Negative-delay sources in distortion product otoacoustic emissions

Area of Science:

• Acoustics
• Auditory Physiology
• Nonlinear Dynamics

Background:

• Distortion product otoacoustic emissions (DPOAEs) are crucial for assessing cochlear function.
• Time-frequency analysis of DPOAEs reveals complex delay components.
• Understanding these delays offers insights into cochlear mechanics and nonlinear processes.

Purpose of the Study:

• To investigate the origin of symmetrical positive and negative delay components in DPOAEs.
• To propose and test a model explaining the interplay between place-fixed and wave-fixed mechanisms.
• To explore the dynamic enhancement of these delay components.

Main Methods:

• Analysis of time-frequency representations of DPOAEs.
• Development of a theoretical model involving place-fixed modulation of wave-fixed nonlinear generators.
• Experimental validation using DPOAE measurements, including contralateral stimulation.
• Analytical solutions of a perturbed 1-d transmission line model.

Main Results:

• Observed symmetrical delay patterns in DPOAEs, including negative delays.
• Demonstrated that spectral amplitude and phase fluctuations are not always correlated.
• Proposed a model of place-fixed modulation of the nonlinear generator's spectral strength.
• Experimental data showed strong negative-delay sources, amplified by contralateral stimulation.

Conclusions:

• The symmetrical delay pattern in DPOAEs can be explained by place-fixed modulation of the nonlinear generator.
• Negative delays are significant and can be dynamically enhanced.
• The findings provide a deeper understanding of cochlear nonlinear acoustics and reflection mechanisms.