Navigation with two landmarks relatively far from a goal in rats (Rattus norvegicus): The role of landmark salience

Male and female rats were extensively trained in a Morris pool to find a hidden platform in the presence of a configuration formed by 2 landmarks and the effects of varying the salience of one of the landmarks were studied. The two landmarks could be either of different salience (i.e., B and c, Group Bc) or of the same salience (i.e., b and c, Group bc) and they were relatively far (110 cm) and equidistant from the hidden platform. Rats in Group Bc ended up being faster to reach the platform than rats in Group bc, and males were always faster to find the platform than females. No sex differences were found on subsequent test trials without the platform (i.e., when a different measure was used). The results showed a clear salience effect: The best rats’ performance was when the more salient landmark, B, was present, either by itself or in compound with landmark c. A final test trial, a conflict test, was also conducted with the two landmarks in compound although reversing their relative positions, in order to test the preference for the geometry they formed, a straight line (independently of the landmarks’ identities), vs. the landmarks identities, B or b. All rats showed a preference for the geometry formed by the two landmarks, independently of their identities.