A study conducted by researchers from Jean Monnet University and the University of Saint-Etienne has discovered that the sound of a baby crying, especially those indicative of pain, can cause a noticeable increase in facial temperature among adults. This physiological response may serve as an evolutionary mechanism to prompt caregivers into action.
The research, published in the Journal of the Royal Society Interface, highlights how a baby’s cries convey distress—specifically, cries that signal pain are designed to be more chaotic and attention-grabbing than those of mere discomfort. Infants lack the ability to express their needs through language, so their cries become critical signals for caregivers.
Scientists observed that cries associated with high levels of distress create unique sound patterns known as nonlinear phenomena (NLPs). These sounds are produced when an infant forcefully contracts their ribcage, generating bursts of air through their vocal cords that create variable pitches and disharmonious sounds. According to Lény Lego, a bioacoustician at Jean Monnet University, “It has been established that NLPs are reliable markers of the level of distress and/or pain expressed by the baby.”
The study involved 41 participants, consisting of 21 men and 20 women, with an average age of 35. They listened to a selection of 23 audio recordings from 16 different infants, capturing cries during both benign situations—such as bath time—and painful experiences, like receiving a vaccination. As the participants listened, a thermal camera monitored their facial temperatures.
Changes in facial temperature are indicative of the autonomic nervous system’s response, which operates largely below conscious awareness and regulates essential body functions such as heart rate and breathing. After listening, participants were asked to report whether they perceived the sounds as expressions of discomfort or pain.
The findings revealed that higher levels of NLP in a baby’s cry resulted in a more significant increase in facial temperature among listeners. The data suggests that these chaotic cries are significantly more effective at capturing adult attention on a physiological level compared to cries with minimal NLP. Notably, both male and female participants demonstrated similar thermal responses, reinforcing previous research indicating that individuals of all genders can reliably discern pain in a baby’s cry.
While the study’s results are compelling, the authors caution that it remains preliminary. They point out that the participants had limited experience with infants, which may not accurately represent the physiological responses of seasoned caregivers. Future research could explore how experience with babies influences physiological reactions to NLPs in cries.
The researchers also note that the cries analyzed in this study were natural sounds, full of diverse acoustic characteristics. They have yet to determine which specific aspects of NLPs elicit a thermal response or if it is the unsettling combination of these sounds that creates such a powerful signal for help.
This innovative research sheds light on the connection between our physiological responses and the sounds that infants make, illustrating a complex interaction that may have significant implications for understanding caregiver instincts and responses to distress signals.
