The Floor Projection Maze: A novel behavioral apparatus for presenting visual stimuli to rats.

There is a long tradition of studying visual learning in rats by presenting stimuli vertically on cards or monitors. The procedures are often labor intensive and the rate of acquisition can be prohibitively low. Available evidence suggests that rats process visual information presented in the lower visual hemifield more effectively than information presented in the upper visual hemifield. We capitalized on these findings by developing a novel apparatus, the Floor Projection Maze, for presenting visual information directly to the floor of an exploratory maze. Two-dimensional (2D) visual stimuli were presented on the floor by back-projecting an image from a standard digital projector to the semi-transparent underside of the floor of an open maze. Long-Evans rats rapidly acquired easy 2D visual discriminations (Experiment 1). Rats were also able to learn a more difficult shape discrimination in dramatically fewer trials than previously reported for the same discrimination when presented vertically (Experiment 2). The two choice discrimination task was adapted to determine contrast sensitivity thresholds in a naïve group of rats (Experiment 3). Contrast sensitivity thresholds were uniform across three subjects, demonstrating that the Floor Projection Maze can be used for visual psychophysics in rats. Our findings demonstrate that rats can rapidly acquire visual tasks when stimuli are presented horizontally on the floor, suggesting that this novel behavioral apparatus will provide a powerful behavioral paradigm in the future.