Compensating for ear-canal acoustics when measuring otoacoustic emissions

Area of Science:

• Auditory Neuroscience
• Acoustics
• Biomedical Engineering

Background:

• Otoacoustic emissions (OAEs) offer insights into cochlear function.
• Ear canal acoustics, including reflections and standing waves, compromise OAE measurement reproducibility.
• Existing methods like forward-pressure-level calibration do not fully resolve probe-location variability in distortion-product OAEs (DPOAEs).

Purpose of the Study:

• To develop a method for estimating the true outgoing OAE pressure wave at the eardrum.
• To separate emitted OAEs from ear canal reflections.
• To improve the diagnostic power of OAE measurements by reducing variability.

Main Methods:

• Measurement of conventional OAEs.
• Calculation of Emitted Pressure Level (EPL) to represent the OAE pressure wave in an idealized reflection-free ear canal.
• Comparison of DPOAE variability using conventional levels versus EPL.

Main Results:

• The Emitted Pressure Level (EPL) method successfully estimates the initial outgoing OAE pressure wave.
• Expressing DPOAEs using EPL significantly reduces their variation with probe location.
• Variability in EPL measurements approaches the test-retest repeatability of measurements at fixed probe positions.

Conclusions:

• EPL is a powerful tool for enhancing OAE measurement reliability.
• This method improves the sensitivity of OAEs for detecting cochlear changes.
• EPL offers a more accurate acoustic fingerprint of the inner ear.