Modification of a stimulus-reinforcer interaction by blocking

With tone-light compound-stimulus training, light will gain control of responding under an appetitive schedule while tone will gain considerable control with avoidance training. The present experiment sought to determine whether this stimulus-reinforcer interaction could be modified by a "blocking" procedure. Initially, one group of rats was trained to respond for food in tone while tone-off was food free, and a second group was trained to avoid shock in light while light-out was shock free. Following attainment of a 10:1 discrimination ratio, food and avoidance schedules were signaled, for the respective groups, by a tone-light compound stimulus. An element test demonstrated that the blocking procedure overcame the stimulus-reinforcer interaction previously reported with rats in both the appetitive and avoidance groups. Contrary to previous stimulus-reinforcer interaction research, here, the tone, rather than the light, controlled responding after food training while the light, rather than the tone, controlled responding after avoidance training. These results obey predictions from associative theory. The current experiment is also the first demonstration of blocking within an instrumental avoidance procedure.