Birdsong is considered a model of human speech development at behavioral and neural levels. Few direct tests of the proposed analogs exist, however. Here we test a mechanism of phonological development in human infants that is based on social shaping, a selective learning process first documented in songbirds. By manipulating mothers' reactions to their 8-month-old infants' vocalizations, we demonstrate that phonological features of babbling are sensitive to nonimitative social stimulation. Contingent, but not noncontingent, maternal behavior facilitates more complex and mature vocal behavior. Changes in vocalizations persist after the manipulation. The data show that human infants use social feedback, facilitating immediate transitions in vocal behavior. Social interaction creates rapid shifts to developmentally more advanced sounds. These transitions mirror the normal development of speech, supporting the predictions of the avian social shaping model. These data provide strong support for a parallel in function between vocal precursors of songbirds and infants. Because imitation is usually considered the mechanism for vocal learning in both taxa, the findings introduce social shaping as a general process underlying the development of speech and song.

Few studies have focused on mechanisms of developmental change during the prelinguistic period. The lack of focus on early vocal development is surprising given that maternal responsiveness to infants during the first two years has been found to influence later language development. In addition, in a variety of species, social feedback is essential for vocal development. Previous research demonstrated that maternal feedback to prelinguistic vocalizations influenced the production of more developmentally advanced vocalizations, suggesting that effects of maternal responsiveness on vocal development may start during the prelinguistic phase; however, because mothers were instructed how and when to respond to their infants' vocalizations, the timing and type of typical maternal feedback is unknown. In the present study, we analyzed unstructured play sessions for 10 mother-infant dyads to explore the relationship between prelinguistic vocal production and maternal responsiveness. Mothers responded contingently to prelinguistic vocalizations over 70% of the time. Mothers responded with more vocal responses compared to interactive responses (e.g., gazes, smiling, physical contact). Investigation of specific types of vocal responses revealed that mothers responded mainly with acknowledgments to both vowel-like sounds and consonant-vowel clusters. Mothers also showed differential responding to vocalizations that varied in quality. Mothers responded with play vocalizations to vowel-like vocalizations significantly more than to consonant-vowel clusters, whereas they responded with imitations to consonant-vowel clusters more than to vowel-like sounds. Mothers, therefore, appeared to regulate their contingent feedback relative to the speech-like quality of infants' vocalizations which may provide relevant stimulation to guide communicative development.

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.

All organisms inherit parents' genes, but many also inherit parents, peers, and the places they inhabit as well. We suggest the term ontogenetic niche to signify the ecological and social legacies that accompany genes. A formal name is needed to give the idea of the inherited environment equal status with its conceptual cognates; nature and nurture. We argue here that increased recognition of the inherited environment facilitates unification efforts within the developmental sciences by emphasizing the affinity, rather than opposability, of ontogenetic processes.

For effective communication, infants must develop the phonology of sounds and the ability to use vocalizations in social interactions. Few studies have examined the development of the pragmatic use of prelinguistic vocalizations, possibly because gestures are considered hallmarks of early pragmatic skill. The current study investigated infant vocal production and maternal responsiveness to examine the relationship between infant and maternal behavior in the development of infants' vocal communication. Specifically, we asked whether maternal responses to vocalizations could influence the development of prelinguistic vocal usage, as has been documented in recent experimental studies exploring the relation between maternal responses and phonological development. Twelve mother–infant dyads participated over a six‐month period (between 8 and 14 months of age). Mothers completed the MacArthur Communicative Development Inventory when infants were 15 months old. Maternal sensitive responses to infant vocalizations in the previous months predicted infants' mother‐directed vocalizations in the following months, rather than overall response rate. Furthermore, mothers' sensitive responding to mother‐directed vocalizations was correlated with an increase in developmentally advanced, consonant–vowel vocalizations and some language measures. This is the first study to document a social shaping mechanism influencing developmental change in pragmatic usage of vocalizations in addition to identifying the specific behaviors underlying development.

Female cowbirds raised in auditory isolated from males responded to the songs of male cowbirds with copulatory postures. The songs of males reared in isolated were more effective in eliciting the posture than the songs of normally reared males. The females did not respond to the songs of other species. These results indicate one mechanism of species identification for this parasitic species.

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