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Cochlear toughening, protection, and potentiation of noise-induced trauma by non-Gaussian noise.

Authors
Hamernik-RP; Qui-W; Davis-B
Source
J Acoust Soc Am 2003 Feb; 113(2):969-976
NIOSHTIC No.
20029181
Abstract
An interrupted noise exposure of sufficient intensity, presented on a daily repeating cycle, produces a threshold shift (TS) following the first day of exposure. TSs measured on subsequent days of the exposure sequence have been shown to decrease relative to the initial TS. This reduction of TS, despite the continuing daily exposure regime, has been called a cochlear toughening effect and the exposures referred to as toughening exposures. Four groups of chinchillas were exposed to one of four different noises presented on an interrupted (6 h/day for 20 days) or noninterrupted (24 h/day for 5 days) schedule. The exposures had equivalent total energy, an overall level of 100 dB(A) SPL, and approximately the same flat, broadband long-term spectrum. The noises differed primarily in their temporal structures; two were Gaussian and two were non-Gausssian, nonstationary. Brainstem auditory evoked potentials were used to estimate hearing thresholds and surface preparation histology was used to determine sensory cell loss. The experimental results presented here show that: (1) Exposures to interrupted high-level, non-Gaussian signals produce a toughening effect comparable to that produced by an equivalent interrupted Gaussian noise. (2) Toughening, whether produced by Gaussian or non-Gaussian noise, results in reduced trauma compared to the equivalent uninterrupted noise, and (3) that both continuous and interrupted non-Gaussian exposures produce more trauma than do energy and spectrally equivalent Gaussian noises. Over the course of the 20-day exposure, the pattern of TS following each day's exposure could exhibit a variety of configurations. These results do not support the equal energy hypothesis as a unifying principal for estimating the potential of a noise exposure to produce hearing loss.
Keywords
Noise-induced-hearing-loss; Noise-exposure; Hearing-threshold; Exposure-levels; Animals; Animal-studies; Histology; Exposure-assessment; Hearing-loss; Auditory-system; Audiometry
Contact
Auditory Research Laboratory, State University of New York, 107 Beaumont Hall, Plattsburgh, New York 12901, USA
CODEN
JASMAN
Publication Date
20030201
Document Type
Journal Article
Email Address
roger.hamernik@plattsburgh.edu
Funding Amount
2829511
Funding Type
Grant
Fiscal Year
2003
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-002317
Issue of Publication
2
ISSN
0001-4966
Source Name
Journal of the Acoustical Society of America
State
NY
Performing Organization
State University of New York at Buffalo, Buffalo, New York
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