Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Speech, Language & Hearing Sciences

First Advisor

Kathryn H. Arehart

Second Advisor

James M. Kates

Third Advisor

Pui Fong Kan

Fourth Advisor

Phillip Gilley

Fifth Advisor

Rebecca Scarborough

Abstract

The purpose of this dissertation is to provide a baseline for developing the Speech Intelligibility Index (SII) for Korean. In the first study, the dynamic range (DR) of Korean speech was measured to analyze differences in DR across Korean, English, and Mandarin. Recorded sentence-level speech materials were used as stimuli. DR was quantified using different definitions of DR (defined as the range in dB from the highest to the lowest signal intensities), for several integration times (from 1 to 512 ms), and in different frequency bands (center frequencies (CFs) ranging from 150 to 8600 Hz). Across-language differences in DR were evident when considering frequency-band effects. Specifically, the DR for Korean was smaller than the English DR and the Mandarin DR in low-frequency bands (less than a CF of 455 Hz). Compared to Korean and Mandarin, the DR for English was smallest in mid-frequency bands (between a CF of 455 Hz and 4050 Hz) and was greatest in high-frequency bands (above a CF of 4050 Hz).

In the second study, band-importance functions (BIFs) for Korean were derived using procedures from Studebaker and Sherbecoe (1991) and Kates (2013). Seventy-eight native Koreans with normal hearing were tested with twenty-one low-pass (LP) and high-pass (HP) filtering conditions at varying signal-to-noise ratios (SNRs). Stimuli included 250 standardized Korean sentences presented in speech-shaped noise. BIFs produced by the two different procedures were similar. The BIF for Korean sentences showed that the frequency bands contributing most to speech intelligibility were near a CF of 350 Hz. The importance weights of the frequency bands below a CF of 630 Hz were 37.6% for the Studebaker and Sherbecoe (1991) procedure and 36.1% for the Kates (2013) procedure. Compared to published English and Cantonese BIFs for sentence and discourse materials, the present results showed that low-frequency regions (less than a CF of 840 Hz) were more important in the BIF for Korean sentences.

The accuracy of the SII for Korean may be improved by using the BIF and DRs for Korean speech. The results will provide insights into how to better optimize hearing-aid fittings for speakers of the Korean language.

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