| Research Abstract |
The present study aimed to clarify the linguistic and cognitive functions in chimpanzees both in the laboratory and in the wild, focusing on the mechanism of acquiring the skills and the social transfer among individuals especially across generations. We studied the tool use, especially stone-tool use in the wild, and also explored the following cognitive skills shown in the laboratory : Comprehension of human speech and gestural signs, acquisition of visual symbols for the artificial language, comprehension and use of number, visual information processing including the topics of biological motion, the mechanism of extracting features in visual search paradigm, establishment of natural concepts, comprehension and use of tokens, serial recognition of video images, and so forth. The laboratory works and the field works aimed to clarify the social propagation of the cognitive skills that have been acquired in each individual level. How the knowledge and skills can be transferred from one
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individual to the others? The field work in Africa focused on the tool use especially stone-tool use and the developmental process based on the longitudinal study. It proved that there was a "critical period" at the age of 3.5 to 5 years old for the acquisition of the skills. It took 9 to 10 years for the young chimpanzees to reach to the refined level of the adults. The following points may provide important basis for the social transmission of the skills from the model to the apprentice across generation ; "careful and long-term observation by the apprentice", "the strong motivation to imitate by the apprentice", "social tolerance of the model toward the apprentice", "No active teaching by the model but showing the good model behavior", etc. The laboratory works proved the following points. The study of imitation in a face to face situation revealed that the imitation of simple motor pattern without objects was difficult for the chimpanzees. This contrasted the fact that the imitation of the action involving the objects was relatively easier. The study of chimpanzee model-apprentice experiments revealed that an apprentice chimpanzee went to observe the model chimpanzee in the following two occasions, before doing the first attempt and right after his/her own failure. For the future study of the vertical transmission of the cognitive skills between the mothers and the infants, we carried out the artificial insemination to have three chimpanzees pregnant. In addition to the above described studies on chimpanzees, we did the comparative studies on orangutans, gibbons, and macaques. The results have been published in the leading journals including "Nature". Less
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