Facing emotional vocalizations and instrumental sounds: Sighted and blind individuals spontaneously and selectively activate facial muscles in response to emotional stimuli

Facial mimicry of visually observed emotional facial actions is a robust phenomenon. Here, we examined whether such facial mimicry extends to auditory emotional stimuli. We also examined if participants’ facial responses differ to sounds that are more strongly associated with congruent facial movements, such as vocal emotional expressions (e.g., laughter, screams), or less associated with movements, such as non-vocal emotional sounds (e.g., happy, scary instrumental sounds). Furthermore, to assess whether facial mimicry of sounds reflects visual-motor or auditory-motor associations, we compared individuals that vary on lifetime visual experience (sighted vs. blind). To measure spontaneous facial responding, we used facial electromyography to record the activity of the corrugator supercilii (frowning) and the zygomaticus major (smiling) muscles. During measurement, participants freely listened to the two types of emotional sounds. Both types of sounds were rated similarly on valence and arousal. Notably, only vocal, but not instrumental, sounds elicited robust congruent and selective facial responses. The facial responses were observed in both sighted and blind participants. However, the muscles’ responses of blind participants showed less differentiation between emotion categories of human vocalizations. Furthermore, the groups differed in the shape of the time courses of the zygomatic activity to human vocalizations. Overall, the study shows that emotion-congruent facial responses occur to non-visual stimuli and are more robust to human vocalizations than instrumental sounds. Furthermore, the amount of life-time visual experience matters little for the occurrence of cross-channel facial mimicry, but it shapes response differentiation.