Paying attention to communicative faces is essential for our understanding of the social world. Indeed, faces provide observers rich and complex information about the identity (gender, age, etc), the socio-emotional state (eye-brows movements, eye-gaze) and the linguistic message (auditory speech sounds/mouth movements) of our social partners. The aim of this research project is to understand how infants with Prader-Willi Syndrome perceive communicative faces from their first months of life. We hypothesize that the general lack of alertness observed at birth might prevent infants with PWS to benefit from communicative faces as much as normal-developing babies. Later on in their life, these early impairments coud contribute to their immature social and emotional behaviors. This project will allow us to characterize these abilities and then, more importantly, to develop adapted rehabilitation methods, intervening since the first month of life, to stem the development of further social and cognitive impairments later on. Crucially, this study will be the first building block to develop new therapeutic approaches for the treatment of socio-cognitive symptoms associated with PWS. This research could thus directly impact the social life of individuals with PWS.