Otoacoustic Emissions Evoked by the Time-Varying Harmonic Structure of Speech

Abstract

The human auditory system is exceptional at comprehending an individual speaker even in complex acoustic environments. Because the inner ear, or cochlea, possesses an active mechanism that can be controlled by subsequent neural processing centers through descending nerve fibers, it may already contribute to speech processing. The cochlear activity can be assessed by recording otoacoustic emissions (OAEs), but employing these emissions to assess speech processing in the cochlea is obstructed by the complexity of natural speech. Here we develop a novel methodology to measure otoacoustic emissions that are related to the time-varying harmonic structure of speech (speech-DPOAEs). We then employ the method to investigate the effect of selective attention on the speech-DPOAEs. We provide tentative evidence that the speech-DPOAEs are larger when the corresponding speech signal is attended than when it is ignored. Our development of speech-DPOAEs opens up a path to further investigations of the contribution of the cochlea to the processing of complex real-world signals. Significance Statement Real-world environments, such as a loud pub or restaurant, are often noisy. The detection of sound occurs in the inner ear, which also possesses an active mechanism to mechanically amplify sound vibrations. Because the active mechanism can be regulated by the nervous system, it may already play a part in analyzing complex acoustic scenes. However, investigations of these questions have been hindered by a lack of experimental tools to assess the inner ear's activity in relation to speech processing. Here we develop a method to record otoacoustic emissions that relate to the harmonic structure of speech, a key feature of many speech parts. We use the novel tool to provide tentative evidence that the inner ear contributes to selective attention.