Conditional reinforcers and informative stimuli in a constant environment.

Five pigeons responded on steady-state concurrent variable-interval variable-interval schedules of food presentation in which half of the foods were removed and replaced with nonfood stimuli. Across conditions, the stimuli were either paired or unpaired with food, and the correlation between the ratio of food deliveries on the two alternatives and the ratio of nonfood stimuli was either -1, 0, or +1. Neither the pairing of stimuli with food, nor the correlation between stimuli and food, affected generalized-matching performance, but paired stimuli had a demonstrable effect at a local level of analysis. This effect was independent of the food-stimulus correlation. These results differ from results previously obtained in a frequently changing environment. We attribute this difference in results to differences in the information value of response-contingent stimuli in frequently changing versus relatively constant environments, as well as to differences between forward pairing and simultaneous pairing of the stimuli with food.