Guillaume Dezecache, Laurence Conty, Michele Chadwick, Leonor Philip, Robert Soussignan, Dan Sperber, Julie Grèzes

Little is known about the spread of emotions beyond dyads. Yet, it is of importance for explaining the emergence of crowd behaviors. Here, we experimentally addressed whether emotional homogeneity within a crowd might result from a cascade of local emotional transmissions where the perception of another's emotional expression produces, in the observer's face and body, sufficient information to allow for the transmission of the emotion to a third party. We reproduced a minimal element of a crowd situation and recorded the facial electromyographic activity and the skin conductance response of an individual C observing the face of an individual B watching an individual A displaying either joy or fear full body expressions. Critically, individual B did not know that she was being watched. We show that emotions of joy and fear displayed by A were spontaneously transmitted to C through B, even when the emotional information available in B's faces could not be explicitly recognized. These findings demonstrate that one is tuned to react to others' emotional signals and to unintentionally produce subtle but sufficient emotional cues to induce emotional states in others. This phenomenon could be the mark of a spontaneous cooperative behavior whose function is to communicate survival-value information to conspecifics.