Development of allophonic realization until adolescence: A production study of the affricate-fricative variation of /z/ among Japanese children
The development of allophonic variants of phonemes is poorly understood. Thus, this study aimed to examine when children typically begin to articulate a phoneme with the same allophonic variant typically used by adults. Japanese children aged 5-13 years and adults aged 18-24 years participated in an elicited production task. We analyzed developmental changes in allophonic variation of the phoneme/z/, which is realized variably either as an affricate or a fricative. The results revealed that children aged nine years or younger realized/z/as affricate significantly more than 13-year-old and adult speakers. Once the children reached 11 years of age, the difference compared to adults was not statistically significant, which denotes a similar developmental pattern as that of speech motor control (e.g., lip and jaw) and cognitive-linguistic skill. Moreover, we examined whether the developmental changes of allophonic realization of/z/are due to speech rate and the time to articulate/z/. The results showed that the allophonic realization of/z/is not affected by these factors, which is not the case in adults. We also found that the effects of speech rate and the time to articulate/z/on the allophonic realization become adult-like at around 11 years of age.