The biological stress response systems, including the Autonomic Nervous System (ANS), are thought to play a key role in co-regulation processes (Feldman, 2007a). Small but growing literature suggests that synchronous interactions may modulate mother-infant autonomic physiology such as cardiac activity (Feldman et al., 2011; Porter et al., 2022). Traditional gold standard physiological methods for the assessments of the ANS functioning include electrocardiography or skin conductance (Ioannou et al., 2014). These classical techniques require the use of contact sensors, restrictions of movements, and high levels of compliance of the participants, resulting in more invasive and less ecological ANS measurements. This can be of particular concern with very young populations where the compliance of participants cannot be assured, and all experimental manipulations might result in biased evaluation of infants' emotional state and of the dyadic interaction.
