Children with severe disabilities have limited ability to communicate with their environment. Understanding how and to what extent these children connect with the environment can be an insurmountable challenge for their caregivers. In this thesis we investigated the degree of interactions between a pair of individuals using their physiological signals. It was hypothesized that stronger social interaction induces greater physiological synchrony. We introduced a multivariate index of synchrony to relate various physiological correlations into the degree of social interaction. 18 able-bodied individuals participated in a study to measure the extent of synchrony between two intimate individuals vs. two strangers during conversation. Stronger correlation was detected for intimate participants in comparison with the strangers. The physiological alignment also increased as the dyad interacted more. A generalization of our method can be used for the study of children with disabilities to understand the degree of their non-verbal interaction with their social environment.