ABSTRACT
In the everyday world, human behavior is changed by signs, symbols, gestures, and spoken words. Sounds, smells, sights, and other sensory stimuli that do not depend on social conditioning also regulate behavior. When social or nonsocial events precede operant behavior and affect its occurrence, they are called controlling stimuli. A controlling stimulus (S) is said to alter the probability of an operant, in the sense that the response is more (or less) likely to occur when the stimulus is present. 1
One kind of controlling stimulus that we discussed in Chapter 4 is the S D or discriminative stimulus . An S D is a controlling stimulus that sets the occasion for reinforcement of an operant. In a pigeon experiment, a red light may reliably signal the presentation of food for pecking a key. After some experience, the bird will immediately strike the key when it is illuminated with the red light. Thus, the discriminative stimulus sets the occasion for a high probability of response.
