Human social interaction relies fundamentally on the ability to express and perceive affective states through action. According to Daniel Stern’s concept of Vitality Forms (VFs), actions convey affective qualities, such as gentleness or rudeness, shaping how people behave beyond their action goal. While previous research has shown that VFs expressed by agents can influence observers’ perception and their motor responses, evidence from real, face-to-face social interactions remains limited. The present study addresses this gap by examining how affective contagion mediated by VFs operates during an authentic social exchange. Specifically, this work aims to: 1) identify the kinematic parameters that are influenced by others during a real game interaction; 2) determine whether this contagion effect is conscious or automatic; 3) examine whether this effect is associated with participants’ empathy abilities. In this view, pairs of participants engaged in a tic-tac-toe game, with one player acting as an insider instructed to consistently display either gentle or rude behavior through their action execution. Across 18 matches, the action of both players were recorded to assess whether and how the VFs of the inside player modulated the participant’s motor response in terms of kinematics. At regular intervals, participants reported their own affective state and their perception of the insider’s affect using Likert scales. Moreover, to assess individual empathic abilities, the Empathy Quotient questionnaire was administered. The findings revealed three principal results. First, participants’ actions were significantly modulated by the VFs of the inside player across multiple kinematic parameters (i.e., velocity, acceleration etc.), indicating a clear motor contagion effect. Second, although participants accurately perceived changes in the insider’s attitude, they did not report corresponding changes in their affective state, suggesting that VFs contagion occurs implicitly and without conscious awareness. Third, the magnitude of this motor contagion was positively correlated with empathic abilities of participants.
Carapelli et al. (Tue,) studied this question.