Although apes understand others' goals and perceptions, little is known about their understanding of others' emotional expressions. We conducted three studies following the general paradigm of Repacholi and colleagues (1997, 1998). In Study 1, a human reacted emotionally to the hidden contents of two boxes, after which the ape was allowed to…

Recent research suggests that witnessing events of fission (e.g., the splitting of a solid object) impairs human infants', human adults', and non-human primates' object representations. The present studies investigated the reactions of gorillas and orangutans to cohesion violation across different types of fission events implementing a behavioral…

A nonverbal false belief task was administered to children (mean age 5 years) and two great ape species: chimpanzees ("Pan troglodytes") and bonobos ("Pan paniscus"). Because apes typically perform poorly in cooperative contexts, our task was competitive. Two versions were run: in both, a human competitor witnessed an experimenter hide a reward in…

A milestone in human development is coming to recognize that how something looks is not necessarily how it is. We tested appearance-reality understanding in chimpanzees ("Pan troglodytes") with a task requiring them to choose between a small grape and a big grape. The apparent relative size of the grapes was reversed using magnifying and…

G. Gergely, H. Bekkering, and I. Kiraly (2002) showed that 14-month-old infants imitate rationally, copying an adult's unusual action more often when it was freely chosen than when it was forced by some constraint. This suggests that infants understand others' intentions as rational choices of action plans. It is important to test whether apes…

Developmental research suggests that whereas very young infants individuate objects purely on spatiotemporal grounds, from (at latest) around 1 year of age children are capable of individuating objects according to the kind they belong to and the properties they instantiate. As the latter ability has been found to correlate with language, some…

Four bonobos, seven gorillas, and six orangutans were presented with two small rectangular boards on a platform. One of the boards had a piece of food under it so that it acquired an inclined orientation whereas the other remained flat on the platform. Subjects preferentially selected the inclined board. In another experiment, subjects were…

The study investigates what an intermediate success rate means in bonobos, chimpanzees, and orangutans. Apes participated in liquid conservation experiments where they had to track the larger of two different quantities of juice after various kinds of transformations [Suda, C., & Call, J. (2004). Piagetian liquid conservation in the great apes…