Kaiki and Sagisaka (1992) showed that part of speech has small effect on the duration, i.e., independent (content) words are generally longer than dependent (function) words in vowel duration[39]. We used the word database that consisted of content words. Related to accent, which is usually considered as an important factor in stress-timed languages such as English, many researchers showed that pitch accent has no significant influence on vowel duration in Japanese[37][38].
