Developmental change of phoneme duration in a Japanese infant and mother

To investigate the early stage of speech development, the phoneme duration in an infant’s utterances and in a mother’s infant-directed speech (IDS) was analyzed for an infant between the ages of 4 and 45 months. In infant utterances, the durations of vowels and special moras gradually decrease as a function of month in entire period, whereas consonants such as fricatives, plosives, and semivowels rapidly decrease before the onset of two-word utterances. Almost all the phonemes in infant utterances except for plosives are longer than those in adult-directed speech (ADS) in entire period. In mothers’ IDS, vowels and long vowels gradually decrease in duration as a function of month, but most consonants do not. Phonemes in IDS except for fricatives and plosives are longer than those in ADS. These results indicate that, in terms of duration, developmental change is different for different phonemes in infant utterances and mothers’ IDS.