Acoustic analysis of lexical tone in Mandarin infant-directed speech

Using Mandarin Chinese, a tone language in which the pitch contours of syllables differentiate words, the authors examined the acoustic modifications of infant-directed speech (IDS) at the syllable level to test 2 hypotheses: (a) the overall increase in pitch and intonation contour that occurs in IDS at the phrase level would not distort lexical pitch at the syllable level and (b) IDS provides exaggerates cues to lexical tones. Sixteen Mandarin-speaking mothers were recorded while addressing their infants and addressing an adult. The results indicate that IDS does not distort the acoustic cues that are essential to word meaning at the syllable level; evidence of exaggeration of the acoustic differences in IDS was observed, extending previous findings of phonetic exaggeration to the lexical level.