Local cochlear damage reduces local nonlinearity and decreases generator-type cochlear emissions while increasing...

Area of Science:

• Auditory Neuroscience
• Otoacoustic Emissions Research
• Cochlear Mechanics

Background:

• Distortion product otoacoustic emissions (DPOAEs) are generated by cochlear nonlinearity.
• DPOAEs measured in the ear canal are a sum of different emission types.
• Understanding the intracochlear sources of DPOAEs is crucial for auditory research.

Purpose of the Study:

• To investigate the intracochlear origins of DPOAEs.
• To examine the impact of localized cochlear nonlinearity reduction on DPOAEs.
• To differentiate between generator and reflector components of DPOAEs.

Main Methods:

• Simultaneous ear canal and intracochlear pressure measurements in gerbils.
• Creation of a localized cochlear damage model.
• Evoking DPOAEs using varying frequency ratios (f(2)/f(1)) in healthy and damaged cochleae.

Main Results:

• Reduced DPOAEs were observed in damaged cochlear regions for wide f(2)/f(1) stimuli, correlating with decreased nonlinearity.
• DPOAEs evoked by narrow f(2)/f(1) stimuli showed complex bimodal changes (decrease and increase) in adjacent frequency bands.
• Steepened DPOAE phase-vs-frequency slopes were noted in damaged cochleae.

Conclusions:

• Local cochlear nonlinearity significantly influences DPOAE generation.
• The findings support the complex, multi-component nature of DPOAEs.
• Intracochlear measurements are vital for dissecting DPOAE generation mechanisms.