Relationship among speech perception in noise, auditory inhibitory measures and working memory in neurotypical adults

Successful speech perception in noise likely involves inhibition of the background noise in order to improve the signal-to-noise ratio, and thereby, the perception. However, the nature and extent of the contributions of the inhibitory mechanisms to speech perception in noise and the interactions among them are currently unclear. The current study investigated the contribution of auditory inhibitory measures mediated by olivocochlear and cortico-cortical processes and working memory (closely associated with cognitive inhibition) on speech perception in noise using structural equation models. For this purpose, a group of 72 neurotypical adults over a wide age range (20-65 years) who were homogenous in terms of their socioeconomic and educational status and quality of life were recruited. The results revealed a strong and significant association between speech perception in noise and the working memory capacity. The brainstem inhibitory measure - the medial olivocochlear reflex - also contributed to speech perception in noise. There was no evidence of a direct contribution by the cortico-cortical inhibitory measures (auditory sensory gating and context-dependent cortical encoding of speech) on speech perception in noise. However, the auditory brainstem and cortico-cortical processes demonstrated a trend of an inverse relationship. An additional finding was that age significantly influenced working memory but not speech perception in noise. Overall, the study demonstrated the relationships among the different inhibitory mechanisms and their contributions to speech perception in noise. It was found that individuals with higher working memory capacity and higher strength of the medial olivocochlear reflex had better speech perception in noise. The findings suggest potential considerations for refining rehabilitation protocols for speech perception in noise deficits and pave path for future studies, which may be conducted using ecologically more valid stimulus paradigms.