The F0 fall delay of lexical pitch accent in Japanese Infant-directed speech

The current study examined the acoustic modifications of the lexical pitch accent in Tokyo Japanese infant-directed speech (IDS), with the focus on the F0 fall delay, where the alignment of the F0 turning points associated with pitch accents were delayed with respect to the accented mora. The RIKEN Mother- Infant Conversation Corpus (R-JMICC) [1] produced by 21 mothers from Tokyo area, was used to investigate the alignment of the F0 turning points. Two-piece linear regression was used to locate the turning points and the frequency of F0 fall delay was computed in IDS and in adult-directed speech (ADS). The results revealed that the frequency of F0 fall delay depended on the syllable structures of the accented syllable as well as the prosodic conditions (the presence of the boundary pitch movements and non-lexical lengthening) typically observed in Japanese IDS. We found significantly more frequent F0 fall delay in IDS compared to ADS, when the prosodic conditions were taken into account. The results indicate that the language specific prosodic structure should be considered in order to characterize the F0 fall delay of lexical pitch accents in IDS.