One of the most compelling features of Williams syndrome (WS) is the distinctive social profile that holds promise for understanding the underlying neurogenetic systems that provide meaning to human social interaction. Our studies to date suggest that while individuals with WS typically demonstrate an increased appetitive social drive, the social profile is characterized by dissociations (e.g., overly-friendly with a difficulty in making friends;socially fearless but anxious;positive affect with maladaptive behaviors). The aims of Project V focus on the characterization of the social phenotype of WS, enabling links to the genetic and neurobiological pathways of these "dissociations". To this end, the Specific Aims are: Aim 1: Insatiable Appetitive Drive for Approaching Strangers will examine the underpinnings and variability of the increased attraction and approachability towards unfamiliar people observed in individuals with WS. Aim 2: The Unique Salience of Faces will elucidate the nature and underlying mechanisms of the atypically high interest in faces in WS, and its relation to the resultant "hypersocial" phenotype. Aim 3: Unusual Emotional Sensitivity will investigate both (a) the perception and processing of affect of others by those with WS, and (b) the overall affective style of individuals with WS. Using a multi-method design reflecting multiple levels of explanation (electrophysiology, autonomic function, and eye fixation). Project V studies will produce highly nuanced, quantifiable and independent key dimensions of the unique social behavior characteristic of WS. From a theoretical standpoint, a major thrust of the proposed work is to disentangle the processing of key components of social interaction and their respective underpinnings in the context of the enigmatic, yet paradoxical, WS social phenotype, with the ultimate goal of characterizing the complete system of social behavior and understanding the ways it can break down. Such a multileveled approach has not been previously adopted within this domain of inquiry. Results from these studies will add unique knowledge to our understanding of social behavior, by further defining the pathways implicated in gene-brain-behavior linkages, and are designed to contribute to better-informed treatments.