Relative quantity judgment by Asian elephants (Elephas maximus)
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This study investigated whether Asian elephants can make relative quantity judgment (RQJ), a dichotomous judgment of unequal quantities ordered in magnitude. In Experiment 1, elephants were simultaneously shown two baskets with differing quantities of bait (up to 6 items). In Experiment 2, elephants were sequentially presented with baits, which could not be seen by elephants in their total quantities. The task of elephants was to choose the larger quantity in both experiments. Results showed that the elephants chose the larger quantity with significantly greater frequency. Interestingly, the elephants did not exhibit disparity or magnitude effects, in which performance declines with a smaller difference between quantities in a two-choice task, or the total quantity increases, respectively. These findings appear to be inconsistent with the previous reports of RQJ in other animals, suggesting that elephants may be using a different mechanism to compare and represent quantities than previously suggested for other species.
KeywordsNumerical cognition Relative quantity judgment Elephants
We wish to thank the directors and keepers at Ueno Zoological Garden and Ichihara Elephant Kingdom, and their elephants for their participation in the study. We also like to thank Dr. Takafumi Ishida for his editorial support. These experiments comply with the current laws of Japan and the animals are kept at the standards established by Japanese Association of Zoos and Aquariums.
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