In chapter 3, we saw that the first step in vocal learning for preverbal infants is to acquire the ability to produce those qualities of cooing that are truly speech-like. This is accomplished through a give-and-take vocal exchange between the infant and the caregiver. Infant vocal production receives contingent stimulation from caregivers and is selectively reinforced. In terms of reinforcement, caregivers possess specific preferences for infant behaviour. Once infants come to utter truly speech-like cooing, this, in turn, affects the vocal behaviour of caregivers. Given caregiver preferences, in what ways do they tend to speak to infants? Then how do these specific utterances affect infants' vocal production?

Considerable scientific attention has been focused on the vocal quality of adults' early communication with their infants, for example, Ferguson's (1964) classic descriptions of the register of baby-talk. However, the functional significance of adult communication qualities for vocal development in very young infants is not yet fully understood. In this chapter, evidence will be presented suggesting the importance of one specific feature of the adult's response to early infant cooing – echoic responding – for the development of vocal imitation in the infant. Previously, the term echoic responding had been used to refer to a primitive form of infant imitation. However, when caregivers respond to infants in an echoic manner, infants listen to the ambient language and attempt to produce sound patterns that match what they hear.