Vowel variation in Japanese

A language’s use of the phonetic vowel space depends not only on how many vowel phonemes the language has, but on how each phoneme varies allophonically across contexts. This study tests the hypothesis that Japanese vowel allophones, measured from a wide range of contexts, will not fill the vowel formant space. This was predicted because Japanese has few vowel phonemes, distributed unevenly in the vowel space, and has no obvious processes of vowel reduction. Formant frequencies of vowel tokens from word lists and from read texts were compared for 7 speakers. These data show that, in Japanese, vowel allophones in prose fill in the vowel formant space more than allophones in word lists do, mainly as a result of centralization of the prose tokens. The use of the total formant space is determined in part by the distribution of phonemes, and in part by allophone centralization.