Discriminative Stimuli and Motivative Operations

At this point it is also important to discuss the distinction between a discriminative stimulus (SD) and a motivative operation. The MO affects the value of reinforcers where as SDs are antecedent stimuli that are correlated with the availability of reinforcement. For instance, in the case of a CMO-R, the presentation of an instructional task by the teacher does not make its removal available (the student may not be able to escape from a particular task); however, it does make removal of the task more valuable and will evoke behaviors that have been effective in the past in avoiding the task. For a transitive MO, such as the case where a bowl of cereal is presented without a spoon, the increased value of the spoon does not make that spoon more available. Needing a spoon is different from being able to obtain a spoon. Wanting a spoon does not mean there will be any spoons available. Likewise, being hungry doesn’t mean food is available; being cold does not mean that a heater is nearby. However, in the case of hunger, a restaurant sign might be an SD for food availability; sight of a coat might be an Sd for putting it on.