Chimpanzees coordinate interrogative markers to ask questions

Abstract Questions serve to initiate and continue conversation as well as to gain information and introduce new topics. In signed languages a question can be signaled by modifying the content of an utterance or by coordinating the use of nonmanual markers (e.g., the questioning look) and manual modulation (e.g., holding the sign for an extended duration). Cross-fostered chimpanzees, who use signs of American Sign Language (ASL), have demonstrated behaviors that appear in human conversation, including question-answer exchanges. The current study describes the production of questions by signing chimpanzees in a conversational context and offers a methodology for quantifying the relationship between nonmanual markers and manual modulation involved in interrogative utterances.