Formation of number concept in a chimpanzee

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To teach a female chimpanzee the concept of cardinal and ordinal number, the following 4 experiments were carried.In Experiment 1, she was trained to match an Arabic numerals as the cardinal number to the number of dots displayed in a random pattern. Starting with one and two, the next large number was added, one by one, when the criterion of learning was attained. Sixteen, 18, 24, 45, and 55 sessions were required to the criterion in each stage from the number 2 to 6, respectively.In Experiment 2 and 3 in which the number 7 was added, the pattern and density of dots were varied systematically to check those effects as the discriminative stimuli upon matching behavior. Although some disturbance was observed, her performance was still maintained higher than 85% correct. Response time consistently increased as a function of the numbers of dots except that the largest number 7 was reponded faster than 6. Thus, the chimpanzee's matching behavior should be controlled by the number of dots.As the first step to teach the ordinal numbers, the large-small conditional discrimation was trained in Experiment 4 with 6 adjacent pairs in 1 to 7 numeral series. After reaching the criterion, non-adjacent pairs were inserted as probe trials to test the transitivity. The chimpanzee was successful to show the forward transitivity to the larger number, but not the backward transitivity to the smaller number.