Infants spend most of their time looking at, and interacting with, other people. In natural scenes, typically developing infants’ attention is strongly drawn to familiar or friendly people, and to human faces, eyes and hands. By contrast, infants at high risk for Autism Spectrum Disorders (ASD) show disruptions in these very early signatures of social attention. Differences in early social attention may be critical to the developmental course of ASD, because where infants direct their attention determines both their social interactions and their opportunities for learning. However, the mechanisms driving infants’ social attention are poorly understood. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging method that can measure blood flow related to neural activity in awake infants sitting on their parents’ laps. We propose to use fNIRS to test two possible drivers of social attention: do infants pay more attention to people (or parts of people, such as eyes) because they “like” them (i.e. find them rewarding) or because they are more “interesting” (i.e. a better source of novel information)? Do each of these mechanisms drive social attention under different circumstances or for different aspects of the social world?