Ew! Yuck! Ugh! Nonverbal vocalizations of pathogen and moral disgust

Nonverbal vocalizations like "Ew!" and "Ugh!" are often used to communicate disgust. While disgust evolved primarily to promote the avoidance of pathogens (pathogen disgust), it is also expressed toward moral violations (moral disgust). In this study, we investigated whether vocalizations of pathogen and moral disgust are acoustically distinct and whether listeners can differentiate between them. To do so, we conducted machine learning analyses of acoustic parameters and two preregistered listening experiments (all conducted in 2023). Based on a data set of 1,000 spontaneous disgust vocalizations, six machine learning classifiers with fivefold cross-validation were able to distinguish between pathogen and moral disgust vocalizations with above-chance accuracy (AUC = 0.73). In a listening experiment (n = 200), participants differentiated between the two types of disgust vocalizations above chance (62%). In a second listening study (n = 680), listeners rated pathogen disgust vocalizations as expressing stronger avoidance motivations and as sounding more negative than moral disgust vocalizations. Together, these findings demonstrate that pathogen and moral disgust vocalizations are both acoustically and perceptually distinguishable. These findings align with the putative functional differences between pathogen and moral disgust.