Lurz, R. W., Krachun, C., Mareno, M. C., & Hopkins, W. D. (2022). Do chimpanzees predict others' behavior by simulating their beliefs? Animal Behavior and Cognition, 9(2), 153-175. https://doi.org/10.26451/abc.09.02.01.2022

Recent studies have shown that great apes predict that other agents will search for objects of interest where the agents believe the objects are hidden. Little is understood about the cognitive process that apes undergo to make such predictions. According to prevailing models, great apes make such predictions by metarepresenting others’ beliefs or perceptual states. We investigated the simpler simulation model. In this model, apes predict where other agents will search for objects of interest by simulating believing what another agent believes about the location of the object. The simulation model predicts that simulating what another believes should manifest in altercentric biasing effects, such as behaving as if one shares another’s belief in cases where the other’s belief is false. We tested this by giving chimpanzees a novel search paradigm embedded in a change-of-location false-belief test and measured where they searched for a grape that they witnessed moved from its original location to a new location. In true-belief trials, chimpanzees were presented with an agent who knew (as they did) that the grape was hidden in the new location; in false-belief trials, the agent falsely believed the grape was still hidden in the original location while the chimpanzee knew it was hidden in the new location. As predicted by the simulation model, chimpanzees searched for the grape closer to its original location than to its new location in significantly more false-belief trials than true-belief trials. Results suggest that chimpanzees show a signature altercentric biasing effect of simulating believing what others believe and may use simulation, rather than metarepresentation, to predict where others will search for objects of interest.