Modeling otoacoustic emission and hearing threshold fine structures

Area of Science:

• Auditory Neuroscience
• Acoustics
• Biophysics

Background:

• Human otoacoustic emissions and hearing thresholds exhibit complex frequency variations.
• Existing models struggle to fully capture these microstructural variations.
• Zweig and Shera proposed models based on wave reflections and cochlear activity patterns.

Purpose of the Study:

• To present a class of cochlear models that explain variations in human otoacoustic emissions and hearing threshold microstructure.
• To describe the quasiperiodic frequency variations (fine structures) observed in different types of otoacoustic emissions and hearing thresholds.
• To elucidate the relationships between these fine structures and the distortion product emission filter shape.

Main Methods:

• Developing cochlear models based on wave reflections from distributed spatial cochlear inhomogeneities.
• Incorporating tall and broad cochlear activity patterns as suggested by Zweig and Shera.
• Utilizing solutions of apical and basal moving cochlear wave equations in the absence of inhomogeneities for analysis.

Main Results:

• The models successfully describe quasiperiodic frequency variations in hearing thresholds, spontaneous, synchronous, click-evoked, and distortion-product otoacoustic emissions.
• The models accurately predict the relationships between these fine structures.
• A characteristic frequency spacing of approximately 0.4 bark, determined by the apical reflection function, is identified for most emissions and threshold microstructure.

Conclusions:

• The presented cochlear models provide a unified framework for understanding otoacoustic emissions and hearing threshold microstructure.
• The models highlight the crucial role of wave reflections and cochlear inhomogeneities in generating auditory fine structures.
• Predictions regarding frequency spacings for different emission types offer testable hypotheses for future research.