Dissecting disgust and fear in chimpanzees: From facilitation to disruption of cognitive processes

Abstract

Disgust and fear are defensive emotions that evolved to address different types of threat. Disgust reduces pathogen exposure through avoidance, whereas fear promotes vigilance and escape from predators. While cognitive mechanisms of fear have been extensively studied, those underlying disgust remain less understood, particularly in nonhuman animals. We examined how cues of disease and predation risk influence cognitive processes in captive chimpanzees (Pan troglodytes). In three touchscreen experiments, subjects performed a number ordering task while exposed to disgust-related images (carcasses, rotten food, disease-associated invertebrates), pathogen-related odors (cadaverine, butyric acid) or fear-related images (snakes). Task performance was assessed via accuracy (proportion of correct trials), reactivity (latency to touch the first numeral), and efficiency (latency to complete trials). We found that disgust cues - particularly those related to body decomposition and food spoilage - modulated task performance in distinct temporal patterns. Carcass images reduced accuracy relative to invertebrate images and slowed performance compared to snake images, while butyric acid - and to a lower extent cadaverine - initially facilitated but later disrupted efficiency upon re-exposure. In contrast, snake images enhanced performance by reducing latencies. To test whether these effects reflected differences in visual attention, we conducted a fourth eye-tracking experiment with new carcass and snake images. Both types of stimuli captured and held attention, partly echoing human data showing sustained attention to snakes but typically not to disgust images. Overall, our results reveal distinct cognitive signatures of disgust and fear in chimpanzees, offering comparative insight into the evolution of defensive emotions. Significance statementDisgust and fear are fundamental emotions that evolved to protect organisms from distinct kinds of threats - disease and predation - but their effects on cognition have rarely been compared, especially in nonhuman animals. In this study, we examined how chimpanzees respond to pathogen-and predator-related cues using touchscreen and eye-tracking experiments. We found that pathogen cues influenced cognitive performance in complex, time-dependent ways, sometimes enhancing and later disrupting it, while predator cues consistently improved performance. Both types of stimuli captured and held attention, although sustained attention to pathogen cues was unexpected. These findings reveal distinct emotional and cognitive signatures of disgust and fear, shedding light on the evolutionary roots of how emotions shape behavior and attention.