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Multiple internal reflections in the cochlea and their effect on DPOAE fine structure
Sumitrajit Dhar1, Carrick L Talmadge, Glenis R Long
1Department of Speech and Hearing Sciences, Indiana University, Bloomington, Indiana 47405, USA. sumit@indiana.edu
The Journal of the Acoustical Society of America
|January 2, 2003
Summary
Distortion product otoacoustic emissions (DPOAEs) fine structure is influenced by two cochlear sources and multiple internal reflections. These reflections create previously unreported DPOAE patterns, especially at higher stimulus ratios, impacting interpretation.
Area of Science:
- Auditory neuroscience
- Otoacoustic emissions research
- Hearing science
Background:
- Distortion product otoacoustic emissions (DPOAEs) are crucial for assessing cochlear function.
- Current models often consider two primary cochlear sources for DPOAE generation.
- The fine structure of DPOAEs, characterized by frequency-dependent variations, is complex and not fully explained by simple models.
Purpose of the Study:
- To investigate the influence of multiple internal reflections on DPOAE fine structure.
- To identify and characterize novel patterns in DPOAE amplitude and group delay.
- To determine the conditions under which multiple internal reflections significantly affect DPOAEs.
Main Methods:
- DPOAEs were recorded from four subjects across a range of f2/f1 ratios (1.053 to 1.36) with precise frequency increments.
- DPOAE amplitude and group delay were analyzed for fine structure variations.
- An inverse Fast Fourier Transform (FFT) algorithm was employed to analyze DPOAE data in the time domain.
Main Results:
- Previously unreported DPOAE patterns, termed "exotic" patterns, were observed in addition to the standard log sine variation.
- These exotic patterns correlate with the presence of multiple internal reflections within the cochlea.
- Multiple internal reflections were more frequently observed at high primary frequency ratios (f2/f1 ≥ 1.3).
Conclusions:
- A comprehensive understanding of DPOAEs requires consideration of both two-generation sources and multiple internal reflections.
- Multiple internal reflections contribute significantly to the observed DPOAE fine structure, particularly under specific stimulus conditions.
- The findings necessitate refinement of DPOAE interpretation models to incorporate the effects of internal reflections for accurate cochlear assessment.