Rats spontaneously discriminate purely visual, two-dimensional stimuli in tests of recognition memory and perceptual oddity.

Animal models have been central to advances made in understanding the neural basis of human cognition, but maximizing the use of animal models requires tasks that match those used to assess human subjects. Tasks used in humans frequently use visual 2-dimensional stimuli, assess 1-trial learning, and require little pretraining. This article describes novel versions of 2 tasks for the rat, spontaneous object recognition and spontaneous oddity preference, both of which use purely visual, 2-dimensional picture-card stimuli, test 1-trial learning, and require no pretraining. Rats showed robust memory for a variety of picture-card stimuli, demonstrating almost no loss of memory for some of the stimulus types even after a 2-hr delay period. Rats were able to show spontaneous oddity preference for all 3 visual stimulus types tested (photos, shapes, and patterns), as well as for 3-dimensional objects. These 2 tasks are quick to administer, involve no fearful learning associations, and require a simple apparatus. They may be particularly useful for high-throughput pharmacological or genetic screening using rodent models.