Sound spectrographic studies on the relation between motherese and pleasure vocalization in early infancy.

The relationship between the vocalizations of early infants and their mothers was investigated by acoustic analysis. The subjects were eight infants aged 40-70 days and their mothers. The infants were sufficiently developed to utter pleasure vocalization. The acoustic characteristics of the voices of the infants and mothers while communicating with each other analyzed in terms of pitch, duration, latency and melody types. The results were as follows: 1) Correlation was significant between the average fundamental frequencies of the infants' voices and those of their mothers. Motherese and infants' vocalizations were similar in pitch. 2) There was little individual difference in the duration of infants' vocalizations, but a considerable individual difference in the duration of motherese. No correlation was observed in the duration of the vocalizations of the infants and mothers. 3) The latencies of infant vocalization and motherese showed large differences among the infant-mother pairs. There was a tendency for the latency of the motherese to affect the number of utterances by the infant. 4) Significant correlations in the melody types were observed in three mother-infant pairs. These findings indicate that there are significant correlations in the vocal exchanges between infants and their mothers.