No association between idiopathic hidden hearing loss and behavioral adaptation to noise in humans

Adaptation to noise refers to the improvement in word-in-noise recognition as words are delayed a few hundred milliseconds in the noise. This adaptation is thought to reflect adjustments of the dynamic range of auditory neurons to the most frequent noise level. Evidence from a mouse model suggests that hidden hearing loss (HHL), a diminished auditory nerve response without a hearing loss, selectively impairs neural dynamic range adaptation to loud sound environments. The aim of the present study was to investigate whether HHL is associated with poor behavioral adaptation to loud noise in speech recognition. For 89 people (aged 19-86 years) with clinically normal hearing, we measured speech reception thresholds (SRTs; signal-to-noise ratios at 50 % recognition) for disyllabic words in stationary, speech-shaped noise. SRTs were measured for words delayed 50 and 800 ms in the noise and for noise levels of 55 and 78 dB SPL. Adaptation was calculated as the SRT improvement in the long-delay relative to the short-delay condition. Because adaptation is greater for vocoded than for natural words, words were processed through a tone vocoder. The response of the auditory nerve was assessed using the amplitude of the auditory brainstem response (ABR) wave I and the rate of growth (slope) of the wave I amplitude with increasing stimulus level. Adaptation occurred at the two noise levels but was greater for the louder noise than for the softer noise (2.3 dB vs 1.3 dB, respectively). This happened because SRTs were worse for the louder noise in the short but not in the long delay condition. The large variability in ABR wave I amplitude (0.10 to 0.54 μV) and slope (-0.004 to 0.023 μV/dB) suggested that the sample included participants with varying degrees of HHL of uncertain etiology (idiopathic). However, adaptation was not correlated with the wave I amplitude or slope, even after accounting for the potential confounding effect of elevated hearing thresholds in an extended frequency range. Findings suggest that adaptation to noise in speech recognition is greater at higher noise levels but provide no evidence that idiopathic HHL leads to reduced adaptation to noise in humans.