Unique numerical competence of Asian elephants on the relative numerosity judgment task

Many animals demonstrate numerical competence even without language. However, their representation is mainly based on inaccurate quantity instead of absolute numbers. Thus, their performance on numerical tasks is affected by the distance, magnitude, and the ratio of comparisons (i.e., as distance decreases, magnitudes increase, or as ratios increase the accuracy of discrimination decreases). We report that Asian elephants' numerical representation is quite different from that of other animals. We trained three Asian elephants to use a touch-panel apparatus and one female successfully learned to use the apparatus. Next, a relative numerosity judgment task was presented on the screen and the elephant was asked to touch, with the tip of her trunk, the figures with the larger numbers of items. The numbers of items in each figure ranged from 0 to 10. We found that her performance was unaffected by distance, magnitude, or the ratios of the presented numerosities but, consistent with observations of human counting, she required a longer time to respond to comparisons with smaller distances. This study provides the first experimental evidence that nonhuman animals have cognitive characteristics partially identical to human counting.