Chimpanzee (Pan troglodytes) pointing: hand shapes, accuracy, and the role of eye gaze.

The manual pointing of 2 signing chimpanzees, Moja and Tatu, was examined in 2 experiments. Experiment 1 investigated eye-gaze direction, hand use, and hand shape while pointing. Both chimpanzees obtained the attention of a human before pointing toward an unreachable object. During 100 trials, the chimpanzees alternated their eye gaze between the object and the human while pointing. Moja's points were left-hand biased, and Tatu showed no lateral hand bias. Both indexical and whole hand points were recorded. Experiment 2 tested the chimpanzees' ability to point accurately toward objects in close proximity to each other. Humans were able to reliably determine the locations toward which the chimpanzees pointed. Both chimpanzees showed left-hand biases, and a higher proportion of indexical points were observed than in Experiment 1. These results are compared and contrasted with recent hypotheses pertaining to the topography of chimpanzee pointing and the role of eye gaze in deictic interactions.