Investigation of relation between auditory efferent system and speech in noise performance in normal hearing individiuals

Objective: This study aims to investigate the relationship between speech in noise performance and auditory efferent system in normal hearing individuals with contralateral suppression of Distortion Product Otoacoustic Emission (DPOAE). Methods: The study included 61 individuals between the ages of 18-55 with normal otologic and audiological findings. Following the hearing and impedancemetric evaluations of the individuals, Speech In Noise (SIN) Test was applied. Next, DPOAE measurement without contralateral noise stimulation and suppression measurement of DPOAE using contralateral 50 dB SL white noise were carried out. DPOAE and contralateral suppression were measured in the 500-1000-1500-2000-3000-4000-5000 Hz frequency range. Results: According to DPOAE measurement results, it is concluded that the amplitudes in the 1000, 1500, 2000 Hz frequencies were statistically significantly higher in the right and left ear compared to other frequencies. When the contralateral suppression measurement results were evaluated, the amount of suppression obtained in the right ear in the 500 Hz frequency was found to be statistically significantly higher than the left ear. Suppression amounts did not show a significant difference according to frequencies. In the comparison of the DPOAE measurement results and contralateral suppression results between the genders, no significant difference was found between the two genders. In the right ear, as the hearing threshold increased at 250 Hz and 4000 Hz frequencies, it was observed that the SIN performance decreased. However, this was found to be a low level relationship. When the relationship between hearing thresholds and suppression amounts is analyzed, it was observed that the amount of suppression decreased as the hearing thresholds increased in the right and left ears. As the amount of suppression increases, SIN performance increases in direct proportion; this indicates statistically significant relationship in the right and left ear frequency at 1500 Hz. Conclusion: In this study, a correlation was found between the magnitude of suppression of contralateral otoacoustic emission and speech in noise performance. The results indicate that the medial olivocochlear system may help in understanding speech in noise and that efferent fibers may have a possible role in hearing. It has been concluded that as a result of the advancement of such researches, potential causes of the problem of understanding speech in noise, which is one of the difficulties experienced by normal hearing individuals, may be revealed and clinical treatments may be developed. Key Words: auditory efferent system, otoacoustic emission, contralateral suppression, understanding speech in noise, hearing