Vowel length and stress in Thai

Abstract

It has been hypothesized that the relative importance of phonetic correlates of stress varies depending on the phonological structure of a language. If phonetic resources are used up in lexical phonology, it is predicted that they are unavailable or minimally available for signaling stress. Duration, one of the principal phonetic correlates of stress, is used to signal vowel length contrasts in Thai. The primary aim of this study was to examine the effects of stress on duration in signaling vowel length contrasts in Thai running speech. Stimuli consisted of 16 pairs of segmentally and tonally identical sentences representing four types of structural ambiguity and two types of stress patterns. In half of the pairs, keywords contained long vowels; in the other half short vowels. Syllable types of keywords were varied on the basis of the coda: nasal-ending vs. nonnasal-ending.Measures were taken of the duration of the vowel, nonvowel, and vowel + non-vowel intervals associated with keywords. All three intervals were significantly longer when stressed. Vowel durations were indistinguishable on the basis of vowel length category in unstressed syllables. Duration ratios of stressed to unstressed syllables remained constant between prosodic structures regardless of differences in either vowel length or syllable type. It is concluded that timing may be a dominant cue for stress across languages regardless of its uses for other phonological ends, and that timing, as in other languages, may be used to resolve structural ambiguities in Thai.