The effect of binocular and monocular viewing conditions on performance of rats in the Morris water maze.

The visually guided behaviour in the Morris water maze (using distal extramaze cues for navigation to a small invisible platform in a large pool of opaque water) was analyzed by comparing monocular and binocular performance of hooded rats in various versions of this task. A dish-shaped metal foil occluder connected to a carrier fixed to the frontal bones was used to restrict vision to one eye. Acquisition of the water maze task with one eye occluded proceeded at the same rate as with both eyes open. There was no difference in the transfer from binocular to monocular and from monocular to binocular viewing. Retrieval of the monocularly acquired habit was equally efficient with the same as with the contralateral eye. Similar results were obtained in naive and overtrained rats. In the working memory version of the task, rats received a single acquisition trial with a new position of the escape platform followed after a delay of 2, 5, 20 or 40 min by a single retrieval trial. Performance deteriorated with increasing delay faster under interocular transfer conditions then when the same eye was used in both trials. No signs of ocular dominance were found in this task. It is concluded that successful place learning is little affected by monocular or binocular viewing conditions, but that monocular impairment becomes apparent when the difficulty of the task is increased.