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This research was supported by the European Research Council under the European Union's Seventh Framework Program ( FP7/2007-2013 )/ERC grant agreement no 609819, SOMICS. ; Humans can tell when they find a task difficult. Subtle uncertainty behaviors like changes in motor speed and muscle tension precede and affect these experiences. Theories of animal metacognition likewise stress the importance of endogenous signals of uncertainty as cues that motivate metacognitive behaviors. However, while researchers have investigated second-order behaviors like information seeking and declining difficult trials in nonhuman animals, they have devoted little attention to the behaviors that express the cognitive conflict that gives rise to such behaviors in the first place. Here we explored whether three chimpanzees would, like humans, show hand wavering more when faced with more difficult choices in a touch screen transitive inference task. While accuracy was very high across all conditions, all chimpanzees wavered more frequently in trials that were objectively more difficult, demonstrating a signature behavior which accompanies experiences of difficulty in humans. This lends plausibility to the idea that feelings of uncertainty, like other emotions, can be studied in nonhuman animals. We propose to routinely assess uncertainty behaviors to inform models of procedural metacognition in nonhuman animals. ; Publisher PDF ; Peer reviewed

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy through EXC 2025/1 "Matters of Activity (MoA)" and by the "The Sound of Meaning (SOM)", Pu 97/22-1,"Brain Signatures of Communication (BraSiCo)", Pu 97/23-1, and "Phonological Networks (PhoNet)", Pu 97/25-1. K.M. was supported by the Berlin School of Mind and Brain and by the Onassis foundation. M.A was supported by the "SOMICS" ERC Synergy grant (nr.609819). M.B was supported by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 749229. ; Theories on the evolution of language highlight iconicity as one of the unique features of human language. One important manifestation of iconicity is sound symbolism, the intrinsic relationship between meaningless speech sounds and visual shapes, as exemplified by the famous correspondences between the pseudowords 'maluma' vs. 'takete' and abstract curved and angular shapes. Although sound symbolism has been studied extensively in humans including young children and infants, it has never been investigated in non-human primates lacking language. In the present study, we administered the classic "takete-maluma" paradigm in both humans (N = 24 and N = 31) and great apes (N = 8). In a forced choice matching task, humans but not great apes, showed crossmodal sound symbolic congruency effects, whereby effects were more pronounced for shape selections following round-sounding primes than following edgy-sounding primes. These results suggest that the ability to detect sound symbolic correspondences is the outcome of a phylogenetic process, whose underlying emerging mechanism may be relevant to symbolic ability more generally. ; Publisher PDF ; Peer reviewed

This research was supported by the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013) / ERC grant agreement n° [609819], SOMICS. ; Recent years have seen a growing interest in the question of whether and how groups of nonhuman primates coordinate their behaviors for mutual benefit. On the one hand, it has been shown that chimpanzees in the wild and in captivity can solve various coordination problems. On the other hand, evidence of communication in the context of coordination problems is scarce. Here, we investigated how pairs of chimpanzees (Pan troglodytes) solved a problem of dynamically coordinating their actions for achieving a joint goal. We presented five pairs of chimpanzees with a turn-taking coordination game, where the task was to send a virtual target from one computer display to another using two touch-screens. During the joint practice of the game some subjects exhibited spontaneous gesturing. To address the question whether these gestures were produced to sustain coordination, we introduced a joint test condition in which we simulated a coordination break-down scenario: subjects appeared either unwilling or unable to return the target to their partner. The frequency of gesturing was significantly higher in these test trials than in the regular trials. Our results suggest that at least in some contexts chimpanzees can exhibit communicative behaviors to sustain coordination in joint action. ; Publisher PDF ; Peer reviewed

This work was supported by the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC grant agreement no. 609819, SOMICS and Templeton World Charity Foundation, grant ID: TWCF0314. ; Almost all animals navigate their environment to find food, shelter, and mates. Spatial cognition of nonhuman primates in large-scale environments is notoriously difficult to study. Field research is ecologically valid but controlling confounding variables can be difficult. Captive research enables experimental control, but space restrictions can limit generalizability. Virtual reality technology combines the best of both worlds by creating large-scale, controllable environments. We presented six chimpanzees with a semi naturalistic virtual environment, using a custom touch screen application. The chimpanzees exhibited signature behaviors reminiscent of real-life navigation: they learned to approach a landmark associated with the presence of fruit, improving efficiency over time; they located this landmark from novel starting locations, and approached a different landmark when necessary. We conclude that virtual environments can allow for standardized testing with higher ecological validity than traditional tests in captivity, and harbor great potential to contribute to longstanding questions in primate navigation, e.g., the use of landmarks, Euclidean maps, or spatial frames of reference. ; Publisher PDF ; Peer reviewed