o:2963 The Joint Simon task is not joint for capuchin monkeys en Human cooperation can be facilitated by the ability to create a mental representation of one's own actions, as well as the actions of a partner, known as action co-representation. Even though other species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to investigate this action co-representation. We tested brown capuchin monkeys (Sapajus [Cebus] apella), a highly cooperative species, on a computerized Joint Simon task and found that, in line with previous research, the capuchins' performance was compatible with co-representation. However, a deeper exploration of the monkeys' responses showed that they, and potentially monkeys in previous studies, did not understand the control conditions, which precludes the interpretation of the results as a social phenomenon. Indeed, further testing to investigate alternative explanations demonstrated that our results were due to low-level cues, rather than action co-representation. This suggests that the Joint Simon task, at least in its current form, cannot determine whether non-human species co-represent their partner's role in joint tasks. Animals; Cebusphysiology; Cues 1552099 10.1038/s41598-024-55885-x 2024-05-10T09:13:16.251Z 44 yes 46 Mayte Martínez University of Veterinary Medicine Vienna / Georgia State University 0000-0002-8380-3073 Sarah F. Brosnan Georgia State University person Matthew H. Babb Georgia State University person Friederike Range University of Veterinary Medicine Vienna person 0000-0003-3127-5536 application/pdf 1780103 https://phaidra.vetmeduni.ac.at/o:2963 no yes 16 70 1552253 Scientific Reports 11 14 1 Nature Portfolio 2024