Duration and F0 cues for vowel length in Japanese

Two acoustic cues for the long–short vowel contrast were investigated in productions of Japanese accented vowels under two rates of speech. An accented word has a high–low pitch sequence. Long accented vowels have the fall within the syllable, while short vowels do not. Unsurprisingly, the vowel duration was significantly shorter in fast speech than in slow speech overall. The speech rate affected the long vowel duration more than the short vowel duration; the ratio between short vowels and long vowels varied by speech rate: 1:1.7 in fast speech and 1:1.9 in slow speech. However, the pitch fall was not significantly affected by the speech rate in either type of vowel. These results suggest that for native Japanese speakers, pitch information may be a more stable cue than duration for distinguishing the length of accented vowels. A perception study manipulating these cues is in progress. Synthesized long vowels without the pitch fall characteristic of long accented vowels are compared with normally accented long and short vowels. If Japanese speakers perceive the synthesized vowels as short, this constitutes evidence that for accented vowels, the pitch cue dominates the duration cue.