Geometric vs. non-geometric information. Explaining male rats' selective preferences in a navigation task

In three experiments, male rats were trained to find a hidden platform in a Morris pool which was completely surrounded by circular curtains (black in Experiments 1 and 2, and beige in Experiment 3). Experiment 1, a preliminary experiment, addressed single landmark learning and established that a plain shiny white cylinder and a striped cylinder were of different salience. Then in Experiments 2 and 3 rats were trained in a triangular-shaped pool with the platform defined in terms of two sources of information, a landmark outside the pool (either the white or the striped cylinder) and a particular corner of the pool (as in Rodríguez, Torres, Mackintosh, & Chamizo, 2010, Experiment 2). Following acquisition, a test trial without the platform pitted these two sources of information against one another. In Experiment 2, rats spent more time in the area of the pool that corresponded to the cylinder when it was white, whereas they spent more time in the distinctive corner of the pool when the cylinder was striped. However, in Experiment 3 (with beige curtains in order to reduce the salience of the white cylinder) all rats spent more time in the distinctive corner of the pool. Subsequent tests with the two cues (landmark and pool-geometry) presented individually showed that all rats in the two experiments had learned to find the platform using the two sources of information. In addition, a clear geometry advantage was found in both groups of rats tested in Experiment 3. This study shows for the first time that changing the salience of a landmark can strongly affect the preference for a geometric cue over a landmark cue in male rats.