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…

Recognizing relational similarity relies on the ability to understand that defining object properties might not lie in the objects individually, but in the relations of the properties of various object to each other. This aptitude is highly relevant for many important human skills such as language, reasoning, categorization and understanding…

There is currently much controversy about which, if any, mental states chimpanzees and other nonhuman primates understand. In the current two studies we tested both chimpanzees' and human children's understanding of both knowledge-ignorance and false belief--in the same experimental paradigm involving competition with a conspecific. We found that…

Human infants imitate others' actions "rationally": they copy a demonstrator's action when that action is freely chosen, but less when it is forced by some constraint (Gergely, Bekkering & Kiraly, 2002). We investigated whether enculturated chimpanzees (Pan troglodytes) also imitate rationally. Using Gergely and colleagues' (2002) basic procedure,…

Compared comprehension of novel communicative signs to assist 2.5- and 3-year-old humans, chimpanzees, and orangutans find hidden objects during a hiding-finding game. Found that children at both ages performed above chance with all signs. No ape performed above chance for any signs not known before the experiment despite three times as many…