The primary objective of this research study is to provide preliminary answers to the question: "What are the mechanisms by which early intervention improves outcomes in autism?" In this study, researchers will use eye-tracking methodology to assess neurocognitive markers of treatment response in young children with autism receiving intensive in-home treatment as part of an Ongoing randomized controlled trial (RCT). The study will leverage an Ongoing NIH-funded RCT of the Early Start Denver Model (ESDM), a relationship-based behavioral intervention focused on building social motivation using positive emotional feedback with a developmental curriculum. Recent research suggests that the ESDM results in significant intellectual, language, and social improvement in young toddlers with autism. The proposed study will use eye-tracking to measure a number of social information processing variables that are conceptually tied to the core deficits targeted by the ESDM, such as social orienting, social attention, and emotion understanding. This study will compare neurocognitive processing differences between the treatment group and a community control group at outcome in order to find neurocognitive correlates of treatment response. A third independent group of typical children will be recruited and tested to provide a normal comparison point for evaluating clinical significance of group differences in eye-tracking measures. This study will provide important knowledge about the potential mechanisms and correlates of treatment change. Understanding mechanisms of change is particularly important because it can lead to further refinements in the way treatment is designed and administered, modifying aspects of treatment that do not relate to underlying mechanisms while enhancing those aspects of treatment that do appear related to change.