Suppression of stimulus frequency otoacoustic emissions

Area of Science:

• Auditory Neuroscience
• Acoustics
• Human Physiology

Background:

• Otoacoustic emissions (OAEs) are sounds generated by the inner ear.
• Stimulus frequency evoked otoacoustic emissions (SFOAEs) are used to probe cochlear function.
• Understanding SFOAE generation and suppression is crucial for diagnosing hearing disorders.

Purpose of the Study:

• To investigate the suppression of SFOAEs by a secondary tone in human subjects.
• To analyze the frequency and level-dependent characteristics of SFOAE suppression.
• To model the nonlinear interactions within the cochlea responsible for SFOAE suppression.

Main Methods:

• SFOAEs were measured in human ears with a suppressor tone presented at various frequencies and levels relative to the stimulus tone.
• Data were collected across a range of stimulus tone levels (20-60 dB SPL) and frequencies.
• Results were fitted to a phenomenological model to quantify suppression characteristics.

Main Results:

• SFOAE suppression exhibited asymmetry, with higher-frequency suppressors being more effective at low levels, and lower-frequency suppressors at high levels.
• The observed asymmetry was modeled to estimate the nonlinear shape of the traveling wave envelope in the cochlea.
• The traveling wave envelope's peak sharpened at lower stimulus levels, indicating nonlinear behavior.

Conclusions:

• SFOAE suppression reveals nonlinear interactions within the cochlea.
• A quantitative model based on cochlear energy flow accurately predicts SFOAE suppression characteristics observed in human ears.
• These findings enhance our understanding of cochlear mechanics and provide a basis for improved diagnostic tools.