Inhibitory Stimulus Control Under Conditions of Signalled and Unsignalled Delay of Reinforcement

Abstract

In Experiment 1, pigeons received delayed reinforcement during one component of a multiple variable-interval (VI) 1-min. variable-interval 1-min. schedule of food reinforcement. One unsignalled and four signalled delay schedules were examined, but in all cases a plain white key was associated with the immediate reinforcement schedule, and a black vertical line on a white background was associated with the delayed reinforcement schedule. The incremental generalization gradients that were obtained along the line-orientation dimension suggested that the stimulus associated with each delayed reinforcement schedule was exerting inhibitory control. The unsignalled delay schedule, however, generally maintained lower rates of responding than the signalled delay schedules. In addition, unsignalled delay did not produce behavioral contrast. In Experiment 2, pigeons were trained on a multiple schedule containing VI 1-min. schedules with signalled and unsignalled reinforcement delay. All subjects responded more slowly during the unsignalled than the signalled delay schedule, and the incremental generalization gradients that were obtained suggested that the stimulus associated with an unsignalled delayed reinforcement schedule was exerting inhibitory control.