Contralateral suppression findings in individuals with poor speech perception in noise

This study aimed to compare contralateral suppression responses associated with the Medial Olivocochlear (MOC) reflex between individuals with high and low levels of speech perception in noise. The study was conducted with a total of 60 participants, including 50 females and 10 males. Initially, pure-tone audiometry and speech audiometry tests were administered to evaluate hearing thresholds and speech discrimination scores. Following this, the participants' speech perception performance in noise was assessed using the Hearing in Noise Test (HINT), and they were categorized accordingly. Subsequently, the MOC reflex was measured using a Transient Evoked Otoacoustic Emission (TEOAE)-based protocol with the ILO V6 292-II device. Suppression measurements were carried out at frequencies of 1 kHz, 1,4 kHz, 2 kHz, 2,8 kHz, and 4 kHz, using a 65 dB peSPL click stimulus and 50 dB SPL broadband noise delivered contralaterally. According to statistical analysis, significant differences in contralateral suppression levels between the groups were observed at 1,4 kHz and 2,8 kHz (Table 5, p<0,05). In these frequencies, individuals with higher speech-in-noise performance exhibited more pronounced suppression effects. A positive and statistically significant correlation was found between HINT scores and MOC reflex positivity at 1,4 kHz (r=0,330), 2 kHz (r=0,257), and 4 kHz (r=0,335) (Table 6, p<0,05). These results indicate a moderate correlation at 1,4 and 4 kHz, and a weak correlation at 2 kHz. No statistically significant correlations were found at the other frequencies (p>0,05). These findings suggest that the efferent auditory system may contribute to speech perception performance, particularly in the mid-to-high frequency range. Additionally, a weak but statistically significant positive correlation was observed between age and the MOC reflex at 2,8 kHz (r=0,264, p<0,05). In conclusion, the MOC reflex was found to be associated with speech perception in noise at specific frequencies, indicating that the functional integrity of the efferent auditory system may influence individual auditory performance. Contralateral suppression testing may serve as a useful tool in the clinical evaluation of individuals with normal hearing thresholds who report difficulty understanding speech in noisy environments. Keywords: medial olivocochlear reflex, hearing in noise test, efferent auditory system, speech perception in noise