Vowel formant discrimination in high-fidelity speech by hearing-impaired listeners.

1. Vowel formant discrimination in high-fidelity speech by hearing-impaired listeners. Diane Kewley-Port, Chang Liu (also University at Buffalo,) T. Zachary Burkle Indiana University, SPHS Presented at the Acoustical Society of America Meeting, Austin, TX, Nov. 11, 2003.

2. Thanks to SPL Lab members • Larry Humes (Investigator) • Maureen Coughlin (Audiologist, ABD) • Kelley Anderson (Research Assistant) • Bill Mills (Programmer)

3. Formant Discrimination • Just noticeable difference between standard vowel and one with shifted formant. • Psychophysical procedures to determine thresholds formant frequency, DF (Hz). • For 10+ years, experiments have systematically varied conditions, phonetic context, F0, noise etc. • Purpose: Examine formant thresholds for hearing-impaired listeners (HI) in nearly natural speech, including sentences

4. High-Fidelity Speech • To preserve naturalness, use STRAIGHT (Kawahara et al., 1999) synthesis • Stimulus Samples for word “bad” • Sentence • Word (standard vowel) • Word (10% F1 increment, NH, optimal listening Weber Fraction = 1.5%)

6. Experimental Factors for HI study • Formant Frequency: / I E Q Ã / F1 & F2 • Audibility: 70 dB SPL partial vs. 95 dB SPL fully • Linguistic Context: isolated vowels, words, sentences • Sent + ID task: Sentence discrimination only vs. Sentence discrimination + ID

7. Hearing Impaired Listeners • 21 – 55 years old, N = 5 • Mild – moderate, high-frequency loss

8. Procedures • Day 1 Screening • Days 2-4 Training • Days 5-23 Testing • Linguistic Context (ISO, Word, Sent) and Sent + ID blocks randomized daily • 95 vs. 70 dB SPL levels fixed each day

9. Summary Threshold ResultsFactor Significant • Formant Frequency (8) Yes • Audibility (70 vs 95) No • Linguistic Context Yes (ISO, Word, Sent) • Sent + ID task No • Explain with figures

10. 1) Formant Frequency 2)Audibility

12. Post-hocs, only DF word < DF Sent 3) Linguistic Context. Thresholds different • Why?

13. Reversal, DF Iso > DF Word

14. Comparison HI to NH (Hi-Fi)

15. Thresholds Hi-Fi vs. Synthetic Speech • Richie, Kewley-Port, & Coughlin (2003) reported DF for isolated formant synthesized vowels (Syn) for HI • Liu & Kewley-Port (2003) report for NH no difference Hi-Fi and Syn for isolated vowels and words • Predict that thresholds for our Hi-Fi • vowels same as Syn vowels from Richie et al.

16. Hi-Fi elevated by 150%

17. Summary • Formant discrimination by HI significantly effected by • Formant Frequency • Linguistic Context • Speech quality (Hi-Fi harder) • Surprising Hi-Fi threshold comparisons • Thresholds for softer sentences better than louder • Thresholds for words better than isolated vowels

18. Baseline Thresholds • Normal Hearing Listeners (NH) • Formant Synthesized (Syn) • Female Isolated (ISO) Vowels F1 & F2 • Four Vowels: / I E Q Ã /

19. Linguistic Context Syn

20. Added ID Task

21. Audibility versus Pathology • Vowels fully audible 70 dB NH, 95 dB HI DF2 elevated by 200 %