Multi-scale analysis of vocal coordination in infant-caregiver daily interaction

Infants participate in vocal coordination with others early in their life, even before they can rely on linguistic cues. They react sensitively to caregiver vocalizations, for instance, by imitating the caregiver and/or modulating their own vocalizations. When talking to an infant, caregivers also modulate their vocalizations, e.g., talk more slowly or with exaggerated prosody, which might attract infants’ attention and increase the clarity of vocal information. However, it is still unclear to what extent both parties’ vocal modifications dynamically influence each other. In this study, we investigate infants’ and caregivers’ vocal coordination in their daily interactions by applying multi-scale analysis on a global scale (i.e., a day), a middle scale (i.e., a conversational block), and a local scale (i.e., a turn). The day-long auditory recording data of nine infants, ages two months to three years, and their caregivers were analyzed. The results revealed that infants’ and caregivers’ vocalizations are differently coordinated on each timescale. On a global scale, infants and mothers react sensitively to each other’s vocalizations. Their conversation length varies across a day with a decreasing tendency. On a middle scale, infant-caregivers’ prosodic alignments increase over multiple turns in a conversation, indicating a continuous influence between them. Finally, more fine-grained analyses found that pitch-related features and pitch contours are aligned in each turn. The multi-scale analysis reveals the complexity of infant-caregiver interaction in the natural social environment, which inspires us to investigate the benefits of alignment in infants’ language learning at different timescales.