Communicating about distal objects: an experimental investigation of factors influencing gestural communication by chimpanzees (Pan troglodytes)
Leavens, David Alden
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A defining characteristic of intentional communication is that it is used socially; that is, an audience is required for the display of communicative behavior. A second defining feature of intentional communication is that it locates objects in time or space for an observer. Previous studies of these features of manual gesture in apes have employed very small samples (one to four subjects). The present studies explored (a) the independent effects of the arrival of an experimenter and food on gestural production in chimpanzees ( N = 35, Experiment 1), (b) the influence of food dispersion on the number of fingers extended while pointing ( N = 83, Experiment 2), and (c) the effectiveness of chimpanzees in communicating the location of hidden food ( N = 101, Experiment 3). The methods employed in these experiments differ from those used in previous studies in the following ways: (a) large samples were used, (b) only first-trial results were analyzed (i.e., every subject received each experimental condition only once), (c) “naturalistic” procedures avoided potential confounds with the effects of novel apparatus or unusual behavior on the part of the experimenters, and (d) the experiments sampled from a population of chimpanzees who had not been languagetrained or otherwise raised in intimate association with humans. The chimpanzees gestured almost exclusively during the approach or presence of a human observer (Experiment 1). Experiment 2 was inconclusive because too few chimpanzees pointed. A human observer was able to correctly guess the location of a hidden banana on 71% of 97 trials, demonstrating that chimpanzees can effectively communicate the location of hidden food without explicit training to do so.