Authors: Misato Hayashi Tetsuro Matsuzawa
Publish Date: 2003/08/07
Volume: 6, Issue: 4, Pages: 225-233
Abstract
This study focuses on the development of spontaneous object manipulation in three infant chimpanzees during their first 2 years of life The three infants were raised by their biological mothers who lived among a group of chimpanzees A human tester conducted a series of cognitive tests in a triadic situation where mothers collaborated with the researcher during the testing of the infants Four tasks were presented taken from normative studies of cognitive development of Japanese infants inserting objects into corresponding holes in a box seriating nesting cups inserting variously shaped objects into corresponding holes in a template and stacking up wooden blocks The mothers had already acquired skills to perform these manipulation tasks The infants were free to observe the mothers manipulative behavior from immediately after birth We focused on object–object combinations that were made spontaneously by the infant chimpanzees without providing food reinforcement for any specific behavior that the infants performed The three main findings can be summarized as follows First there was precocious appearance of object–object combination in infant chimpanzees the age of onset 8–11 months was comparable to that in humans around 10 months oldSecond object–object combinations in chimpanzees remained at a low frequency between 11 and 16 months then increased dramatically at the age of approximately 15 years At the same time the accuracy of these object–object combinations also increased Third chimpanzee infants showed inserting behavior frequently and from an early age but they did not exhibit stacking behavior during their first 2 years of life in clear contrast to human dataThis study was supported by grants from the Ministry of Education Science and Culture in Japan to the second author 12002009 10CE2005 and 21COE program A2 to Kyoto University We would like to thank Masaki Tomonaga Masayuki Tanaka Hideko Takeshita Masuo Koyasu and Sakiko Yoshikawa for helpful support and suggestions Special thanks are due to Masako MyowaYamakoshi and Yu Mizuno for their advice and help given during the course of conducting experiments We also thank Dora Biro for help given in the course of revising the manuscript We are grateful to all of the staff at the Primate Research Institute of Kyoto University who work with the chimpanzees The present study complies with the laws of Japan
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