Differential effects of speaking rate and phonemic vowel length on formant frequencies of Japanese vowels

Abstract

This study examined the extent to which variation in speaking rate and phonemic vowel length affect the first two formant frequencies of Japanese vowels. If vowel duration is a factor that determines the degree of formant undershoot [Moon and Lindblom, J. Acout. Soc. Am. 96, 40–55 (1994)], formants of phonemic long vowels or vowels spoken at slower rates would occupy more peripheral areas in the F1/F2 vowel space than the short counterparts. Four male native speakers produced Japanese disyllabic non-words, /mVmV/, /mVVmV/, and /mVmVV/ (V=/i e a o u/, VV=/i: e: a: o: u:/) spoken in a carrier sentence at slow, normal, and fast rates. Effects of vowel length were clear for all five vowels: the long vowels occupied more peripheral areas of the vowel space than the short vowels. However, such a systematic effect was not found with speaking rate changes. ANOVAs performed on each vowel type indicated that, for non-high vowels /e(:) a(:) o(:)/, effects of vowel length and speaking rate interacted. The F2 of /e:/, for example, did not differ across rates, but the F2 of /e/ was significantly lower for faster rates. Implications are discussed in terms of Moon & Lindbloms formant undershoot model.