Infants' prelinguistic vocalizations are rarely considered relevant for communicative development. As a result, there are few studies of mechanisms underlying developmental changes in prelinguistic vocal production. Here we report the first evidence that caregivers' speech to babbling infants provides crucial, real-time guidance to the development of prelinguistic vocalizations. Mothers of 9.5-month-old infants were instructed to provide models of vocal production timed to be either contingent or noncontingent on their infants' babbling. Infants given contingent feedback rapidly restructured their babbling, incorporating phonological patterns from caregivers' speech, but infants given noncontingent feedback did not. The new vocalizations of the infants in the contingent condition shared phonological form but not phonetic content with their mothers' speech. Thus, prelinguistic infants learned new vocal forms by discovering phonological patterns in their mothers' contingent speech and then generalizing from these patterns.

The early noncry vocalizations of infants are salient social signals. Caregivers spontaneously respond to 30-50% of these sounds, and their responsiveness to infants' prelinguistic noncry vocalizations facilitates the development of phonology and speech. Have infants learned that their vocalizations influence the behavior of social partners? If infants have learned the contingency between their vocalizing and the social responses of others, they should show an extinction burst when the contingency is removed, increasing their rate of noncry vocalizing then decreasing. Thirty-eight 5-month-olds were tested in the still-face paradigm, during which they engaged in a 2-min still-face interaction with an unfamiliar adult. When the adult assumed a still face, infants showed an extinction burst. This pattern of infant vocalizations suggests that 5-month-olds have learned the social efficacy of their vocalizations on caregivers' behavior. Furthermore, the magnitude of 5-month infants' extinction bursts predicted their language comprehension at 13 months.

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Two studies illustrate the functional significance of a new category of prelinguistic vocalizing-object-directed vocalizations (ODVs)-and show that these sounds are connected to learning about words and objects. Experiment 1 tested 12-month-old infants' perceptual learning of objects that elicited ODVs. Fourteen infants' vocalizations were recorded as they explored novel objects. Infants learned visual features of objects that elicited the most ODVs but not of objects that elicited the fewest vocalizations. Experiment 2 assessed the role of ODVs in learning word-object associations. Forty infants aged 11.5 months played with a novel object and received a label either contingently on an ODV or on a look alone. Only infants who received labels in response to an ODV learned the association. Taken together, the findings suggest that infants' ODVs signal a state of attention that facilitates learning.

Of major interest to those concerned with early mnemonic process and function is the question of whether early memories likely encoded without the benefit of language later are accessible to verbal report. In the context of a controlled laboratory study, we examined this question in children who were 16 and 20 months at the time of exposure to specific target events and who subsequently were tested for their memories of the events after a delay of either 6 or 12 months (at 22–32 months) and then again at 3 years. At the first delayed-recall test, children evidenced memory both nonverbally and verbally. Nonverbal mnemonic expression was related to age at the time of test; verbal mnemonic expression was related to verbal fluency at the time of test. At the second delayed-recall test, children evidenced continued accessibility of their early memories. Verbal mnemonic expression was related to previous mnemonic expression, both nonverbal and verbal, each of which contributed unique variance. The relevance of these findings on memory for controlled laboratory events for issues of memory for traumatic experiences is discussed.