Absence of overshadowing between a landmark and geometric cues in a distinctively shaped environment: a test of Miller and Shettleworth (2007).

Rats in the first 2 experiments, which were designed to test predictions from a model of spatial learning by N. Y. Miller and S. J. Shettleworth (2007), had to escape from a triangular pool by swimming to a submerged platform in a geometrically unique corner. A spherical landmark was suspended above the platform for an overshadowing group. A control group was trained with the same arrangement and with a second, identical landmark suspended in another corner. The platform could thus be found by reference to the landmark or the geometric cues in the overshadowing group, whereas the control group had to rely on geometric cues. There was no indication of overshadowing between the geometric cues and the landmark in the overshadowing group. The final 2 experiments revealed that the absence of overshadowing was not a consequence of the landmark being an ineffective cue for overshadowing. The results indicate either that the landmark and geometric cues were not in competition for the control they acquired over behavior or that an additional process compensated for any such competition that might have occurred in the overshadowing group. This additional process could involve between-cues associations or the provision of a stable spatial framework.