COMPREHENSION OF CAUSE-EFFECT RELATIONS IN A TOOL-USING TASK BY CHIMPANZEES (PAN-TROGLODYTES)

Five chimpanzees (Pan troglodytes) were tested to assess their underst anding of causality in a tool task. The task consisted of a transparen t tube with a trap-hole drilled in its middle. A reward was randomly p laced on either side of the hole. Depending on which side the chimpanz ee inserted the stick into, the candy was either pushed out of the tub e or into the trap. In Experiment 1, the success rate of 2 chimpanzees rose highly above chance, but that of the other subjects did not. Res ults show that the 2 successful chimpanzees selected the correct side for insertion beforehand. Experiment 2 ruled out the possibility that their success was due to a distance-based associative rule, and the re sults favor an alternative hypothesis that relates success to an under standing of the causal relation between the tool-using action and its outcome.