Abstract

Verbal communication in noisy backgrounds is challenging. Understanding speech in background noise that fluctuates in intensity over time is particularly difficult for hearing-impaired listeners with a sensorineural hearing loss (SNHL). The reduction in fast-acting cochlear compression associated with SNHL exaggerates the perceived fluctuations in intensity in amplitude-modulated sounds. SNHL-induced changes in the coding of amplitude-modulated sounds may have a detrimental effect on the ability of SNHL listeners to understand speech in the presence of modulated background noise. To date, direct evidence for a link between magnified envelope coding and deficits in speech identification in modulated noise has been absent. Here, magnetoencephalography was used to quantify the effects of SNHL on phase locking to the temporal envelope of modulated noise (envelope coding) in human auditory cortex. Our results show that SNHL enhances the amplitude of envelope coding in posteromedial auditory cortex, whereas it enhances the fidelity of envelope coding in posteromedial and posterolateral auditory cortex. This dissociation was more evident in the right hemisphere, demonstrating functional lateralization in enhanced envelope coding in SNHL listeners. However, enhanced envelope coding was not perceptually beneficial. Our results also show that both hearing thresholds and, to a lesser extent, magnified cortical envelope coding in left posteromedial auditory cortex predict speech identification in modulated background noise. We propose a framework in which magnified envelope coding in posteromedial auditory cortex disrupts the segregation of speech from background noise, leading to deficits in speech perception in modulated background noise.SIGNIFICANCE STATEMENT People with hearing loss struggle to follow conversations in noisy environments. Background noise that fluctuates in intensity over time poses a particular challenge. Using magnetoencephalography, we demonstrate anatomically distinct cortical representations of modulated noise in normal-hearing and hearing-impaired listeners. This work provides the first link among hearing thresholds, the amplitude of cortical representations of modulated sounds, and the ability to understand speech in modulated background noise. In light of previous work, we propose that magnified cortical representations of modulated sounds disrupt the separation of speech from modulated background noise in auditory cortex.

Highlights

  • IntroductionHearing loss is a major health issue that affects Ͼ40% of the population who are 60 years of age or older (Agrawal et al, 2008)

  • Hearing loss is a major health issue that affects Ͼ40% of the population who are 60 years of age or older (Agrawal et al, 2008).Received Aug. 29, 2016; revised May 9, 2017; accepted May 23, 2017

  • Our results show that both hearing thresholds and, to a lesser extent, magnified cortical envelope coding in left posteromedial auditory cortex predict speech identification in modulated background noise

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Summary

Introduction

Hearing loss is a major health issue that affects Ͼ40% of the population who are 60 years of age or older (Agrawal et al, 2008). Received Aug. 29, 2016; revised May 9, 2017; accepted May 23, 2017. The most common form of hearing loss, sensorineural hearing loss (SNHL), is associated with damage to the hair cells in the cochlea. In addition to elevating audiometric thresholds, SNHL alters the perception and neural representations of sounds. The reduction in fast-acting compression associated with outer hair cell dysfunction exaggerates the perceived fluctuations in the amplitude of modulated sounds (Moore et al, 1996). Magnified neural coding of the temporal envelope of modulated sounds may not be beneficial for real-world

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