Depth matters - Towards finding an objective neurophysiological measure of behavioral amplitude modulation detection based on neural threshold determination

With increasing numbers undergoing intervention for hearing impairment at a young age, the clinical need for objective assessment tools of auditory discrimination abilities is growing. Amplitude modulation (AM) sensitivity has been known to be an important factor for speech recognition particularly among cochlear implant (CI) users. It therefore would be useful to develop objective measures of AM detection for future clinical assessment of CI users; this study aimed to verify the feasibility of a neurophysiological approach studying a cohort of normal-hearing participants. The mismatch waveform (MMW) was evaluated as a potential objective measure of AM detection for a low modulation rate (8 Hz). This study also explored the relationship between behavioral AM detection and speech-in-noise recognition. The following measures were obtained for 15 young adults with no known hearing impairment: (1) psychoacoustic sinusoidal AM detection ability for a modulation rate of 8 Hz; (2) neural AM detection thresholds estimated from morphology weighted cortical auditory evoked potentials elicited to various AM depths; and (3) AzBio sentence scores for speech-in-noise recognition. No significant correlations were found between speech recognition and behavioral AM detection measures. Individual neural thresholds were obtained from MMW data and showed significant positive correlations with behavioral AM detection thresholds. Neural thresholds estimated from morphology weighted MMWs provide a novel, objective approach for assessing low-rate AM detection. The findings of this study encourage the continued investigation of the MMW as a neural correlate of low-rate AM detection in larger normal-hearing cohorts and subsequently in clinical cohorts such as cochlear implant users.