white noise, amplitude-modulated noise, and real-life noise signals. The amount of suppression elicited by these noise signals were measured and compared across the noise conditions.Results: Findings of present study shows the largest suppression of TEOAE for white noise. In contrast, speech babble elicited least suppression of TEOAE compared to other noise signals used in the present investigation. For amplitude-modulated noise, the amount of suppression increased with modulation frequency of noise. Among real-life noise signals, the suppression was largest for cafeteria noise compared with traffic noise.Conclusion: Real-life noise signals used in the present study also elicited suppression, but the amount of suppression was found to be variable depending on the type of noise.