Abstract
Listeners with hearing loss have difficulty processing sounds in noisy environments. This is most noticeable for speech perception, but is reflected in a basic auditory processing task: detecting a tonal signal in a noise background, i.e., simultaneous masking. It is unresolved whether the mechanisms underlying simultaneous masking arise from the auditory periphery or from the central auditory system. Poor detection in listeners with sensorineural hearing loss (SNHL) is attributed to cochlear hair cell damage. However, hearing loss alters neural processing in the central auditory system. Additionally, both psychophysical and neurophysiological data from normally hearing and impaired listeners suggest that there are additional contributions to simultaneous masking that arise centrally. With SNHL, it is difficult to separate peripheral from central contributions to signal detection deficits. We have thus excluded peripheral contributions by using an animal model of early conductive hearing loss (CHL) that provides auditory deprivation but does not induce cochlear damage. When tested as adults, animals raised with CHL had increased thresholds for detecting tones in simultaneous noise. Furthermore, intracellular in vivo recordings in control animals revealed a cortical correlate of simultaneous masking: local cortical processing reduced tone-evoked responses in the presence of noise. This raises the possibility that altered cortical responses which occur with early CHL can influence even simple signal detection in noise.
Highlights
Listeners with hearing loss often struggle to understand speech in noisy environments
DEVELOPMENTAL CONDUCTIVE HEARING LOSS DEGRADES SIGNAL DETECTION IN NOISE Behavioral thresholds for signal detection in noise were obtained from two groups of adult gerbils: animals reared with conductive hearing loss (CHL) prior to hearing onset, and age-matched controls (CTR)
This study demonstrates that simultaneous masking involves the central auditory system and is impaired by early CHL
Summary
Listeners with hearing loss often struggle to understand speech in noisy environments This difficulty is reflected in increased thresholds for detecting a simple signal in noise, i.e., simultaneous masking. Chronic middle ear infections (otitis media) produce a fluctuating CHL that can overlap with critical periods of neural development Auditory deprivation during these periods alters intrinsic cellular and synaptic properties throughout the central auditory system (Vale and Sanes, 2000, 2002; Leao et al, 2004; Youssoufian et al, 2005; Leão et al, 2006). Developmental CHL is correlated with persistent perceptual problems that are presumably linked to changes in the central auditory system (Whitton and Polley, 2011). Binaural CHL leads to increased perceptual detection thresholds for slow amplitude modulations, and these behavioral deficits match the magnitude of neural shifts in auditory cortex (ACx; Rosen et al, 2012)
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