Compounding olfactory and auditory discriminative stimuli on a free-operant baseline

The simultaneous presentations of independently-established discriminative stimuli can control rates of operant responding higher than rates maintained by the individual stimuli. This "additive-summation" phenomenon has been shown with a variety of different reinforcers (e.g. food, water, and cocaine). Discriminative stimuli previously used in such studies have been limited to visual and auditory sensory modalities. The present experiment sought to (1) establish free-operant stimulus control with an olfactory discriminative stimulus, (2) compare this control to that produced with an auditory discriminative stimulus, and (3) determine whether compounding independently-established olfactory and auditory discriminative stimuli can produce additive-summation. Rats barpressed for food on a variable-interval schedule in the presence of either a tone or an odor. In the absence of these stimuli responding was not reinforced. During stimulus compounding tests, the tone-plus-odor compound occasioned more than double the responses occasioned by either the tone or odor presented individually (additive-summation).