The acoustic characteristics of Japanese identical vowel sequences in connected speech

It has been pointed out that a word which contains an identical vowel sequence may not be distinguished, especially in faster speech, from a word which has a long vowel and phonologically the same mora-count. However, this indication has been made without any objective evidence and it is argued that a quantitative study is needed to investigate the acoustic characteristics of identical vowel sequence in comparison with those of a long vowel. This paper reports the results of production experiments for this purpose done by 10 native speakers of Japanese. The results will be discussed from the viewpoints of glottal stop insertion between an identical vowel sequence and durational ratio comparison. More specifically, the actual number of glottal stop insertions on citation and sentence levels will be clearly shown and the acoustic features of the glottal stop such as its duration will be investigated. In addition, the ratios of the whole token, consonant + vowel(s) and the vowel part of identical vowel sequence examples will be made clear and compared with those of long vowel examples in both citation and sentence reading forms.