Mice were placed into one side of four identical two-compartment boxes that were constructed of acrylic (40 × 40 cm total area) and consisted of one black-walled side with a white floor and a white-walled side with a black floor, both separated by a vertically sliding door. Initial placement into the black or white compartments was counterbalanced within all genotypes. After a 15-min exposure to one of the compartments, the door was opened, and the time spent and activity (beam breaks) in the novel and familiar sides were measured during a 20-min preference test by infrared beam disruptions. Chance performance in this apparatus is indicated by a time of 600 sec spent in the novel compartment.
