Contrast enhancement and the distribution of vowel duration in Japanese

• The position of vowels in linguistic units (intonation phrase and word) and the length of the units affect vowel duration. • Patterns of vowel duration are different depending on the scale (intonation phrase/word). • At the word level only, the vowel length contrast is enhanced in earlier positions or shorter words, and reduced in others. • Variations in vowel duration balance the transmission of lexical information and the cost of phonetic implementation. This paper offers a case study of the role of information in patterns of segmental duration, focusing on the short vs. long vowel contrast in Japanese. We confirmed that the position of vowels in linguistic units (intonation phrase/IP and word) and the length of the units affect vowel duration, but the patterns differ depending on the type of units. The results suggest that at the word level, vowel duration patterns in such a way that cues for vowel contrast are enhanced in salient (earlier) positions and units with less predictability or more lexical competitors (shorter words), while cues are relatively reduced in non-salient (later) positions and units with more predictability or less lexical competitors (longer words). In this way, the variation in vowel duration balances the successful transmission of lexical information and the cost for phonetic implementation, which supports previous findings in communication-based approaches of language.