Acoustic determinants eliciting Japanese infants' vocal response to maternal speech.

Generally, infants prefer infant-directed speech to adult-directed speech. This study investigated which acoustic features of maternal infant-directed speech elicit effectively 3-mo.-old infants' vocal response. The participants were 40 Japanese mother and infant dyads. Vocal f0 from the mother's speech and the infant's vocalization was extracted using Computerized Speech Laboratory (CSL4300) and custom software. The acoustical features measured were mean fundamental frequency (f0), and f0 contour. The rate of the infant's vocal response was significantly higher When the maternal infant-directed speech was terminated with a falling contour rather than a rising or flat contour. There was no significant difference between the mean f0 of the maternal infant-directed speech followed or not followed by the infant's vocal response. This suggests that the falling contour of terminal maternal infant-directed speech serves to elicit the 3-mo.-old infant's vocal response.