Individual differences in infants’ speech segmentation performance: The role of mother-infant cardiac synchrony

Introduction: Coregulation entails the regulatory processes that are embedded within infant-caregiver exchanges and it represents the first form of communication. While its presence may be evident at moments of infant distress, coregulation is also present during dyadic exchanges on a moment-to-moment basis. Recent studies have found a relation between behavioral and neural aspects of coregulation (emotional facial expressions, Vanoncini et al., 2022; social gaze and infant’s social brain, Vanoncini et al., 2024) and language learning. We investigated whether this link would extend to one of the first types of coregulation, namely biological coregulation, which was measured through recursive patterns of cardiac synchrony. We hypothesized that higher levels of cardiac synchrony are linked to better word segmentation. Methods: Twenty-eight 9-month-old infants (16 females) and their German-speaking mothers participated in the study. We asked mothers to play for 5 minutes with their infant as they would do at home. During this time, through dual-electrocardiogram, we measured Respiratory Sinus Arrhythmia, a biomarker commonly used for parent-child cardiac synchrony. Then, we examined infants’ word-segmentation ability with a central fixation paradigm using eye-tracking. Stimuli were based on Bartels and colleagues (2009). We familiarized infants with auditory text passages in German and measured looking times while listening to familiar versus novel test words. Following cross-recurrence quantification analysis, we used entropy (ENTR; degree of predictability characterizing the dyadic system) and cross recurrence rate (cross RR; tendency of the dyadic system to repeat itself) as measures of cardiac synchrony. Results: Regression modelling revealed that cross RR, but not ENTR, interacted with trial type: the higher the cross RR of mother’s and infant’s RSA during interaction, the longer infants looked during presentation of novel compared to familiar words at test, indicating an advanced word segmentation. Thus, individual differences in infants’ word segmentation relate to the tendency of the dyadic system to repeat itself, rather than its predictability, of cardiac synchrony during mother-infant interactions. Conclusion: Our study highlights how synchronized social interactions, starting from their physiological level, might have a positive impact on communication effectiveness and the creation of an interconnected environment for language growth.