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Frequency dependence and harmonic distortion of stapes displacement and intracochlear pressure in response to very high level sounds.
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- Additional Information
- Source:
Publisher: Elsevier/North-Holland Biomedical Press Country of Publication: Netherlands NLM ID: 7900445 Publication Model: Print-Electronic Cited Medium: Internet ISSN: 1878-5891 (Electronic) Linking ISSN: 03785955 NLM ISO Abbreviation: Hear Res Subsets: MEDLINE
- Publication Information:
Original Publication: Amsterdam, Elsevier/North-Holland Biomedical Press.
- Subject Terms:
- Abstract:
Previous reports have suggested that intracochlear pressures (P IC ) measured at the base of the cochlea increase directly proportionally with stapes displacement (D Stap ) in response to moderately high (<130 dB SPL) level sounds. Consistent with this assumption, we have reported that for low frequency sounds (<1 kHz), stapes displacement and intracochlear pressures increase linearly with sound pressure level (SPL) for moderately high levels (<130 dB SPL), but saturate at higher exposure levels (>130 dB SPL). However, the magnitudes of each response were found to be frequency dependent, thus the relationship between D Stap and P IC may vary at higher frequencies or higher levels. In order to further examine this frequency and level dependence, measurements of D Stap and P IC were made in cadaveric human temporal bones prepared with a mastoidectomy and extended facial recess to expose the ossicular chain. P IC was measured in scala vestibuli (P SV ) and scala tympani (P ST ) simultaneously with SPL in the external auditory canal (P EAC ) and laser Doppler vibrometry (LDV) measurements of stapes velocity (V Stap ). Consistent with prior reports, D Stap and P SV increased proportionally with sound pressure level in the ear canal up to a frequency-dependent saturation point, above which both D Stap and P SV showed a distinct deviation from proportionality with P EAC , suggesting that their relationship may remain constant at these high frequencies. Likewise, while the asymptotic value, and SPL at which saturation occurred were frequency dependent in both D Stap and P SV, the reduction in gain with increasing SPL above this level was constant above this level at all frequencies, and the magnitude of responses at harmonics of the driving frequency increased with increasing level, consistent with harmonic distortion via peak clipping. Importantly, this nonlinear distortion shifts the energy arriving at the inner ear to higher frequencies than are present in incident stimulus, thus exposing the high frequency sensitive components of the auditory system to more noise than would be expected from measurement of that stimulus on its own. Overall, responses suggest that the cochlear representation of very high-level air conducted stimuli is limited by nonlinearities in the middle ear, and that this peak limiting leads to increased high frequency cochlear exposures than are present in the driving stimulus.
Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest.
(Copyright © 2024 Elsevier B.V. All rights reserved.)
- Contributed Indexing:
Keywords: High-level sound; Intracochlear pressure; Laser doppler vibrometry; Peak clipping; Stapedial annular ligament; harmonic distortion
- Publication Date:
Date Created: 20240927 Date Completed: 20241103 Latest Revision: 20241103
- Publication Date:
20241104
- Accession Number:
10.1016/j.heares.2024.109121
- Accession Number:
39332208
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