Overshadowing of geometry learning by discrete landmarks in the water maze: effects of relative salience and relative validity of competing cues.

The effects of stimulus salience and cue validity in the overshadowing of geometric features of an enclosed arena by discrete landmarks were investigated in rats using the water maze paradigm. Experiment 1 established that in a rhomboid-shaped arena, the acute corner was more salient than the obtuse corner. In Experiment 2, rats were trained to find a submerged platform either in one of the acute, or obtuse, corners. In addition to the information provided by corner angle, the platform was also signaled by the presence of a spherical landmark suspended above the platform for rats in the experimental group. The landmark was a more valid cue for predicting the location of the platform than the angle of the corner. This training resulted in overshadowing of learning about the angle of the corner by the presence of the landmark. The final experiment extended this result by showing that when the predictive validities of the angle and the landmark were matched in the experimental group, learning about geometry was still overshadowed by the presence of landmarks, but only in animals that were trained with the platform at an obtuse, but not acute, corner. These results uniquely demonstrate that learning about geometry can be overshadowed by discrete landmarks, and also that whether overshadowing is observed depends on the stimulus salience and the relative validity of the competing cues. These findings imply that learning based on geometric cues follows the same basic rules that apply to a wide range of other learning paradigms.