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.