Speech rate and pitch characteristics of infant-directed speech: Longitudinal and cross-linguistic observations.

The speech rate and pitch (F0) characteristics of naturalistic, longitudinally recorded infant- and adult-directed speech are reported for three, genetically diverse languages. Previous research has suggested that the prosodic characteristics of infant-directed speech are slowed speech rate, raised mean pitch, and expanded pitch range relative to adult-directed speech. Sixteen mothers (5 Sri Lankan Tamil, 5 Tagalog, 6 Korean) were recorded in their homes during natural interactions with their young infants, and adults, over the course of 12 months beginning when the infant was 4 months old. Regression models indicated that the difference between infant- and adult-directed speech rates decreased across the first year of infants' development. Models of pitch revealed predicted differences between infant- and adult-directed speech but did not provide evidence for cross-linguistic or longitudinal effects within the time period investigated for the three languages. The universality of slowed speech rate, raised pitch, and expanded pitch range is discussed in light of individuals' highly variable implementation of these prosodic features in infant-directed speech.