The Acoustic Characteristics of Infant-Directed versus Adult-Directed Speech and Song

Abstract

Infant-directed (ID) speech is characterized by increased pitch, greater pitch variability, slower rate, and greater vowel space compared to adult-directed (AD) speech. Less is known about ID song, but research suggests that it exhibits increased mean pitch and longer vowel durations when compared to ID speech. The present study investigates the acoustic characteristics of the corner vowels (/i/, /u/, and /ɑ/) in ID and AD song and speech. ID vocalizations were characterized by significantly higher fundamental frequency (f0), duration, vowel space, global vowel dispersion, and within-category vowel dispersion compared to AD vocalizations. Similarly, song was associated with significantly higher measures of f0 and length than speech but was uniquely characterized by reduced f0 variability and increased duration variability when compared to speech. The increase in f0 and f0 variability associated with infant-directedness was much smaller in song than in speech, suggesting that acoustic modifications associated with ID vocalizations are constrained in song.