CROWD. STRESS. NEED FOR SPACE. PSYCHOPHYSIOLOGICAL RESPONSES TO SALIENT SOCIAL ENVIRONMENTS: FROM SOCIAL ANXIETY TO EXTREME SOCIAL WITHDRAWA

Social interactions are fundamental to human functioning, yet social environments can be experienced very differently across individuals. Social anxiety can alter the perception of others, increasing perceived evaluation and physiological arousal to social cues. When interactions become difficult to manage, avoidance may serve as a strategy to reduce stress. At its extreme, disengagement from social life characterizes Extreme Social Withdrawal (ESW), a growing condition that has attracted increasing research attention. However, previous studies have primarily focused on its psychopathological correlates and behavioral characteristics, leaving real-time responses to social cues largely unexplored. This thesis investigated responses to socially salient environments across Typically Developing (TD), Social Anxiety (SA) and ESW participants. In three studies, participants were immersed in a virtual subway station in which crowd proximity and emotional expressions were systematically manipulated. Selfreported stress, electrodermal activity (EDA), avoidance behavior, and gaze were combined to examine both overall responses to the social environment and transient responses to specific social events. Study one examined individual differences in social anxiety in a nonclinical sample. Higher anxiety was associated with greater perceived stress and increasingly context-dependent physiological and behavioral responses. Notably, social anxiety did not substantially alter the frequency of face contacts but modulated their accompanying physiological response, suggesting that similar overt engagement may coexist with different levels of autonomic activation. Study two compared adolescents with ESW and TD peers. ESW participants reported greater stress and showed more frequent phasic EDA fluctuations. Differences were particularly evident around discrete social events. ESW participants showed reduced spontaneous social exploration and initiated fewer face contacts, while responding more frequently when social attention was directed toward them. Externally initiated social events were also associated with a reduction in phasic EDA compatible with a more inhibited, freeze-like response. Study three directly compared ESW with individuals showing comparable levels of social anxiety. The groups showed substantial overlap in subjective and physiological responses, suggesting that some components of autonomic responsivity may be shared across SA and ESW. Differences remained, however, in the behavioral organization of social engagement, particularly in spontaneous exploration and in how gaze exchanges were initiated and reciprocated. Together, these findings show that social withdrawal cannot be understood from a single level of response, nor as a simple amplification of social anxiety. Instead, they appear to share some aspects of sensitivity to socially 4 demanding environments while differing in how this sensitivity is translated into behavior. A better characterization of how individuals with ESW respond to social interactions may advance our understanding of this rapidly growing phenomenon. Ultimately, this knowledge may contribute to identify tailored interventions that could help individuals with ESW re-engage with social interactions and benefit from contact with others