a device used to test spatial learning in nonhuman animals, consisting of a water-filled tank with a platform hidden underwater. An animal is placed in the water and can escape only by finding and climbing on the hidden platform. Typically, a variety of external cues are provided for spatial reference. The Morris water maze is often used to evaluate the effects of brain lesions or drug manipulations on spatial learning and memory. [devised in 1981 by Richard G. M. Morris, British neuroscientist]