Ew! Yuck! Ugh! – Nonverbal Vocalisations of Pathogen and Moral Disgust

Nonverbal vocalisations 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 vocalisations of pathogen and moral disgust are acoustically distinct and whether listeners can differentiate between them. We conducted machine learning analyses of acoustic parameters and two preregistered listening experiments (all conducted in 2023) to test these questions. Based on a dataset of 1000 spontaneous disgust vocalisations, six machine learning classifiers with 5-fold cross-validation were able to accurately distinguish between pathogen and moral disgust vocalisations (AUC = 0.73). In a listening experiment (n = 200), participants differentiated between the two types of disgust vocalisations above chance levels. In a second listening study (n = 680), listeners rated pathogen disgust vocalisations as expressing stronger avoidance motivations in the expresser and as sounding more negative than moral disgust vocalisations. Together, these findings demonstrate that pathogen and moral disgust vocalisations are both acoustically and perceptually distinct. These findings align with the putative functional differences between pathogen and moral disgust.