Completing the loop with BabyX: harnessing a novel interactive experimental tool to uncover how infants' communicative signals shape caregivers' interactive responsiveness.

A limitation of social contingency research with infants is that scientists can only instruct the caregivers to modulate their interactive behaviour with the infant. This approach results in a one-sided perspective on social contingency where the infant is a passive recipient merely reacting to changing circumstances. Thus, with this approach it is not possible to investigate how infants actively shape social contingency. We propose the use of a novel realistic interactive digital model of a human child (named by its developers as 'BabyX') as an innovative social contingency research tool. This simulated digital child is autonomously animated by a cognitive architecture that can interact in real time with a social partner in human-like ways. Critically, researchers can manipulate the digital child's responsiveness to social contingency. In this article, we present three examples to illustrate the limits of current methodological approaches in social contingency research. Second, we introduce the digital child and highlight its usability to investigate social contingency. Third, we argue that studies with the digital child are key to closing the loop in social contingency research. It is our opinion that infants' communicative signals are key to shaping caregiver responsiveness. By employing BabyX we are in the unique position of being able to investigate not only how caregivers respond to infants' social contingency, but how infants actively shape social interactions. This article is part of the theme issue 'Mechanisms of learning from social interaction'.