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.

Thanks to SPL Lab members

• Larry Humes (Investigator)

• Maureen Coughlin (Audiologist, ABD)

• Kelley Anderson (Research Assistant)

• Bill Mills (Programmer)

Formant Discrimination

• Just noticeable difference between standard vowel and one with shifted formant.

• Psychophysical procedures to determine thresholds formant frequency, F (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

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%)

Formant Thresholds Hi-Fi NH

0.0

25.0

50.0

75.0

100.0

125.0

150.0

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

ISO Hi-Fi

Word Hi-Fi

Sent Hi-Fi160%

190%

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

Hearing Impaired Listeners• 21 – 55 years old, N = 5

• Mild – moderate, high-frequency loss

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

• Audibility (70 vs 95) No

• Linguistic Context Yes (ISO, Word, Sent)

• Sent + ID task No

• Explain with figures

Summary Threshold ResultsFactor Significant

• Formant Frequency (8) Yes

1) Formant

Frequency

2)Audibility

Isolated Vowels Hi-fi

0.0

50.0

100.0

150.0

200.0

250.0

300.0

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

ISO NH 70

ISO HI 70

ISO HI 95

Sentences Hi-fi

0.0

50.0

100.0

150.0

200.0

250.0

300.0

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

Sent 95

Sent 70

3) Linguistic Context. Thresholds different

• Why?• Post-hocs, only F word < F Sent

Linguistic Context Hi-Fi HI

0

50

100

150

200

250

300

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

ISO

Word

Sent

Reversal, F Iso > F Word

Linguistic Context 95 dB Hi-Fi HI

0

50

100

150

200

250

300

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

ISO

Word

Comparison HI to NH (Hi-Fi)

HI vs. NH 70 dB SPL Hi-Fi

0

50

100

150

200

250

300

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

Word NH

Word HI

Sent NH

Sent HI

Thresholds Hi-Fi vs. Synthetic Speech

• Richie, Kewley-Port, & Coughlin (2003) reported F 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.

•Hi-Fi elevated by 150%

Hi-Fi vs. Syn Isolated Vowels Soft

0.0

50.0

100.0

150.0

200.0

250.0

300.0

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

Hi-Fi NH

Syn HI

Hi-Fi HI

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– hresholds for words better than isolated

vowels

Baseline Thresholds

• Normal Hearing Listeners (NH)

• Formant Synthesized (Syn)

• Female Isolated (ISO) Vowels F1 & F2

• Four Vowels: / I E Q Ã /Formant Thresholds Syn NH

0

10

20

30

40

50

60

70

80

90

100

ih1 eh1 uh1 ae1 uh2 ae2 eh2 ih2

Vowel formant

Delta F (Hz)

ISO

Linguistic Context Syn

Formant Thresholds Syn NH

0

10

20

30

40

50

60

70

80

90

100

ih1 eh1 uh1 ae1 uh2 ae2 eh2 ih2

Vowel formant

Delta F (Hz)

ISO 22 CVC

170%

Sent

250%

Added ID Task

Thresholds with or without ID Task Hi-Fi HI

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500

Formant frequency (Hz)

Threshold (Hz)

95 dB, Sen. 95 dB, sen+ID70 dB, sen70 dB, sen+ID

Audibility versus Pathology

• Vowels fully audible 70 dB NH, 95 dB HI

F2 elevated by 200 %Fully Audible HI vs. NH Word Hi-Fi

0

50

100

150

200

250

300

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel formant

Delta F (Hz)

NH 70

HI 95

Listener Variability at 70 dB for Word

0.0

100.0

200.0

300.0

400.0

ih1 eh1 uh1 ae1 uh2 eh2 ae2 ih2

Vowel Fromant

Delta F (Hz)

BAC

BCC

CLM

DLN

JRM