The acoustic basis of preferences for infant-directed singing

Acoustic differences between infant-directed and noninfant-directed singing were examined in 6 playsong and 4 lullaby pairs of recordings from Trainer (1996). Each mother had been recorded singing a song of her choice to her infant and singing the same song in the absence of her infant. For both playsongs and lullabies the tempo was slower, there was relatively more energy at lower frequencies, inter-phrase pauses were lengthened, and the pitch and jitter factor were higher in the infant-directed over infant-absent versions. Pitch variability was higher and the rhythm exaggerated (as measured by the relative duration of stressed to unstressed syllables) in the infant-directed versions of playsongs but not lullabies. Many of these acoustic modifications likely attract infants' attention, and playsongs and lullabies likely communicate different emotional messages.