Free-operant compounding of variable-interval and low-rate discriminative stimuli

Four rats were trained on a schedule containing stimuli associated with variable-interval 30-sec and differential-reinforcement-of-low-rate 20-sec schedules of reinforcement. Subsequently, a stimulus compounding test was administered that included individual presentations of two intensities of each stimulus plus compounds of these stimuli. In training, extremely high rates were emitted to the variable-interval stimulus, and very low rates to the differential-reinforcement-of-low-rate stimulus. Compounding the two training stimuli always produced an overall response rate intermediate between the rates controlled by the two stimuli separately presented. Essentially the same relationship held with different stimulus intensities. These results resolve the confounding of response and reinforcement variables present in previous conditioning studies reporting response averaging. They are discussed in terms of the incompatibility of the response chains associated with the individual stimuli compounded.