Producing either positive or negative tendencies to a stimulus associated with shock.

A technique is described in which rats are pretrained with reinforcement to bar press. Each bar press was associated with a tone. This tone was later paired with one of two aspects of an electric shock, either at the onset or at the end of the shock, in a situation in which the shock is inescapable. These animals were retested in the operant situation under conditions of extinction, but with tone present as a conditioned reinforcer. The finding was that animals for which the tone was associated with shock onset extinguished quickly, whereas animals for which the tone was paired with shock termination extinguished more slowly.