The effect of negative stimulus presentations on observing-response rates

Theories of observing differ in predicting whether or not a signal for absence of reinforcement (S-) is capable of reinforcing observing responses. Experiments in which S- was first removed from and then restored to the procedure have yielded mixed results. The present experiments suggest that failure to control for the direct effect of presenting S- may have been responsible. Pigeons and operant procedures were used. Experiment 1 showed that presentations of S-, even when not contingent on observing, can raise the rate of an observing response that was reinforced only by presentations of a signal (S+) that accompanied a schedule of food delivery. Experiment 2 showed that this effect resulted from bursts of responding that followed offsets of S-. Experiment 3 showed that, when the presence of S- was held constant, lower rates occurred when S- was dependent on, rather than independent of, observing. These results support theories that characterize S- as incapable of reinforcing observing responses.