Nonlinear acoustic phenomena tune the adults' facial thermal response to baby cries with the cry amplitude envelope.

Getting caregivers to respond to their pain cries is vital for the human baby. Previous studies have shown that certain features of baby cries-the nonlinear phenomena (NLP)-enable caregivers to assess the pain felt by the baby. However, the extent to which these NLP mobilize the autonomic nervous system of an adult listener remains unexplored. Here, we show that variations in a listener's facial temperature, a marker of the autonomic emotional response, reflect the pain expressed by a baby's cry. Specifically, by conducting listening experiments with cries expressing mild discomfort or acute pain, we demonstrate that NLP modulate the facial thermal response in adult listeners, irrespective of sex and of cry pitch variation. The temporal dynamics of the thermal response is more closely synchronized with the amplitude envelope of the acoustic signal when listening to a cry containing a large level of NLP than when NLP are less prominent. The pain encoded in a baby's cry thus generates a synchronized emotional response in both adult men and women, emphasizing that our ability to decode the information carried by babies' cries integrates an immediate activation of the autonomic nervous system before engaging higher-order cognitive processes.