for skepticism are the differences in ease with which human beings and apes can learn language; there are also questions of whether there is a clear beginning and end to the signed gestures and whether the apes actually understand language or are simply doing a clever trick for a reward. While vocabulary words from American Sign Language are used to train the apes, native users of ASL may note that mere knowledge of ASL's vocabulary does not equate to knowledge of ASL. See also Alex (parrot) Animal cognition Animal communication Animal language Animal training Biosemiotics Human-animal communication Language – as it pertains to humans Language acquisition Operant conditioning Origin of language Primate cognition Proto-language (glottogony) Theory of mind Yerkish Researchers Roger Fouts Francine Patterson David Premack Sue Savage-Rumbaugh Research subjects Ai (chimpanzee) Chantek (orangutan) Kanzi (bonobo) Lana (chimpanzee) Koko (gorilla) Lucy (chimpanzee) Nim Chimpsky (chimpanzee) Panbanisha (bonobo) Sarah (chimpanzee) Washoe (chimpanzee) Viki (chimpanzee) Notes References External links GaTech.edu – "Animal Communication" (from the book Language Files, Sixth Edition), editors: Stefanie Jannedy, Robert Poletto, Tracey L. Weldon, Department of Linguistics Ohio State University (1994) Great Ape Trust - "Use of Human Languages by Captive Great Apes" from the book World Atlas of Great Apes and Their Conservation'' by Duane Rumbaugh, Sue Savage-Rumbaugh and William Fields (2005) Thailand tree apes use song as warning Orangutans mime to get message across Animal intelligence Ethology Human–animal communication