Investigation of coarticulation in continuous speech of Japanese

This study analyzed coarticulation involved in continuous speech based on articulographic data obtained from three Japanese male speakers. Distribution of the articulation points of vowels and consonants revealed that speakers might compensate for morphological differences in the hard palate by adjusting the location of vowel articulation points. To evaluate the effects of the left and right phonemes on the target phoneme, three-phoneme sequences, consisting of five Japanese vowels (V) and ten apical and two palatal consonants (C), were extracted from read sentences and used in this analysis. A stepwise multiple regression method was used to analyze the phoneme sequences, in order to evaluate the ‘‘contributions’’ of the surrounding phonemes to the central one. The results showed that the horizontal component of the articulatory movement had a dominant function during articulation. The movement of the tongue tip was highly correlated to the tongue dorsum movement in the horizontal dimension, but was almost independent in the vertical dimension. This phenomenon suggested that coarticulation in VCV sequences can be considered as an independent consonantal gesture superimposed on a transitional portion between vowels. For apical-vowel combinations, the preceding consonant in CVC had a stronger effect on the vowel than the following one, but there was no dominance caused by the positions of the vowels in VCV sequences. For palatal-vowel combinations, the following phoneme showed a greater effect than the preceding phoneme in CVC sequences. In VCV sequences, the open and closed vowels showed different behaviors.