[Response occurrence to the non-reinforced alternative through punishment in rats]

Each of eight rats was located in the experimental chamber mounted with two levers. Lever-pressing to either of the two was maintained by a schedule of food. After that, a punishment schedule of electric shocks was added. Neither the reinforcement nor the punishment schedule was programmed on the other lever, i.e. the non-reinforced alternative. The effect of reinforcement, and the joint effect of reinforcement and punishment on responses to the non-reinforced alternative were compared. During punishment sessions, responses to the non-reinforced alternative occurred significantly more often than during reinforcement sessions. The number of responses to the non-reinforced alternative was negatively correlated with that to the reinforced alternative during punishment sessions. Nevertheless, the occurrence of responses to the non-reinforced alternative was mainly observed during the first few sessions in punishment schedule, or after stepping up the intensity of electric shock. These results were discussed in relation to the two theories and models of punishment. The results imply that the two theories and models of punishment are necessary to explain the effect of punishment.