Targeting coding deficits along the auditory pathway to better address speech-in- noise intelligibility problems: The case of cochlear synaptopathy
Résumé
An important challenge for our field lays in the understanding of the mechanisms involved in supra-threshold hearing, i.e. those that shape what we perceive and understand from our daily environment, and thus in the identification and characterization of their potential deficits. Current audiological measurements, assessing hearing sensitivity at threshold, are not appropriate to understand why many of us encounter significant problems understanding speech in the presence of other competitive talkers. Strikingly, it is estimated that over 10% of individuals with clinically-normal audiograms for their age report significant struggles with hearing in noise. In this talk, we will particularly focus on one source of coding deficit arising in the auditory nerve, first revealed in animal studies: “cochlear synaptopathy”, which corresponds to the loss of synapses connecting inner hair cells to auditory nerve fibers, i.e. the channels that convey the auditory signal to more central auditory stages. Animal studies have shown that this pathology naturally occurs with aging, but that it can also be induced by temporary exposure to intense noise. Critically, it can occur without damage to outer- hair cells, and therefore remain undetected by current measurements of audibility: it thus constitutes one form of “hidden hearing loss”, and is thought to be an important factor contributing to speech-in-noise understanding difficulties reported by humans. Yet, it remains unclear which non-invasive biomarkers could be used to assess the prevalence of this pathology in humans. Here, we will present psychophysical and electrophysiological measurements based on complex auditory stimuli with different spectral envelopes, specifically designed to characterize the impact of synaptopathy through coding fidelity to temporal fine- structure, which is known to be critical to speech-in-noise understanding. We will discuss how several markers extracted from these measurements can account for SPiN intelligibility differences measured within and across younger and older listeners, with/without outer-hair cell damage.