Perceptual contribution of vowels to Mandarin sentence intelligibility under conditions of spectral degradation

Abstract

A recent study showed a vowel advantage over consonant to sentence intelligibility in Mandarin. Considering the fact that many important acoustic cues for sentence intelligibility are contained in the vowel segment, the present study investigated the effect of spectral degradation and its interaction effect with vowel duration on Mandarin vowel-only sentence intelligibility. Three types of spectrally degraded stimuli, including fundamental frequency flattened (F0F), sine-wave synthesized (SWS)and noise-vocoded(NV)vowel-only sentences, were generated. Different proportions of vowel centers were preserved by using a noise-replacement paradigm. Listening experiments showed that fundamental frequency contour only had a minimal effect to vowel-only sentence intelligibility, while harmonic cues had a more notable effect. Intelligibility of NV sentences was significantly lower than that of SWS sentences, suggesting other acoustic cues such as formant frequency information contribute to the vowel advantage when harmonic cues are discarded. Discarding vowel edges had a significantly negative effect on vowel-only sentence intelligibility under conditions of spectral degradation. The present study supports emphasis on the preservation of harmonic cues and vowel duration in speech processing strategies.