A test for order relevance in a three-element serial learning task

Rats were trained in a straight runway on a simple three-element series of differing reward quantities. The first trial of the series ended with a two-pellet reward, and the second and third trials ended with a 12-pellet reward and a nonreward, respectively (2-12-0). All animals developed accurate anticipation of the terminal nonreward in the 2-12-0 series before it was rearranged for two test days during which the elements appeared in the order 12-2-0. The rats' anticipation of the terminal nonreward did not transfer to the reordered series, a result taken to mean that anticipation had been based upon interitem associations among memorial representations of the differing reward quantities. A second transfer test to 0-0-0, given after anticipation was reestablished to the 2-12-0 series, gave evidence that the ordinal position of the series elements was also a source of anticipation; the animals continued to run relatively slowly on the third trial in extinction. In neither transfer test was there evidence that the rats employed the strategy of enumerating rewarded trials, because counting is an order-irrelevant process.