Processing of Japanese vowel devoicing and the effect of speech rate

Abstract

Vowel devoicing (or reduction) in Japanese is an interface between the phonetic and phonological levels (Vance, 1987; Yoshida, 2002). The phonological rule for vowel reduction defines that high vowels (/i, u/) undergo reduction when between voiceless consonants or between a voiceless consonant and a pause. However, there are some cases of vowel reduction that do not fit the rule. A high vowel adjacent to a voiced consonant sometimes becomes reduced, especially in casual speech (Arai, 1999). Even a nonhigh vowel can undergo reduction (Arai, 1999; Vance, 2004). In this study, the effect of speech rate on the processing of reduced vowels is examined, particularly for vowels that are only likely to be reduced in casual, fast speech. How do listeners recognize vowels that are reduced in fast speech, or the words containing them? A lexical decision experiment showed that listeners found it easier to process fast speech containing reduced vowels than careful speech of isolated words containing them. They also found vowel reduction acceptable for nonhigh vowels in fast speech. This suggests that listeners use knowledge of both phonology and speech rate variability in processing connected speech.