Compound stimulus control by discriminative stimuli associated with high and moderate response rates

Four rats received water on a fixed-ratio schedule for lever pressing in the presence of a tone (or light) stimulus and on a variable-interval schedule in the presence of a light (or tone) stimulus. Following stabilization of a high response rate during the fixed-ratio component and a moderate response rate during the variable-interval component, brief periods with the light and tone presented simultaneously but with no responses reinforced were inserted into the regular training schedule. Response rates during the compound stimuli were intermediate between the response rates controlled by the individual fixed-ratio and variable-interval associated stimuli.