To match or not to match: Caregiver Vocal Contingency, Affective Matching, and Infant Communication and Distress Signalling

Infants develop communicative display through proto-conversations with caregivers. Infant vocalisations elicit responses, shaping dyadic arousal. Infant and caregiver therefore grow together as a communicative and regulatory unit. In typical development autonomic arousal is initially closely linked to distress vocalisations, while communicative vocal display gradually becomes more independent of arousal over time. Individual differences in developmental trajectories suggest variation in these patterns.Using day-long home recordings from 5-18 month-old infants we examined how infant autonomic arousal relates to vocal behaviour and caregiver responsivity. We found a functional hierarchy in arousal–vocalisation coupling consistent with functional flexibility theory. Caregiver responsivity was arousal-contingent: higher rates of both 2-second and 5-second contingent responses during elevated arousal were associated with stronger coupling at medium–high arousal levels. Consistent with selective reinforcement theory, the more immediate window showed greater specificity and stronger effects than the proximal window.Within arousal levels, caregiver divergence in intensity and affect predicted fewer high-intensity and increased low-intensity vocalisations at moderate (but not elevated) arousal. Overall, findings suggest two interacting developmental mechanisms: broad caregiver responsivity supporting symbolic language via functional flexibility, and arousal-specific responsivity supporting a distress ‘alarm’ function. Variation in arousal-contingent caregiver responses may help characterise both typical and atypical developmental trajectories.