Contingency in requests of signing chimpanzees (Pan troglodytes)

Conversational interactions depend on partners making contingent responses. This experiment examined the responses of five chimpanzees (Pan troglodytes), Washoe, Moja, Tatu, Dar and Loulis, to four conversational conditions. Following the chimpanzee’s request, a human interlocutor either: (1) complied with the request, (2) provided an unrequested item or activity, (3) refused to comply or (4) did not respond to the request. The chimpanzees’ responses were contingent on the conversational input of the interlocutor. When their requests were satisfied, the chimpanzees most often ceased signing. However, when their requests were misunderstood, refused or not acknowledged, the chimpanzees repeated and revised. This pattern of responses is comparable to patterns of conversational responses in human children. Keywords: chimpanzees; American Sign Language; requests; pragmatics; conversation; gesture; communication; Pan troglodytes