Evoked otoacoustic emissions as cochlear Bragg reflections.

Area of Science:

• Auditory Neuroscience
• Acoustics
• Biophysics

Background:

• Evoked otoacoustic emissions (EOAEs) are crucial for hearing diagnostics.
• The origin of long group delays in EOAEs remains incompletely understood.
• Basilar membrane (BM) mechanics play a key role in cochlear wave propagation.

Purpose of the Study:

• To mathematically model cochlear wave reflection mechanisms.
• To identify the source of long group delays in EOAEs.
• To explain various characteristics of EOAEs, such as their spectral structure and dependence on sound pressure level (SPL).

Main Methods:

• Mathematical modeling of cochlear wave reflection.
• Analysis of 'wave-related' and 'BM-related' scattering mechanisms.
• Investigation of Bragg reflection at periodic BM inhomogeneities.

Main Results:

• 'Wave-related' reflections do not explain long group delays.
• 'BM-related' scattering due to inhomogeneities is a plausible explanation.
• Bragg reflection at periodic BM variations accounts for observed long delays, frequency dependence, and echo structures.

Conclusions:

• Basilar membrane inhomogeneities, specifically periodic variations, are likely responsible for Bragg reflection generating EOAEs.
• This model explains the frequency-dependent long group delays and complex echo structures observed in EOAEs.
• The findings suggest that middle/inner ear mismatch is not necessary to explain these phenomena.