Human freezing responses to virtual characters in immersive virtual reality are impacted by body expression, group affiliation and threat proximity

Social threat requires fast adaptive reactions. One prominent threat-coping behavior present in humans is freezing, of which heart rate deceleration and reduced postural mobility are two key components. Previous studies focused mainly on freezing reactions in rodents, but now virtual reality offers unique possibilities for controlled and ecologically valid lab-based experiments. Using immersive virtual reality, this study examined how several understudied aspects of social threat, i.e., emotional body expressions, group affiliation, and distance from the potential threat, affect freezing behavior in humans. Reduced heart rate and postural mobility were observed in participants when they faced aggressive-looking and proximal avatars. Freezing was also observed for ingroup aggression when participants were embodied in a black-skinned virtual body and faced black-skinned aggressive and proximal avatars. Our results, based on a highly ecological virtual reality paradigm, provide novel evidence on the social factors that elicit freezing behavior in humans.