Do mothers enhance the tonal contrasts in their monosyllabic Cantonese tones directed to their infants?

Abstract

Introduction Some studies reported that adults enhanced acoustic differences of phonemes when speaking to young children. We examined whether mothers improved the contrasts among the lexical tones when speaking to infants. Methods Nineteen native Cantonese-speaking mothers produced the six Cantonese tones in 45 monosyllabic words to an adult and their 7- to 12-month-old infants. The 1709 words were low-pass filtered to preserve the pitch contours but eliminate lexical information. Five judges categorized the tones of the filtered words. Acoustic analysis was performed. Results Infant-directed tones had higher fundamental frequency (F0) and longer duration, but were identified with lower, though not significantly different, accuracy. Larger mean F0 differences were found in four pair of tones in infant-directed speech. However, these increased acoustic contrasts did not lead to higher perceptual accuracy of these tone pairs. Despite substantial perceptual confusion between T2 (HR) and T5 (LR) has been reported in previous tone studies, the difference in the slopes of the two tones was not enhanced in infant-directed speech. Conclusion Mothers acoustically modified their tones when speaking to infants. However, little evidence supported that mothers enhanced the phonetic contrasts of the tones in infant-directed speech. [Work supported by Research Grants Council of Hong Kong.]