Temporal contingency of parent–infant vocal exchanges across dyadic and triadic interactive contexts

Early communicative exchanges are typically examined in dyadic contexts, yet infants develop within family systems that involve multiple caregivers. This study, involving 30 monolingual Italian mother-father-infant families, investigated how vocal contingency unfolds in dyadic and triadic interactions between mothers, fathers, and their 4-month-old infants. Thirty families were observed during structured face-to-face interactions including a mother-infant dyad, a father-infant dyad, and a triadic condition involving all three partners. Vocal data were coded frame-by-frame to compute bidirectional contingency measures between each partner pair. Linear mixed-effects models tested how vocal contingency varied across contexts. When contingency was calculated relative to infants' vocalisations (Partner-based contingency, PBC), both mothers and fathers showed lower response rates in triadic than dyadic interactions. In contrast, when calculated relative to each parent's own vocal activity (Self-based contingency SBC), contingency was higher in triadic settings, reflecting parents' reduced overall speech and a more selective alignment with infants' cues. Infants, in turn, showed higher contingency toward both parents in triadic interactions, suggesting heightened temporal organisation of infant vocal responses in multi-partner contexts. These findings suggest that, within the present structured laboratory context, temporal patterns of vocal contingency may differ between dyadic and triadic interactions, with infants and parents showing context-sensitive changes in the distribution of temporally contingent vocal exchanges. Triadic contexts may offer a useful setting for observing how infants and caregivers distribute vocal responsiveness across multiple partners.