Project Summary The proposed study will investigate microstructure of early parent-infant play at behavioral and neural levels. The goal is to develop a novel method that combines a naturalistic head-mounted eye tracking system with EEG to pursues an innovative and significant idea in our field: that language learning emerges early at home and introduced socially (e.g., with the active participation of a parent), the early multisensory experience builds a perceptual and neural foundation that generates a positive cascading effect on subsequent language learning. The methodological aspect of the study aims to establish dynamic assessment approach–gaze coupled with neural activities—allows researchers to directly address the current limitation of studies using either head-mounted eye tracking system or EEG system alone. To the best of our knowledge, there is no previous work combining live naturalistic head-mounted eye tracking system and EEG, and this integrated task analysis will be performed in the context of social interaction with families of diverse backgrounds. Language learning occurs through social interaction and does so among widely diverse populations, and yet our understanding about how these processes are moderated across populations is limited. We propose a cross-sectional study (6- and 12-months- old) that entails observation of parent-infant object play while the infant wears a head-mounted eye tracker and EEG sensors in order to examine the potential neural significance (neural attentiveness measured by theta synchronization and alpha desynchronization) of coordinated visual experiences. The innovative project requires an interdisciplinary approach that combines expertise from our team members. The proposed research is a critical step toward advancing our understanding of early human multimodal perception and communication—a missing piece in theories of language development. The results ultimately will reveal a potential pathway in which social scaffolding shapes neural experiences and offers socially achievable prevention and amelioration of developmental deficits.