Call, Josep Department of Developmental and Comparative Psychology, Max Planck Institute for Evolutionary Anthropology, Max Planck Society;
Call, J. (2001). Object permanence in orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes), and children (Homo sapiens). Journal of Comparative Psychology, 115(2), 159-171. doi:10.1037/0735-7036.115.2.159.