Learning the rules of the rock–paper–scissors game: chimpanzees versus children
The present study aimed to investigate whether chimpanzees (Pan troglodytes) could learn a transverse pattern by being trained in the rules of the rock–paper–scissors game in which “paper” beats “rock,” “rock” beats “scissors,” and “scissors” beats “paper.” Additionally, this study compared the learning processes between chimpanzees and children. Seven chimpanzees were tested using a computer-controlled task. They were trained to choose the stronger of two options according to the game rules. The chimpanzees first engaged in the paper–rock sessions until they reached the learning criterion. Subsequently, they engaged in the rock–scissors and scissors–paper sessions, before progressing to sessions with all three pairs mixed. Five of the seven chimpanzees completed training after a mean of 307 sessions, which indicates that they learned the circular pattern. The chimpanzees required more scissors–paper sessions (14.29 ± 6.89), the third learnt pair, than paper–rock (1.71 ± 0.18) and rock–scissors (3.14 ± 0.70) sessions, suggesting they had difficulty finalizing the circularity. The chimpanzees then received generalization tests using new stimuli, which they learned quickly. A similar procedure was performed with children (35–71 months, n = 38) who needed the same number of trials for all three pairs during single-paired sessions. Their accuracy during the mixed-pair sessions improved with age and was better than chance from 50 months of age, which indicates that the ability to solve the transverse patterning problem might develop at around 4 years of age. The present findings show that chimpanzees were able to learn the task but had difficulties with circularity, whereas children learned the task more easily and developed the relevant ability at approximately 4 years of age. Furthermore, the chimpanzees’ performance during the mixed-pair sessions was similar to that of 4-year-old children during the corresponding stage of training.
KeywordsRule learning Comparative cognition Transverse pattern Circular relationships Non-linear relationships
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT)/Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant 16H06283 to T. M., and grant 15H05709 to M. T.); the MEXT National BioResource Project GAIN, the JSPS core-to-core CCSN and the JSPS-LGP-U04 to T. M. The authors would also like to thank the Xinfei Kindergarten in Xinxiang, Henan, China for their facilitation of the experiment with the children, and the staff of KUPRI for taking care of the chimpanzees. Our thanks are also due to Ikuma Adachi, Misato Hayashi, Fumito Kawakami, Etsuko Ichino, Akiho Muramatsu, Duncan Wilson, Yoshiki Kurosawa, Gabriela Melo Daly, Tomoko Takashima, and Akemi Hirakuri of KUPRI for their help with this study. We also thank Mr. Xia for the technical help with the early version of the program.
Compliance with ethical standards
J. G., Y. S., M. T., and T. M. designed the experiment; J. G., T. M., and M. T. collected the chimpanzee data; J. G. collected the child data; and J. G., Y. S., M. T., and T. M. wrote the manuscript.
Conflict of interest
The authors declare that they have no conflicts of interest.
The research proposal for the chimpanzees was approved by the Animal Welfare and Animal Care Committee of KUPRI and by the Animal Research Committee of Kyoto University (Nos. 2015-044, 2016-064). All procedures adhered to the Japanese Act on the Welfare and Management of Animals. The research proposal for the experiment with children was approved by the Human Research Ethics Committee of KUPRI (No. 2016-011).
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