Stimulus Increasing the Probability of a Behavior
stimulus control is the phenomenon of a stimulus increasing the probability of a behavior (operant response) because of a history of that behavior being differentially reinforced in the presence of the stimulus. In other words, stimulus control is basically learning to pay attention to things that we identify in the environment (discriminative stimuli) that give us information about the effectiveness of our behavior: what behavior is likely to be effective or ineffective, under which conditions, and what the behavior gives us (reinforcement or punishment). Therefore, in the presence of those stimuli we are likely to respond differentially. Imagine the following experiment. A pigeon is trained to peck an unlit left key in order to obtain food (reinforcer). After the animal learns this simple task, a right key is lit. Because the right key gives little information to the pigeon, after some time it is ignored. But what would happen if we changed the procedure, turning the light on and off, and giving food to the pigeon only when it pecks the left key when the right key is lit? Under these conditions, the pigeon starts to peck the left key when the right key is lit, and not when it is dark. Thus, we can say that the pigeon starts to respond differently in the presence of these two stimuli (right key lit or dark). That is, the discriminative stimulus is controlling the pigeon’s behavior. In this context, control does not mean that the pigeon has no choice; it only refers to the probability of responding in the presence of the discriminative stimulus (lit right key).