Marmoset Infant Vocal Development: Investigating Continuity and Parent-Mediated Vocal Learning

Abstract

Human vocal development is a dynamic, continuous process in which infants’ early pre-speech vocalizations serve as a template for later speech. It is also an interactive process whereby contingent parental vocal feedback shapes vocal learning. The extent to which non-human primates show continuity and learning in their vocal development is still unclear. This study attempts to shed light on these questions by examining the relationship between the cry and the adult-like phee to study continuity as well as the potential role of parents in the development of these calls to study vocal learning in the common marmoset (Callithrix jacchus). To support our hypothesis of a continuous relationship between the cry and phee, we first document the existence of the phee-cry. We also find that the syllable duration of the phee overlaps with that of the cry, suggesting that infants utilize the syllable duration of the cry as a model for phee development. This suggests that the phee emerges out of the cry. To investigate whether marmoset infants experience learning along with continuity, we examined the temporal dynamics of the transition from cry to phee production. We find that marmoset infants experience a sudden, rapid transition from largely producing cries to largely producing phees; this parallel transition in both call types indicates vocal learning with continuity in marmosets. Notably, this transition point varies between infants, raising the question of whether the degree of parental contingent responsiveness may explain the individual differences in the timing of the transition. We find that greater parental contingency to infant phees facilitates the transition to increased phee production. These findings present evidence that contrary to prior belief, non-human primates may be capable of vocal learning with continuity and that parents may mediate this process, similar to humans.