Classical conditioning is one of the most basic forms of learning in which a learned association or connection develops between two stimuli or objects. As noted by Baum et al.,¹ the eminent Russian physiologist Ivan Pavlov (1849-1936) was the first to describe the process of classical conditioning with his work on the conditioned reflex. Reflexes are specific, automatic, unlearned reactions elicited by a specific stimulus. For example, if you have ever touched a surface that you did not know was hot (such as a hot stove), you showed a reflexive behavior—the immediate withdrawal of your hand from the stove. Similarly, if a piece of dust suddenly enters your eye, your eye will automatically blink and begin to secrete tears. These unconditioned reflexes are automatic and have a great deal of survival value for the organism. Pavlov demonstrated that such unconditioned reflexes could be conditioned, or learned. While studying dogs in order to understand more fully the digestive process, he began to notice that many of the dogs secreted saliva (an unconditioned reflex to the sight or smell of food) before food was delivered to them. He observed that this phenomenon occurred whenever the dogs either heard the approaching footsteps of the laboratory assistant who fed them or had a preliminary glimpse of the food. In order to investigate this phenomenon more systematically, Pavlov developed a procedure for producing a conditioned reflex. This procedure came to be called classical conditioning. It is one of the most basic forms of learning.

Pavlov conducted a series of well-known studies on the process of classical conditioning using dogs as experimental subjects (Fig. 30.1). In these studies, Pavlov studied situations in which a neutral stimulus or event (such as a bell) was presented to a dog just prior to the presentation of food (an unconditioned stimulus that normally elicits an automatic unconditioned reflex of salivation). After a number of such presentations, the bell (now a conditioned stimulus) would elicit a conditioned or learned salivation response when presented by itself in the absence of food. The conditioned reflex of salivation occurred to the bell alone. This represents the process of classical conditioning, and it is based on the learned association or connection between two stimuli, such that the bell is associated with food, that have occurred together at approximately the same point in time. An association is learned between a weak stimulus (such as the bell) and a strong stimulus (such as the sight of food) so that the weak stimulus comes to elicit the response originally controlled only by the stronger one (i.e., salivation).

Pavlov also subsequently demonstrated what would happen if the neutral stimulus, such as a bell, was presented just prior to the presentation of an aversive stimulus such as an electric shock or a pinprick. Normally, such aversive stimuli presented alone will produce a variety of negative responses such as whining/whimpering and fear-type reactions such as urination. When the bell preceded such an aversive stimulus, eventually, the formerly neutral bell stimulus would automatically produce the negative emotional responses.

In another variety of this design, Pavlov then evaluated what would happen if, instead of preceding food with the sound of the bell, it was preceded by the aversive stimulus such as electric shock. What Pavlov found in this situation was that, after this conditioning, the dogs subsequently failed to demonstrate any negative emotional responses to the aversive stimulus. Instead, these dogs began perceiving these painful stimuli as signals that food was on the way. The electric shock now actually elicited salivation and approach behaviors.

Operant conditioning (also referred to as instrumental conditioning) is a different form of learning that was originally formulated by Edward Thorndike (1874-1949) and then more comprehensively developed by B. F. Skinner (1904-1990). Unlike classical conditioning, operant conditioning develops new behaviors that bring about positive consequences or remove negative events. In classical conditioning, a new stimulus (such as a bell) is conditioned to elicit the same responses that had previously occurred to the unconditioned stimulus, whereas in operant conditioning, a new response is learned. For example, new behaviors that produce food, social approval, or other positive consequences, or that reduce damaging or aversive events, illustrate operant behavior. The behavior “operates” on the environment to bring about changes in it. Thus, animal training, such as that involved in the learned performance of circus animals, involves basic principles of operant conditioning. Although operant training has existed for centuries, the behaviorist revolution in psychology provided the first carefully delineated methods and procedures
of operant conditioning so that such training could be accomplished most efficiently.¹ The key stimulus is reinforcement. Reinforcement refers to any consequence that increases the likelihood that a particular behavior will be repeated or that strengthens that behavior. Extinction involves the gradual decrease in the strength or tendency to perform a response due to the elimination of reinforcement. Based on these principles, what came to be known as the “Skinner box” was devised as an enclosed plexiglas box in which there was a light above a lever. The lever could be pressed down by the animal with its paws (rats were used in these early studies). Below the lever was a food tray into which food pellets could be dispensed. The task of the animal was to learn that pressing the lever (a certain number of times or at a certain rate, predetermined by the experimenter) resulted in food pellets being dispensed in the food tray. Thus, the animal learned to operate on the environment (the lever in the box) in order to receive reinforcement (food pellets).

Once the aforementioned response was learned, one could then introduce different reinforcement schedules in order to produce different patterns of responding. Reinforcement could now require variable numbers of bar presses or could be available every so often. Also, a discriminative stimulus could be introduced, so that the rat received reinforcement for pressing the bar only when the light was on in the box. The animal would soon learn not to respond when the light was off. In this manner, the rat’s bar-pressing behavior came under stimulus (e.g., light) control.

This same shaping procedure is used in training circus and other animals to perform complicated acts. Dolphins can be shaped to leap out of the water, and lions can be taught to jump through flaming hoops in order to receive some reinforcement. These techniques are used in virtually every zoo and marine animal show.

As discussed earlier, and as reviewed by Gatchel,⁶ operant conditioning refers to the strengthening of a response and behavior through reward or reinforcement. That is to say, the probability that a behavior will be performed again is increased if it is followed by some form of reinforcement. Behavior is controlled by its consequences. If a behavior is followed by a reward, it has a high probability of recurring; if it is ignored or punished, it has a low probability of recurring. Obviously, a great deal of our everyday behavior is learned and maintained through operant conditioning. For example, most of us work because of the rewards (both tangible, such as money, and intangible, such as a pleasant work environment) that it produces.

In terms of pain, many times a person in pain will elicit a great deal of sympathy and attention (both of which are rewarding). In addition, suggestions are usually made by others to rest and stay inactive, pain-relieving medications are usually administered, and often financial compensation is provided. The longer these reinforcing consequences continue, the longer the patient is likely to display the maladaptive pain behaviors such as inactivity and avoidance of work. Thus, this type of learning or conditioning can significantly contribute to the maintenance of pain behavior.

As pointed out by Baum et al.,¹ this operant conditioning conceptualization of pain was systematically employed in the operant pain treatment program originally developed at the University of Washington’s Department of Rehabilitation Medicine by Fordyce and colleagues.⁷ This program involved a 4- to 8-week inpatient period, designed to gradually increase the general activity level of the patient and to decrease medication usage. The program was based on the assumption that, although pain may initially result from some underlying organic pathologic condition, environmental reinforcement consequences (such as attention of the patient’s family and the rehabilitation staff) can modify and further maintain various aspects of “pain behavior,” such as complaining, grimacing, slow and cautious body movements, requesting pain medication, and so on. Viewing pain as an operantly conditioned behavior, Fordyce and colleagues⁷ assumed that the potentially reinforcing consequences, such as the concern and attention from others, rest, medication, and avoiding unpleasant responsibilities and duties, as well as other events, frequently follow and reinforce the maladaptive pain behavior and, as a consequence, hinder the patient’s progress in treatment.

In their treatment program, Fordyce and colleagues⁷ systematically controlled environmental events (e.g., attention, rest, medication) and made them occur contingent on adaptive behaviors. A major goal of the program was to increase positive behaviors, such as participation in therapy and activity level, while simultaneously decreasing or eliminating negative pain behaviors. It should also be noted that members of the patient’s family were actively involved in the treatment program and worked closely with the rehabilitation staff. They were taught how to react to the patient’s behavior in a manner that would reduce pain and to maximize the patient’s compliance with, and performance in, the rehabilitation program. Using this operant approach, the patient was basically taught to reinterpret the sensation of pain and tolerate it while performing more adaptive behaviors that would gain the attention and approval of others. Such a program was initially conducted in the hospital and would later be continued on an outpatient basis. These programs proved to be very successful
at decreasing pain behaviors while increasing the levels of activities of daily living.