Vocal and gestural responses of cross-fostered chimpanzees

Ten positive, five neutral, and five negative events were presented to two chimpanzees, Tatu (female, 64 months old) and Dar (male, 56 months old), who had been cross-fostered from birth by human beings. Each event was announced in American Sign Language 10 s before. The announcements and events were common items in the cross-fostering routines and were administered according to a balanced design over a period of 2 months. Vocal and signed responses to the announcements and to the events were recorded. The likelihood of either mode of response depended on affective charge, and the likelihood of vocal and signed responses was positively correlated. Signed responses were more likely than vocal responses; signed responses were more likely to be evoked by announcements than by events, whereas vocal responses were more likely to be evoked by events than by announcements. The type of vocal response depended on the affective charge and on whether the response was immediate (to the event) or anticipatory (to the announcement). Incorporation of signs and phrases from the announcements, and reiteration of signs and phrases within an utterance depended on affective charge, just as they do for human children.