Katherine Eulau ^1* Kathy Hirsh-Pasek ^1,2

• ¹ Temple University, Philadelphia, United States
• ² Brookings Institution, Washington D.C., District of Columbia, United States

Decades of research on joint attention, coordinated joint engagement, and social contingency link caregiver-child interaction in infancy as a foundation for language. These patterns of early behavioral synchrony contribute to the structure and connectivity of the brain in the temporoparietal regions typically associated with language skills. Thus, children attune to their communication partner and subsequently build cognitive skills directly relating to comprehension and production of language, literacy skills, and beyond. This has yielded marked interest in measuring this contingent, synchronous social behavior neurally. Neurological measures of early social interactions between caregiver and child, have become a hotbed for research. In this paper, we review that research and suggest that these early neural couplings between adults and children lay the foundation for a broader cognitive system that includes attention, problem solving, and executive function skills. This review describes the role of behavioral synchrony in language development, asks what the relationship is between neural synchrony and language growth, and how neural synchrony may play a role in the development of a broader cognitive system founded in a socially gated brain. We address the known neural correlates of these processes with an emphasis on work that examines the tight temporal contingency between communicative partners during these rich social interactions, with a focus on EEG and fNIRS and brief survey of MRI and MEG.Over the course of several decades, research established that a child's attention develops from visual attention, to shared attention, supported joint attention, coordinated joint attention, and symbol-infused coordinated joint attention (Bakeman et al., 1984;Adamson, et al., 2004). Coordinated joint attention, according to Bakeman, Adamson, and colleagues is a social interaction in which the child coordinates her attention with another person and the object with which that person is engaged (Bakeman et al., 1984). While joint attention is not an inherently linguistic activity, symbol-infused joint engagement is the expansion of coordinated joint attention into a communicative interaction with meaningful symbols (Adamson, et al., 2004). Numerous studies investigated the relation between early dyadic social interactions and language development (e.g.,