Summation of conditioned suppression.

Four rats were trained to suppress responses in the presence of two separately presented stimuli that signalled shock in a conditioned-suppression paradigm. The two stimuli that signalled shock were then presented simultaneously to evaluate the effect of stimulus compounding on conditioned suppression. Two rats were tested by presenting the compound conditioned stimulus while conditioned suppression was being maintained to the individual conditioned stimuli. The other two rats were tested by giving them random presentations of the compound conditioned stimulus and the single conditioned stimuli during extinction of conditioned suppression. All four rats showed greater suppression to the compound stimulus than to either stimulus presented alone.