This project will examine the timing of vocalizations in interactions between infant siblings of children with ASD and their caregivers throughout the first year of life in order to look for early warning signs of ASD and inform early interventions. From the first days of life, infant and caregiver interactions involve mutual give-and-take that is very important for infant development. One example of this is the way in which typically developing infants and their mothers adjust the timing of their vocalizations to coordinate with one another, much like two adults having a conversation. Coordination of the timing of vocal behavior with a partner involves a mix of attention, language development, and social engagement--and for that reason, it may be an ideal context in which to look for early symptoms of autism spectrum disorder. In addition, while a lot of research on ASD has focused on individual characteristics of the child, this study will help us understand infant behavior in the context of everyday social interaction, and will therefore have implications for early interventions focused on parent-child interaction.