Developmental changes in voiced-segment ratio for Japanese infants and parents

Utterances of five Japanese infants and their parents were recorded longitudinally and used to develop an infant speech database. This database was used to analyze the voicedsegment ratio to investigate the developmental changes in utterances produced by infants and parents. The voicedsegment ratio is the ratio of the summed duration of a voiced segment to the total utterance duration. The analyses showed that the ratio tends to increase in an infant's utterances before the infant starts to produce 2-word sentences. The analyses also showed that, at the same stage, the ratio is higher in parents' infant-directed speech than in parents' adult-directed speech. These results suggest that the voiced-segment ratio reflects the development of an infant's utterance ability, and that a higher voiced-segment ratio is one of the characteristics of infant-directed speech.