Compound stimulus control of operant, but not adjunctive, behavior

Compound stimulus control of operant (barpress) and adjunctive (polydipsia) behaviors was investigated by training rats under a multiple schedule of food delivery. Four rats (operant group) were reinforced for barpressing during light (L+T) or tone (U+T). For half of the operant group, barpressing was not reinforced during no light and no tone (L+T), while the other half were not reinforced during light and tone (L+T). The four adjunctive behavior rats were each yoked to a rat in the operant group so that food pellets were delivered to the yoked rats at the same rate and during the same stimulus conditions. The adjunctive behavior recorded was the licking of a water bottle induced by the intermittent delivery of food. When a compound stimulus was presented that was composed exclusively of the light and tone elements that had been paired with food-pellet delivery and increased barpressing or licking, it controlled the highest response rate of all stimuli (additive summation) for the operant behavior but not for the adjunctive behavior.