This project will expand an ongoing study led by Dr John Constantino, which is developing two ways to quantify social behavior in young children. Currently, typically developing children, children with autism and children at risk for autism are included. However, funding for this project will allow the researchers to collect data on individuals with Williams Syndrome (WS). In contrast to people with ASD, people with WS are intensely social, even from an early age. Interestingly, while their behaviors are different, they share certain genetic markers with some people with autism. Therefore, including this comparison group will not only improve the accuracy of the instruments, but also better characterize the contribution of these genes to social behavior.