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Auditory Temporal Processing and its Disorders$
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Jos J. Eggermont

Print publication date: 2015

Print ISBN-13: 9780198719090

Published to Oxford Scholarship Online: May 2015

DOI: 10.1093/acprof:oso/9780198719090.001.0001

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Hearing loss and temporal processing

Hearing loss and temporal processing

Chapter:
(p.215) Chapter 12 Hearing loss and temporal processing
Source:
Auditory Temporal Processing and its Disorders
Author(s):

Jos Eggerrmont

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198719090.003.0012

Hearing loss implies more than just a loss of sensitivity as expressed in the audiogram. Yet, this is not always appreciated. As in aging, auditory pathology that is not reflected in increased hearing thresholds may add to temporal processing deficits. Animal experiments have shown that non-traumatic noise exposure at a young age may cause degeneration of auditory nerve fibers in old age. The pathology reflects changes in inner hair cell ribbon synapses as a result of lifelong exposure to non-traumatic noise. These fibers are likely the ones with high threshold and their loss therefore is not reflected in the audiogram. Animal auditory cortex studies have also shown that noise-induced hearing loss leads to deterioration in gap detection and voice-onset-time representation. Changes also occurred in the temporal modulation transfer functions, namely a slight reduction in the upper repetition rate limit of coding for click trains. In contrast, and surprisingly a considerable enhancement in the upper limit of modulation frequency representation as well as the strength of the tMTFs for amplitude modulated noise. The latter can be explained by a homeostatic increase in central synaptic efficacy as a result of the hearing loss. However, even in auditory nerve fibers the strength of envelope coding was enhanced after noise exposure. In human imaging studies it was found that even moderate declines in peripheral auditory acuity may lead to a systematic downregulation of neural activity during the processing of higher-level aspects of speech, and may also contribute to loss of gray matter volume in primary auditory cortex.

Keywords:   ribbon synapses, delayed degeneration of nerve fibers, gap detection, temporal modulation transfer function, brain imaging, animal, human

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