Returning a smile: Initiating a social interaction with a facial emotional expression influences the evaluation of the expression received in return.

Face-to-face social interactions are characterized by the reciprocal exchange of facial emotions between interaction partners. Typically, facial emotional expressions have been studied in passive observation paradigms, while interactive mechanisms remain unknown. In the current study we investigate how sending a facial emotional expression influenced the evaluation of an emotional expression received in return. Sixty-eight participants were cued to direct a facial emotional expression (happy, angry, neutral) towards a virtual agent in front of them. The virtual agent then responded with either the same or another emotional expression (happy, angry). Evaluation of the response expressions was measured via ratings of valence and arousal as well as EMG recordings of the M. corrugator supercilii and the M. zygomaticus major. Results revealed a significant interaction between the emotion of the initial facial expression and the response expression. Valence of happy response expressions were increased when participants had initially displayed a smile compared to a neutral expression or a frown. This was also reflected in the EMG responses. Initiating an interaction with a smile increased Zygomaticus activation for happy relative to angry response expressions compared to when the interaction was initiated with a frown. In contrast, no interplay of the initial and the response expression was observed in the Corrugator. These findings demonstrate that smiling or frowning at another person can modulate socio-emotional processing of subsequent social cues. Therefore, the present study highlights the interactive nature of facial emotional expressions.