Linguistically mediated tool use and exchange by chimpanzees (Pan troglodytes)

Abstract

Two chimpanzees have demonstrated the ability to learn to use graphic symbols to ask one another for tools needed to obtain food. The chimps readily attended to and complied with one another's requests by selecting the appropriate tool from six distinct alternatives. They then shared the food obtained by this means and readily reversed the roles of tool requester and tool provider. Their joint accuracy was 92%, even when human experimenters were absent from the room. When they were prevented from using the graphic system (by deactivation of their keyboards), joint accuracy dropped to 10%, even though the animals could still see and hear one another and could gesture or vocalize freely. The acquisition of tool names revealed that words are at first closely and concretely linked to function, and hence that the traditional object-naming paradigm alone is a comparatively difficult starting point for the chimpanzee.This work has demonstrated that two chimpanzees have been able to comprehend the symbolic and communicative function of the symbols they use. The results raise questions concerning chimpanzee research employing other kinds of symbolic communication systems. Apparently there is little evidence, apart from anecdote or uncontrolled tests, demonstrating that either Washoe or Sarah (chimps in other investigator's projects) has fully comprehended the symbolic nature and the communicative potential of their respective gestural and graphic token symbol systems.