Persons with developmental disabilities have difficulties in the perception of emotion from facial cues in comparison with age-matched peers without disabilities. While such difficulties are often associated with autism, they are also reported in persons with Down syndrome and other developmental disabilities. This study will compare two populations with disabilities associated with mental retardation - autism and Down Syndrome - that show reported difficulties in emotion perception and compare them with mental age-matched children who have exhibited typical development. The research will evaluate stimulus control in facial stimuli using several methods, including discrimination training, eye-tracking, and electrophysiology. The ultimate research goal is translational and pointed toward the possibility that deficits in emotion recognition from facial cues may be correctable, in whole or in part, via training.