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

Disgust and fear are emotions that evolved to address different types of threats: pathogens and predators, respectively. Yet the cognitive mechanisms underlying disgust remain poorly understood, particularly in non-human animals. We investigated how pathogen- and predator-related stimuli influence cognition in captive chimpanzees (Pan troglodytes), using touchscreen and eye-tracking tasks. In three experiments, subjects performed a number ordering task while exposed to images (e.g., carcasses, rotten food, invertebrates, snakes) or odors (e.g., of organic decomposition, emesis). Pathogen-related stimuli, particularly those linked to organic decomposition and fermentation, modulated performance in distinct temporal patterns, reducing accuracy and later disrupting efficiency upon re-exposure. In contrast, predator images enhanced performance by reducing response latencies. A fourth eye-tracking experiment further showed that both carcass and snake images captured and held attention. Overall, our results suggest distinct cognitive signatures for pathogen-versus predator-related threats in chimpanzees, offering insight into the evolution of defensive emotions.