Speech detection: from the biomechanics of the apical cochlea to the auditory brainstem and cortex Seminar

One of the most common complaints of people with hearing impairment is a difficulty with understanding speech, in particular in challenging listening situations such as background noise. However, our understanding of how speech sounds are detected in the inner ear, the auditory brainstem and the cortex remains insufficient. Indeed, while the biomechanics of the inner ear at high frequencies has been greatly investigated, the cochlear region that is responsible for detecting the frequencies below 4 kHz that matter most for speech remains poorly understood. Moreover, the role of efferent connections from the auditory cortex to the brainstem and the inner ear for speech processing remains unclear. Here I present recent results that shed new light on these issues. Through laser-interferometric experiments and mathematical modelling my collaborators and I have shown that the apical organ of Cort can function as an elctromechanical transistor. This opens a potential route for efferent nerve fibers to sensitively regulate hearing sensitivity. Such efferent regulation may matter for detecting speech in background noise: my group has developed a mathematical technique to measure the response of the auditory brainstem to running, non-repetitive speech. We have employed this technique to show that the brainstem's response to speech is modulated by selective attention to one of two competing speakers. I conclude by discussing ongoing research regarding the role of cortical oscillations in speech processing and hearing impairment.