Rivas, E. (2005). Recent use of signs by chimpanzees (Pan troglodytes) in interactions with humans. Journal of Comparative Psychology, 119(4), 404-417.

In light of the controversy about the linguistic properties of chimpanzee signing behavior, the recent sign use of 5 chimpanzees (Pan troglodytes) with long histories of sign use was analyzed while they interacted with longtime human companions. Four corpora from 1992 to 1999 consisting of 3,448 sign utterances were examined. The chimpanzees predominantly used object and action signs. There was no evidence for semantic or syntactic structure in combinations of signs. Longer combinations showed repetition and stringing of object and action signs. The chimpanzees mostly signed with an acquisitive motivation. Requests for objects and actions were the predominant communicative intentions of the sign utterances, though naming and answering also occurred. This recent sign use shows multiple differences with (early) human language...... ..........the conclusion for now on chimpanzee signing is that the chimpanzees do not use signs in the way human children use language but have mostly found signs to be useful instruments to get what they want when interacting with a human.