Abstract
These experiments seek to compare the operant rates to single stimulus inputs in 2 modalities, with the rates to compound presentations of these stimuli. In each experiment 4 rats were intensively trained on a multiple schedule. In Experiment I an intensity generalization test was administered along both modalities prior to a summation test. The summation test included individual presentations of 2 intensities from each modality plus compounds of these stimuli. In Experiment II the summation test was administered without a prior generalization test. In 29 out of 32 compound presentations a greater number of responses was emitted to a compound stimulus than to either element presented individually.