Project Summary Caregiver-child dyadic interactions are central to early word learning and set the trajectory for later language development1,2. Past research typically focuses solely on parents’ role in determining the quality of early word learning experiences, leading to parent-focused interventions aimed at improving early language experiences3,4. However, these approaches often neglect that children are active, curious information-seekers who contribute substantially to structuring their own learning environment5,6. Understanding the behavioral and neural mechanisms of how children’s early learning curriculum is mutually negotiated in dyadic child-caregiver interactions may be key to predicting and reducing disparities in long-term language outcomes. The goal of the planned research is to understand how both caregiver scaffolding and children’s active information-seeking mutually contribute to effective word learning curricula. Central to this goal will be the evaluation of caregiver-child interactions in families spanning the full spectrum of socioeconomic status (SES). We will quantify variability in the dynamic negotiation of learning events between children and caregivers using multiple methods, including novel brain-to-behavior coupling methods and naturalistic observation, in order to trace early sources of individual differences in learning outcomes and word learning disparities. In Aim 1, we develop an experimental paradigm to test our hypothesis that word learning is most successful when caregivers and children jointly shape the learning input. In Aim 2, following technological advances in the Princeton Baby Lab, we investigate the neural mechanisms underlying successful dyadic structuring of the learning input by measuring dual-brain coupling between caregivers and children during word learning with functional near- infrared spectroscopy (fNIRS). In Aim 3, we quantify patterns of coordinated information structuring by children and caregivers during natural interactions in order to understand the ecological validity of the causal mechanisms tested in Aims 1 and 2. Together, this research will provide insight into behavioral and neural mechanisms that promote effective word learning curricula in dyadic child-caregiver learning events, with the ultimate goal of improving word learning and language development across the SES spectrum. Through these aims, the applicant will gain training in dual-brain neuroscientific techniques, broaden his theoretical training in language and cognitive development, and gain experience working with diverse populations and backgrounds, including across a wide SES spectrum. The sponsor, Dr. Casey Lew-Williams, has extensive experience providing mentorship in all of these training areas. The co-sponsor, Dr. Uri Hasson, is an expert in the study of neural coupling in dyadic interactions. The unique training environment at Princeton University provides the resources necessary to successfully complete the p...