At birth, infants can respond to human voices. They are also capable of distinguishing among the voices of different people, and they begin to show a preference for the mother’s voice soon after birth. In one experiment, infants were given a pacifier that could record how often they sucked when they were awake. Then the researchers linked the infants’ sucking patterns to recordings of women’s voices so that when an infant increased or decreased the rate of sucking, it heard either its mother’s or another woman’s voice. Infants controlled their sucking to hear recordings of their mothers’ voices more often, showing that they preferred this voice to other voices.
DeCasper, A., & Fifer, W. (1980). Of human bonding: Newborns prefer their mothers’ voices. Science, 208, 1174