Because autism spectrum disorders (ASD) is not diagnosed reliably before the second or third year of life, the best way to investigate development of the disorder involves studying infant siblings of children with ASD (High-Risk infants), who have a significantly increased risk (10- to 20-fold) of developing ASD. This study uses a neurodevelopmental approach and a variety of techniques to identify abnormalities associated with High-Risk ASD infants (ages 6 to 36 months) by tracking their development in comparison to normal infants. Abnormalities in visual processing, motion processing, face processing, and social/emotional processing will be assessed. Standardized tests will also be used to evaluate social, communicative, and cognitive skills. The hope is that these studies will shed light on the neurodevelopmental origins of ASD (and the broader autism phenotype) and aid in early diagnosis of the disorder.