Restoration of audibility through frequency-specific amplification is central to the clinical management of sensorineural hearing loss (SNHL). Yet, patients often struggle to understand audible speech, especially in noisy environments. These suprathreshold deficits are conventionally attributed to reduced frequency selectivity and to non-peripheral factors. However, our cross-species studies show that damage to cochlear hair cells not only broadens auditory filter “tips” as previously recognized, but can also distort the fundamental tonotopy of the cochlea such that the temporal responses of the base are commandeered by “off-frequency” (i.e., low-frequency) sound fluctuations through overzealous filter “tails.” This effect is especially pronounced with naturalistic stimuli and background noise possessing pink-like spectra, which contain intense low-frequency components alongside softer but informative higher-frequency content. In a chinchilla model of SNHL with noise-induced permanent threshold shifts, single-unit auditory-nerve measurements revealed that hypersensitive tuning-curve tails were the dominant driver of degraded speech envelope coding, even with sound amplifier gains akin to modern hearing aids. In parallel human studies, individuals with mild or moderate SNHL showed hypersensitive tuning-curve tails linked to impaired speech envelope tracking as measured through electroencephalography. Crucially, individual differences in the estimated degree of distorted tonotopy predicted aided speech-in-noise outcomes.
Bharadwaj et al. (Tue,) studied this question.