Japanese sokuon, or geminate consonant, is claimed to affect the duration of the adjacent vowels on both sides. Previous studies have found that vowels are longer before sokuon and they are shorter after sokuon. The speech materials used in these studies are read-aloud phrases or short sentences. In order to evaluate if these findings hold true in spontaneous speech, we analyzed the Corpus of Spontaneous Japanese. The results revealed that vowels as well as mora nasals are longer before sokuon. However, no clear tendencies appeared for the duration of vowels after sokuon. The effect of sokuon on the preceding vowel is robust in both stop consonants and in fricatives. Articulatory correlations with the vowel duration are discussed.
