Stimulus exposure and discrimination in rats: A test of a theory for the role of contextual factors

In two experiments rats were trained on a simultaneous discrimination in a jumping stand. On each trial choice always lay between one stimulus (an obliquely striped object in Experiment I, and a plain grey object in Experiment II) and a second that varied from trial to trial. On half the trials this variable stimulus bore horizontal stripes (H) and on the remaining trials it bore vertical stripes (V). It was argued that the solution of this discrimination would be hindered if the animals tended to classify H and V apart (Bateson and Chantrey, 1972). It was found, however, that prior exposure to H and V in the home cage (which has been supposed to promote classifying apart) facilitated learning and that prior exposure to H and V in the apparatus itself (which might be thought to promote classifying together) hindered later learning. Possible alternative accounts for these exposure learning effects are discussed.