Social traits and facial information : behavioral and neuronal evidence within the framework of phylogenetic and clinical studies

Faces provide a complex set of physical, emotional and social information to the observer that determines how people will interact with others. From facial information, human subjects can form rapid, first impression judgments. The ability to create social judgments from faces is the core topic of this work. This thesis will focus on how social information and trust is spontaneously detected from faces. In my studies I used eye tracking procedure, electrophysiology (EEG) and behavioral measures. In a first experiment, I investigated the evolutionary origin of trustworthiness detection testing whether monkeys (Macaca Mulatta and Fascicularis) have a spontaneous preference towards trustworthy human faces, thus suggesting a capacity to detect facial cues similar to those used by humans. Using a preference visual paradigm we observed that both species spent more time looking at trustworthy faces than untrustworthy ones. I further conducted three studies with patients affected by Williams-Beuren syndrome (WS). This pathology can be considered a neurobiological human model for the overexpressed social behavior. Are Williams-syndrome patients able to detect trustworthiness from faces? How WS patients form the representation of trustable faces ? Using a preference visual paradigm I observed that WS patients looked less the trustworthy faces compared to control group. This implicit behavior supports patients’ tendency to trust everybody. In a second experiment using reverse correlation paradigm - the procedure pushes subjects to select from noise the facial features that they believe are important for a specific judgment – I found that at group level patients did not show a stereotypical image of trustworthy faces compared to healthy controls. In a final study I investigate whether electrophysiological brain sources, with particular attention to the source localized in the superior temporal sulcus, could explain patients’ behaviour. I found that the activity of a source localized in the STS at 240ms was significantly modulated by eye proximity as in the control group. Overall the results of this work suggests the presence of a fast route in the brain that plays the fundamental role of modulating approach/avoidance behavior. This route may be altered in patients characterized by an overexpressed social behavior