Mothers do not enhance phonemic contrasts of Mandarin lexical tones in child-directed speech

Abstract

Child-directed speech is characterized by higher pitch, more expanded pitch contours, and more exaggerated phonetic contrasts, which was suggested to facilitate speech sound acquisition. This study examined the perceptual and acoustic differences of mothers' disyllabic Mandarin lexical tones directed to adults and children to determine whether mothers exaggerated the pitch targets of the four Mandarin tones when speaking to children. Twelve Mandarin-speaking mothers produced 700 child-directed (CD) and adult-directed (AD) disyllabic words in a picture naming task. Five Mandarin-native speakers identified the mothers' AD and CD tones in filtered speech. Overall, CD lexical tones were identified with significantly lower accuracy than AD lexical tones (89% vs. 94%, S = 25.5, p = 0.006, r = 0.927, Wilcoxon Signed Rank Test). Acoustic analysis showed that the mean fundamental frequency (f0) of the four tones in both syllables was significantly higher in CD than in AD productions. No difference was found between AD and CD in the distinctive pitch targets for the 4 tones, namely pitch shift for Tone1, F0 slope for Tone2, minimum F0 for Tone3 and F0 slope for Tone4. F0 plots showed mostly parallel contours in AD and CD productions without exaggeration of the phonetic contrasts of the tones. [Work supported by NIDCD F31 DC008470-01A1.]