Effects of hidden hearing loss on the representation of speech-in-noise in the gerbil auditory midbrain

Increasing evidence indicates that noise exposure selectively damages high-threshold auditory nerve fibres, in the absence of damage to sensory hair cells. This “hidden hearing loss (HHL)"—undetected by conventional tests such as audiometry—is suggested to account for undiagnosed difficulties processing speech in background noise. Here, we demonstrate in the midbrain of gerbils exposed to a single, controlled noise insult, and in human listeners, evidence of increased neural gain in the central auditory pathways, indicative of damage to high-threshold ANFs following noise exposure. Neural responses were higher, and discrimination performance for 60-dB SPL “vowel-consonant-vowel” stimulus (VCVs in background noise (speech-shaped, + 12 to -12 dB signal-to-noise ratio) enhanced, in noise-exposed animals compared to controls. Conversely, for 75-dB SPL VCVs, neural discrimination was better in control, compared to noise-exposed, animals. A similar pattern was evident in human listeners, and was positively corr...