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A Taxonomy-Based Approach of Inferring Cochlear Compression from Otoacoustic Emissions
Abstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology (2017)
  • Anusha Yellamsetty, University of Memphis
  • Shaum P. Bhagat, University of Memphis
Listeners with normal hearing are capable of detecting minute increments of sound pressure across a wide dynamic range (WDR) of sound levels. A critical process that accommodates listener sensitivity across this WDR is the compression initiated on the basilar membrane (BM). Otoacoustic emission (OAE) input/output (I/O) measures are one of the indirect methods to infer characteristics of cochlear compression in humans. According to current theory, distortion-product OAEs (DPOAE) are classified as primarily distortion source OAEs and stimulus-frequency otoacoustic emissions (SFOAE) are classified as primarily reflection source OAEs. In order to evaluate source contributions to cochlear nonlinearity, compression characteristics were inferred from both DPOAE I/O functions and SFOAE I/O functions in normal-hearing listeners at low and high test frequencies.

Two models that have been proposed for inferring OAE I/O function compression were utilized. These models consisted of a third-order polynomial regression model and a three-segment linear regression model. Measurements of DPOAE I/O and SFOAE I/O functions were obtained in two groups of normal-hearing listeners. The first group was tested at 750 Hz and 2 kHz, and the second group was tested at 3 kHz, 4 kHz, and 6 kHz. The DPOAE and SFOAE I/O functions were fitted with the two models to derive compression thresholds (CT) and compression slopes (CS). 

The results indicated little redundancy between the third-order polynomial model and the three-segment model. There were no statistically significant correlations between DPOAE CT and SFOAE CT at any test frequency within both models. Trends in the data indicated that high test frequencies had lower CT than lower test frequencies. Estimated compression values obtained from CS were higher at higher test frequencies compared with lower test frequencies.

Since there is little redundancy between the models, comparing results across models is not an ideal way to draw conclusions concerning BM compression. The independence of DPOAE and SFOAE CT is indicative of different source origins. Differences in observed inferred compression characteristics, with lower CT and higher values of compression at high test frequencies compared to low test frequencies, is consistent with physiological studies of BM compression in animal models. Efforts at comparing cochlear compression inferred from an OAE taxonomy-based approach with compression inferred from behavioral masking functions will lead to a greater understanding of the cochlear compression mechanisms that accommodate WDR in normal-hearing listeners. Acknowledgements: The authors wish to thank Dr. Enrique Lopez-Poveda for his assistance with the three-segment model.
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Citation Information
Anusha Yellamsetty and Shaum P. Bhagat. "A Taxonomy-Based Approach of Inferring Cochlear Compression from Otoacoustic Emissions" Abstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology Vol. 40 (2017) p. 53 - 54
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