Abstract numerical discrimination learning in rats

Rhesus Monkeys Have a Counting Ability and Can Count from One to Six

Counting ability is one of the many aspects of animal cognition and has enjoyed great interest over the last couple of decades. The impetus for studying counting ability in nonhuman animals has likely come from more than a general interest in animal cognition, as the analysis of animal abilities amplifies our understanding of human cognition. In addition, a model animal with the ability to count could be used to replace human subjects in related studies. Here we designed a behavioral paradigm to train rhesus monkeys to count 1-to-6 visual patterns presented sequentially with long and irregular interpattern intervals on a touch screen. The monkeys were required to make a response to the sixth pattern exclusively, inhibiting response to any patterns appearing at other ordinal positions. All stimulus patterns were of the same size, color, location, and shape to prevent monkeys making the right choice due to non-number physical cues. In the long delay period, the monkey had to enumerate how many patterns had been presented sequentially and had to remember in which ordinal position the current pattern was located. Otherwise, it was impossible for them to know which pattern was the target one. The results show that all three monkeys learned to correctly choose the sixth pattern within 3 months. This study provides convincing behavioral evidence that rhesus monkeys may have the capacity to count.

Precise relative-quantity judgement in the striped field mouse Apodemus agrarius Pallas

Applying the classical experimental scheme of training animals with food rewards to discriminate between quantities of visual stimuli, we demonstrated that not only can striped field mice Apodemus agrarius discriminate between clearly distinctive quantities such as 5 and 10, but some of these mice also exhibit high accuracy in discriminating between quantities that differ only by one. The latter include both small (such as 2 versus 3) and relatively large (such as 5 versus 6, and 8 versus 9) quantities of elements. This is the first evidence of precise relative-quantity judgement in wild rodents. We found striking individual variation in cognitive performance among striped field mice, which possibly reflects individual cognitive variation in natural populations. We speculate that high accuracy in differentiating large quantities is based on the adaptive ability of wild rodents to capture subtle changes in their environment. We suggest that the striped field mouse may be a powerful model species to develop advanced cognitive tests for comparative studies of numerical competence in animals and for understanding evolutionary roots of quantity processing.

Concurrent learning of multiple oddity discrimination in rats

This experimental series examines rats' concurrent learning of multiple oddity discrimination and its transfer to novel stimuli. Three rats were trained to discriminate an odd object from five identical objects in a row. After acquisition of the AAAAAB problem, the BBBBBA set was added to training. At the start of concurrent training with both sets, performance on BBBBBA was significantly below chance, suggesting that rats had acquired a tendency to respond to and/or avoid specific features of objects during the initial AAAAAB training. Although all rats learned the two problems reliably, no transfer effect was observed during tests with novel sets CCCCCD and DDDDDC. After the first transfer test, rats performed reliably for stimulus sets AAAAAB, BBBBBA, CCCCCD, and DDDDDC concurrently. Although one rat showed reliable transfer for novel test problems EEEEEF and FFFFFE, the possibility of biased test performance between stimulus sets, by choosing one of two test objects, could not be excluded. However, following the transfer tests, all rats responded significantly to 20 novel problems immediately after they were introduced into training. These findings offer evidence of rats' capacity for concurrent oddity discrimination using multiple stimulus sets, as well as preliminary evidence of relational oddity learning in rats.