Children with autism spectrum disorders share a pervasive impairment in the development of reciprocal social interaction skills but vary in their verbal and nonverbal communication skills and various restricted and repetitive behaviors. This variability presents challenges for developmental and neurobiological models. Our understanding of the autism spectrum disorders is improved by studying children at various points in development, including infants, and by using a careful neuropsychological approach. This approach is emphasized here in studies that examine characteristics of infants...