Reduced visual acuity impairs place but not cued learning in the Morris water task

The Morris water task is a standard method for testing spatial learning in rodents. In a place version of the task, animals utilize multiple visual cues to learn the location of a hidden platform. The ability of animals to locate a cued platform is often used to qualitatively test for possible non-cognitive contributions to deficient place learning, including reduced visual function. We investigated the role of visual acuity in water maze performance quantitatively by depriving rats of pattern vision during a critical period for visual plasticity, which reduced their acuity by approximately 27% and then tested them in typical place and cued platform configurations of the Morris water task. Animals with reduced visual acuity had a significant deficit in place learning, but eventually reached the same escape latency as non-deprived animals. Deprived and non-deprived animals, however, did not differ in their ability to locate a cued platform following place learning. These data indicate that reduced visual acuity in rats can influence measurement of their place learning and that a typical cued platform version of the task cannot detect a modest, but significant, visual deficit.