Development of adaptive phonetic gestures in children: Evidence from vowel devoicing in two different dialects of Japanese

要旨

High vowels between voiceless consonants are often devoiced in many languages, as well as in many dialects of Japanese. This phenomenon can be hypothesized to be a consequence of the adaptive organization of the laryngeal gestures to various conditions, including dialectal requirements. If this theory is correct, it may be possible to predict developmental changes in vowel devoicing based on the developmental improvement in the dialect-specific organization of the laryngeal gestures. To test this expectation, the developmental properties of vowel devoicing were investigated for 72 children of 4 and 5 years of age, and 37 adults in two dialects of Japanese. One was the Osaka dialect, with a low devoicing rate, and the other the Tokyo dialect, with a high devoicing rate. In the Tokyo dialect, the devoicing rate of children significantly increased and reached an adultlike level by the age of 5 years, whereas it remained low irrespective of age in Osaka. The vowel devoicing of 5-year-old children exhibited the same characteristics as that of the adults of their respective dialect. These results suggest that children growing up with the Tokyo dialect acquire the articulatory gestures which do not inhibit vowel devoicing by the age of 5 years, whereas children growing up with the Osaka dialect acquire those which inhibit the devoicing of vowels by the same age. The results fit in well with the predictions of the gestural account of vowel devoicing. It is also suggested that learning dialect-specific adaptive strategies to coordinate voicing and devoicing gestures as required to attain an adultlike vowel devoicing pattern is a long process: By the age of 5 years children have completed enough of this process to become members of their dialectal community.

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