Scores of experiments in the field of animal learning have demonstrated that conditioning to a stimulus depends not merely on its current relationship with a reinforcer, but is affected by animal's past experience with that stimulus. Latent inhibition (LI) is one case of such a biasing effect of past experience: it reflects the proactive interference of nonreinforced stimulus preexposure on the subsequent performance of a learning task involving this stimulus (Lubow,1973, 1989; Lubow, Weiner, & Schnur, 1981).

LI can be demonstrated in a variety of classical and instrumental conditioning procedures, and in many mammalian species, including humans (Lubow, 1973, 1989; Lubow et al., 1981). While a variety of behavioral tasks are used to demonstrate LI in rodents, all of them share a basic procedure. In the first stage, preexposure, animals from each of two groups are placed in an environment that will later serve as the conditioning–test apparatus. Subjects in the “stimulus preexposed” (PE) group are repeatedly exposed to a stimulus (e.g., tone) which is not followed by a significant consequence. Subjects in the “nonpreexposed” (NPE) group spend an equivalent amount of time in the apparatus without receiving the stimulus. When the preexposure stage is completed, either immediately, or a certain time later, all of the subjects enter the conditioning stage, in which the preexposed stimulus is paired with a reinforcer over a number of trials. Performance is assessed by examining some behavioral index of conditioned responding, either during the conditioning stage or in a third, test stage.