Spontaneous basilar-membrane oscillation (SBMO) and coherent reflection.

Area of Science:

• Auditory neuroscience
• Bioacoustics
• Mathematical modeling

Background:

• Spontaneous oscillations of the basilar membrane (SBMO) at 15 kHz, accompanied by spontaneous otoacoustic emissions (SOAEs), were previously observed.
• The mechanical frequency response of the basilar membrane exhibits spectral peaks not explained by single-site reflection models.

Purpose of the Study:

• To investigate the phenomenon of 'coherent reflection' as a potential explanation for spectral peaks in basilar membrane response.
• To model the cochlea and artificially evoke coherent reflection to understand its effect on mechanical frequency response.

Main Methods:

• A three-dimensional computational model of the cochlea was developed.
• Random place-fixed irregularities were introduced to the basilar membrane impedance to evoke coherent reflection.
• The frequency spectrum of the basilar membrane response to random noise stimulus was analyzed.

Main Results:

• The model demonstrated a series of spectral peaks in the basilar membrane response, mimicking experimental findings.
• These peaks result from the superposition of the primary wave and a coherent reflection wave originating from the stapes.
• The relative peak sizes diminished with increased stimulus intensity, consistent with experimental data.

Conclusions:

• Coherent reflection is identified as the likely cause of the observed spectral peaks in the basilar membrane response.
• The concept of coherent reflection also explains the level-dependent nature of these peaks.
• A minor refinement of the conditions required for coherent reflection to occur was proposed.