The influence of passive preexposure on escape from a Morris pool

In 3 experiments rats were preexposed to the landmarks that surround a Morris pool by being placed on a submerged platform within the pool. They were then required to escape from the pool by swimming to the platform, which was in a location that had not been used during preexposure. Preexposure facilitated subsequent escape from the pool, provided that the platform was not moved during preexposure and the relative position of the landmarks to each other remained constant throughout preexposure. In contrast, if during preexposure the platform was moved from session to session (Experiment 1), or the array of landmarks was altered unsystematically from trial to trial (Experiments 2 and 3), then subsequent learning to escape from the pool was disrupted. These findings suggest that the effects of preexposure to the landmarks in a Morris pool is determined by whether or not they are of relevance for identifying the location of the platform. When they are relevant, then subsequent learning is facilitated, but when they are irrelevant, then subsequent learning is disrupted.