Can Noise-Induced Temporary Threshold Shift Cause Persistent Impairment of Speech Understanding?

Details

• Personal Author:
  Brammer, A. J. ; Cherniack, Martin G. ; Cienkowski K ; Grady J ; Parham K ; Yu G
• Description:
  After engaging in noisy hobbies or listening to loud music, it is common for persons to experience a temporary change in their hearing, feeling for a time that their ears are "muffled", or sensing they are in unusually quiet surroundings, or having to increase the volume of their radio, TV, or music player. These symptoms of temporary changes in the threshold of hearing are commonly called temporary threshold shifts (TTS). Recent animal experiments have found that exposure to sufficient noise to produce a temporary change in the threshold of hearing unexpectedly caused persistent suprathreshold changes in auditory function, even though the long-term hearing thresholds remained normal. The results conflict with current occupational noise exposure guidelines and regulations, which assume reversible, temporary threshold shifts (TTS) are associated with benign levels of noise exposure, but instead suggest they may mask an underlying neuropathology with consequences for auditory processing in humans. In view of the animal findings, we have studied the hearing of a population of 451 university students, many of whom reported symptoms characteristic of TTS, or had engaged in hobbies and activities involving exposure to noise or loud music. We found statistically significant relationships between deteriorating speech understanding and increasing reports of TTS-like symptoms, the performance of noisy hobbies and activities, and use of personal music players. Similar responses were obtained from a subset of 46 students from the population with normal audiometric hearing thresholds. When the 46 students were formed into groups experiencing TTS-like symptoms, or exposure to noise or music, and groups not so "exposed" with closely-matched mean audiometric hearing thresholds, neither the TTS-like symptom group nor noise-exposed groups possessed mean word scores that differed statistically from those of their respective control groups in a psychoacoustic test of speech intelligibility in noise. The discrepancy between questionnaire responses and objective word scores remains unexplained but may reflect the large differences in performance between individuals, which could mask subtle changes in intelligibility between groups. It may also be a consequence of the test environment (using headphones), which did not reflect the situations in which the problems were reported (i.e., rooms with many people talking). In contrast, a statistically significant deterioration was found in the group of students who reported TTS-like symptoms compared to controls in a sensitive test of hearing function, the detection of a warbling sound (or amplitude modulation detection). To our knowledge, this is the first time a persistent hearing defect has been detected in healthy humans with closely-matched normal hearing thresholds who have experienced TTS-like symptoms, and confirms the concerns raised by the animal experiments. With such a large number of students reporting substantial interference understanding speech in common situations involving competing sounds or talkers, there is clearly a need for further studies to clarify the extent and impact of this unexpected "hidden" hearing loss on a broader population, and on the need for public policy changes concerning what constitutes acceptable occupational and environmental noise exposures. It is apparent that audiometric threshold sensitivity may not fully reflect neural degeneration in the ears and so, contrary to current practice and regulation, may not be the most suitable metric for assessing auditory deficits caused by the damaging effects of noise. [Description provided by NIOSH]
• Subjects:
  Environmental Exposure Hearing Hearing Loss Nervous System Noise Noise, Occupational Occupational Health Safety
• Keywords:
  Audiometry Auditory Perception Auditory System Exposure Levels Hearing Impairment Hearing Level Hearing Threshold Neuropathology Noise Exposure Speech Disorders Threshold Shift

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• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  Connecticut ; OSHA Region 1
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-44
• NIOSHTIC Number:
  nn:20052938
• NTIS Accession Number:
  PB2019-100117
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R21-OH-010365, 2016 May; :1-44
• Contact Point Address:
  Dr. Anthony J. Brammer, Department of Medicine, University of Connecticut Health, 263 Farmington Avenue, Farmington CT 06030
• Email:
  brammer@uchc.edu
• Federal Fiscal Year:
  2016
• Performing Organization:
  University of Connecticut School of Medicine, Farmington
• Peer Reviewed:
  False
• Start Date:
  20130901
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20160228
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:85ffc03dc6adb25380bdca230784c549fb08b064977e53e417055e2de19b4f52a3230d2a38cbb8cc7dc4739adb385fe6023ec9508b1f3028f6ca9c601c374eff
• Download URL:
  https://stacks.cdc.gov/view/cdc/218732/cdc_218732_DS1.pdf
• File Type:
  [PDF - 1.86 MB ]