Comparing the Performances of Chimpanzees (Pan troglodytes) and Gorillas (Gorilla gorilla gorilla) in Two Self-Awareness Tasks.

Self-awareness has most commonly been studied in nonhuman animals by implementing mirror self-recognition (MSR) tasks. The validity of such tasks as a stand-alone method has, however, been debated due to their high interindividual variation (including in species deemed self-aware like chimpanzees), their reliance on only one sensory modality, their discrete outcomes (i.e., pass/fail) and, in general, questionned regarding their ability to assess self-awareness. Therefore, a greater variety of methods that assess different aspects of the self, while simultaneously contributing to a more gradualist view of self-awareness, would be desirable. One such method is the body-as-obstacle task (BAO), testing for another dimension of body self-awareness. The ability to understand one's own body as an obstacle to the completion of a desired action emerges in young children at approximately the same age as mirror self-recognition, suggesting a shared mental representation. Whereas recently some studies showed body self-awareness in nonhuman animals, so far, outside of children no studies have compared how the performances of individuals relate between these two tasks. Therefore, here we study both a MSR and a BAO task in chimpanzees and gorillas. We chose these species particularly because evidence for MSR in chimpanzees is well established, whereas results for gorillas have been mixed, which has been attributed to the study design of MSR tasks, and for which a BAO task might thus provide more conclusive evidence. We find that although only some chimpanzees showed evidence for mirror self-recognition, thus replicating previous findings on interspecies differences in MSR, chimpanzees and gorillas performed equally well in the BAO task. Yet, we further found no correlation between the individuals' performances in both tasks. We discuss the implications of these findings for the interpretation of the results of BAO tasks as a possible alternative paradigm for the study of self-awareness in non-human animals.