Rat's numerical ability explored: Identification of ordinal numbers (3rd-12th)

Tessei Kobayashi and Kotaro Suzuki

University of Tokyo, Japan

Using Davis and Bradford's (1986) task, we explored the numerical ability of rats (Rattus norvegicus). The task was to enter one box of defined ordinal number among an array of boxes in a large enclosure. The position of boxes was varied from trial to trial. There were a total of 8 experiments. In Experiments 1 and 2, all of 3 rats correctly chose the 4th box from arrays of 6 and 12 boxes, respectively. In Experiments 3, where the ordinal number of the correct box was increased in a graduated fashion (N+1), 2 rats were able to select the correct box even when its position was higher than 10th among 12. In Experiment 4, they were successful also in an arrangement of 18 boxes. In Experiment 5, a possibility that rats had used cues to the openability of box doors was ruled out. In Experiments 6, in which 4 new rats were introduced as subjects, the 3rd box was correct, and the total number of the boxes was varied from trial to trial. Three rats succeeded in the task, indicating that performance was not based on the relative position of boxes. In Experiment 7, the ordinal number of the correct box was increased in a stepwise fashion (as in Experiment 3) while the total number of boxes was simultaneously varied. Two rats succeeded even when the correct box was in position 7. In Experiment 8, both small- and large-sized boxes were used to control for the possibility of using the cumulative length of the boxes as a cue. Overall, the results suggest that performance was based on numerical cues. Intentional acts were occasionally observed but appeared not to be essential for solving the task.

Davis, H., & Bradford, S. A. (1986). Counting behavior by rats in a simulated natural environment. Ethology, 73, 265-280.

Suzuki, K., & Kobayashi, T. (in press). Numerical competence in rats (Rattus norvegicus): Davis & Bradford (1986) extended. Journal of Comparative Psychology, 114.

Kobayashi, Tessei

Department of Cognitive & Behavioural Science, University of Tokyo

3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan

tessei@darwin.c.u-tokyo.ac.jp