Enduring Issues in Learning

Learning5

Enduring Issues in Learning

Classical Conditioning • Elements of Classical

Conditioning • Establishing a Classically

Conditioned Response • Classical Conditioning in

Humans • Classical Conditioning Is

Selective

Operant Conditioning • Elements of Operant

Conditioning • Establishing an Operantly

Conditioned Response • A Closer Look at

Reinforcement • Punishment • Learned Helplessness • Shaping Behavioral Change

Through Biofeedback

Factors Shared by Classical and Operant Conditioning • The Importance of

Contingencies • Extinction and Spontaneous

Recovery • Stimulus Control,

Generalization, and Discrimination

O V E R V I E W

• New Learning Based on Original Learning

• Summing Up Cognitive Learning • Latent Learning and

Cognitive Maps • Insight and Learning Sets • Learning by Observing • Cognitive Learning in

Nonhumans

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define it more broadly. To them, learning occurs whenever experience or practice results in a relatively permanent change in behavior or in potential behavior. This definition includes all the examples previously mentioned, plus a great many more. When you remember how to park a car or where the library water fountain is, you are showing a tiny part of your enormous capacity for learning.

Human life would be impossible without learning; it is involved in virtually everything we do. You could not communi- cate with other people or recognize yourself as human if you were unable to learn. In this chapter, we explore several kinds of learning. One type is learning to associate one event with another. When pouched rats associate the smell of TNT and receiving food or when a person associates the sight or smell of a food with illness they are engaging in two forms of learning called operant and classical conditioning. Because psycholo- gists have studied these forms of learning so extensively, much of this chapter is devoted to them. But making associations isn’t all there is to human learning. Our learning also involves the for- mation of concepts, theories, ideas, and other mental abstrac- tions. Psychologists call it cognitive learning, and we discuss it at the end of this chapter.

Our tour of learning begins in the laboratory of a Nobel Prize–winning Russian scientist at the turn of the 20th century. His name is Ivan Pavlov, and his work is helping to rev- olutionize the study of learning. He has discovered classical conditioning.

ENDURING ISSUES IN LEARNING This chapter addresses how humans and other animals acquire new behaviors as a result of their experiences. Thus, it bears directly on the enduring issue of Stability versus Change (the extent to which organisms change over the course of their lives). The events that shape learning not only vary among different individuals (diversity–universality) but also are influenced by an organism’s inborn characteristics (nature–nurture). Finally, some types of learning can affect our physical health by influencing how our body responds to disease (mind–body).

CLASSICAL CONDITIONING How did Pavlov discover classical conditioning?

The Russian physiologist Ivan Pavlov (1849–1936) discovered classical (or Pavlovian) conditioning, a form of learning in which a response elicited by a stimulus becomes elicited by a previously neutral stimulus, almost by accident. He was studying digestion, which begins when saliva mixes with food in the mouth. While measuring how much saliva dogs produce when given food, he noticed that they began to salivate even before they tasted the food. The mere sight of food or the sound of his footsteps made them drool. This aroused Pavlov’s curiosity. How had the dogs learned to salivate to sights and sounds?

L E A R N I N G O B J E C T I V E S • Define learning. • Describe the elements of classical

conditioning, distinguishing between unconditioned stimulus, unconditioned response, conditioned stimulus and conditioned response. Describe the process of establishing a classically conditioned response, including the effect of intermittent pairing.

• Provide examples of classical conditioning in humans, including desensitization therapy. Explain the statement that “classical conditioning is selective” and illustrate with examples of conditioned taste aversions.

• In Mozambique, a giant pouched rat the size of a cat scurries across a field, pauses, sniffs the air, turns,

sniffs again, and then begins to scratch at the ground with her forepaws. She has discovered yet another land mine buried a few inches underground. After a brief break for a bit of banana and a pat or two from her handler, she scur- ries off again to find more land mines.

• In the middle of a winter night, Adrian Cole—4 years old and three feet tall—put on his jacket and boots and drove his mother’s car to a nearby video store. When he found the store closed, he drove back home. Since he was driving very slowly with the lights off and was also weaving a bit, he understandably attracted the attention of police officers who followed him. When he got home, he collided with two parked cars and then backed into the police cruiser! When the police asked him how he learned to drive, he explained that his mother would put him on her lap while she drove and he just watched what she did.

• “I just can’t stand to eat shrimp. I don’t like the smell of it, or the sight of it. Once when I young, I had some for dinner while vacationing at the beach and it made me sick for the rest of the week. Now just the thought of it disgusts me.”

The common element in all these stories—and the topic of this chapter—is learning. Although most people associate learning with classrooms and studying for tests, psychologists

What do the following anecdotes have in common? IS

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learning The process by which experience or practice results in a relatively permanent change in behavior or potential behavior.

classical (or Pavlovian) conditioning The type of learning in which a response naturally elicited by one stimulus comes to be elicited by a different, formerly neutral, stimulus.

unconditioned stimulus (US) A stimulus that invariably causes an organism to respond in a specific way.

unconditioned response (UR) A response that takes place in an organism whenever an unconditioned stimulus occurs.

conditioned stimulus (CS) An originally neutral stimulus that is paired with an unconditioned stimulus and eventually produces the desired response in an organism when presented alone.

conditioned response (CR) After conditioning, the response an organism produces when a conditioned stimulus is presented.

Figure 5–1 Pavlov’s apparatus for classically conditioning a dog to salivate. The experimenter sits behind a one-way mirror and controls the presentation of the conditioned stimulus (touch applied to the leg) and the unconditioned stimulus (food). A tube runs from the dog’s salivary glands to a vial, where the drops of saliva are collected as a way of measuring the strength of the dog’s response.

To answer this question, Pavlov sounded a bell just before presenting his dogs with food. A ringing bell does not usually make a dog’s mouth water, but after hearing the bell many times right before getting fed, Pavlov’s dogs began to salivate as soon as the bell rang. It was as if they had learned that the bell signaled the appearance of food; and their mouths watered on cue even if no food followed. The dogs had been conditioned to salivate in response to a new stimulus: the bell, which normally would not prompt salivation (Pavlov, 1927). Figure 5–1 shows one of Pavlov’s procedures in which the bell has been replaced by a touch to the dog’s leg just before food is given.

Elements of Classical Conditioning How might you classically condition a pet?

Figure 5–2 diagrams the four basic elements in classical conditioning: the unconditioned stimulus, the unconditioned response, the conditioned stimulus, and the conditioned response. The unconditioned stimulus (US) is an event that automatically elicits a certain reflex reaction, which is the unconditioned response (UR). In Pavlov’s studies, food in the mouth was the unconditioned stimulus, and salivation to it was the unconditioned response. The third element in classical conditioning, the conditioned stimulus (CS), is an event that is repeatedly paired with the unconditioned stimulus. For a conditioned stimu- lus, Pavlov often used a bell. At first, the conditioned stimulus does not elicit the desired response. But eventually, after repeatedly being paired with the unconditioned stimulus, the conditioned stimulus alone comes to trigger a reaction similar to the unconditioned response. This learned reaction is the conditioned response (CR).

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Classical conditioning has been demonstrated in virtually every animal species, even cockroaches, bees, and sheep (Abramson & Aquino, 2002; Johnson, Stanton, Goodlett, & Cudd, 2008; Krasne & Glanzman, 1995; Watanabe, Kobayashi, Sakura, Matsumoto, & Mizunami, 2003; Watanabe & Mizunami, 2006). You yourself may have inadvertently clas- sically conditioned one of your pets. For instance, you may have noticed that your cat begins to purr when it hears the sound of the electric can opener running. For a cat, the taste and smell of food are unconditioned stimuli for a purring response. By repeatedly pairing the can opener whirring with the delivery of food, you have turned this sound into a conditioned stimulus that triggers a conditioned response.

Establishing a Classically Conditioned Response If you once burned your finger on a match while listening to a certain song, why doesn’t that song now make you reflexively jerk your hand away?

As shown in Figure 5–3, it generally takes repeated pairings of an unconditioned stimulus and a cue before the unconditioned response eventually becomes a conditioned response. The likelihood or strength of the conditioned response increases each time these two stim- uli are paired. This learning, however, eventually reaches a point of diminishing returns. The amount of each increase gradually becomes smaller, until finally no further learning occurs. The conditioned response is now fully established.

It is fortunate that repeated pairings are usually needed for clas- sical conditioning to take place (Barry Schwartz, 1989). There are always a lot of environmental stimuli present whenever an uncondi- tioned stimulus triggers an unconditioned response. If conditioning occurred on the basis of single pairings, all these usually irrelevant stimuli would generate some type of CR. Soon we would be over- whelmed by learned associations. Because a number of pairings are usually needed to produce a conditioned response, only a cue con- sistently related to the unconditioned stimulus typically becomes a conditioned stimulus.

In cr

ea se

in st

re ng

th o

f C R

Number of trials

Figure 5–3 Response acquisition. At first, each pairing of the US and CS increases the strength of the response. After a number of trials, learning begins to level off; and eventually it reaches a point of diminishing returns.

Bell USUS

USUS

URUR

CRCR

CSCS

CSCS

No response

(Food) (Salivation)

URUR (Salivation)(Food)(Bell)

(Bell) (Salivation)

Before conditioning

During conditioning

After conditioning

but

Followed by

Figure 5–2 A model of the classical conditioning process.

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desensitization therapy A conditioning technique designed to gradually reduce anxiety about a particular object or situation.

Desensitization therapy is based on the belief that we can overcome fears by learning to remain calm in the face of increasingly fear- arousing situations. Here people being desensitized to a fear of heights are able to swing high above the ground without panicking.

The spacing of pairings is also important in establishing a classically conditioned response. If pairings of the CS and US follow each other very rapidly, or if they are very far apart, learning the association is slower. If the spacing of pairings is moderate—neither too far apart nor too close together—learning occurs more quickly. It is also important that the CS and US rarely, if ever, occur alone. Pairing the CS and US only once in a while, called intermittent pairing, reduces both the rate of learning and the final strength of the learned response.

Classical Conditioning in Humans What is an example of classical conditioning in your own life?

Classical conditioning is as common in humans as it is in other animals. For example, some people learn phobias through classical conditioning. Phobias are intense, irrational fears of particular things or situations, such as spiders or flying. In Chapter 1, we discussed the study in which John Watson and his assistant, Rosalie Rayner, used classical conditioning to instill a phobia of white rats in a 1-year-old baby named Little Albert (J. B. Watson & Rayner, 1920). They started by pairing a loud noise (an unconditioned stimulus) with the sight of a rat. After a few pairings of the rat and the frightening noise, Albert would cry in fear at the sight of the rat alone.

Several years later, psychologist Mary Cover Jones demonstrated a way that fears can be unlearned by means of classical conditioning (M. C. Jones, 1924). Her subject was a 3- year-old boy named Peter who, like Albert, had a fear of white rats. Jones paired the sight of a rat with an intrinsically pleasant experience—eating candy. While Peter sat alone in a room, a caged white rat was brought in and placed far enough away so that the boy would not be frightened. At this point, Peter was given candy to eat. On each successive day, the cage was moved closer, after which, Peter was given candy. Eventually, he showed no fear of the rat, even without any candy. By being repeatedly paired with a stimulus that evoked a pleasant emotional response, the rat had become a conditioned stimulus for pleasure.

In more recent times, psychiatrist Joseph Wolpe (1915–1997) adapted Jones’s method to the treatment of certain kinds of anxiety (Wolpe, 1973, 1990). Wolpe reasoned that because irrational fears are learned (conditioned), they could also be unlearned through conditioning. He noted that it is not possible to be both fearful and relaxed at the same time. Therefore, if people could be taught to relax in fearful or anxious situations, their anxiety should disappear. Wolpe’s desensitization therapy begins by teaching a system of deep-muscle relaxation. Then the person constructs a list of situations that prompt various degrees of fear or anxiety, from intensely frightening to only mildly so. A person with a fear of heights, for example, might construct a list that begins with standing on the edge of the Grand Canyon and ends with climbing two rungs on a ladder. While deeply relaxed, the person imagines the least distressing situation on the list first. If he or she succeeds in remaining relaxed, the person proceeds to the next item on the list, and so on until no anx- iety is felt. In this way, classical conditioning is used to change an undesired reaction: A fear-arousing thought is repeatedly paired with a muscular state that produces calmness until eventually the formerly fearful thought no longer triggers anxiety. Desensitization therapy has been used successfully to treat a variety of disorders such as phobias and post- traumatic stress disorder (Morris, Kratochwill, Schoenfield, & Auster, 2008; S. M. Silver, Rogers, & Russell, 2008). More recently, desensitization therapy has taken on a new form using virtual reality simulation. For instance, a person with a fear of flying may learn to relax while in a flight simulator rather than actually aboard an airplane. Therapy using vir- tual reality desensitization is still in its infancy, but the early results are promising (Parsons & Rizzo, 2008).

intermittent pairing Pairing the conditioned stimulus and the unconditioned stimulus on only a portion of the learning trials.

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preparedness A biological readiness to learn certain associations because of their survival advantages.

conditioned taste aversion Conditioned avoidance of certain foods even if there is only one pairing of conditioned and unconditioned stimuli.

Classical Conditioning Is Selective Why are people more likely to develop a phobia of snakes than of flowers?

If people can develop phobias through classical conditioning, why don’t we acquire phobias of virtually everything that is paired with harm? For example, many people get shocks from electric sockets, but almost no one develops a socket phobia. Why should this be the case?

Psychologist Martin Seligman (1971) has offered an answer: The key, he says, lies in the concept of preparedness. Some things readily become conditioned stimuli for fear responses because we are biologically prepared to learn those associations. Among the common objects of phobias are heights, snakes, and the dark. In our evolutionary past, fear of these potential dangers probably offered a survival advantage, and so a readiness to form such fears may have become “wired into” our species.

Preparedness also underlies conditioned taste aversion, a learned association between the taste of a certain food and a feeling of nausea and revulsion. Conditioned taste aver- sions are acquired very quickly. It usually takes only one pairing of a distinctive flavor and subsequent illness to develop a learned aversion to the taste of that food. Readily learning connections between distinctive flavors and illness has clear benefits. If we can quickly learn which foods are poisonous and avoid those foods in the future, we greatly increase our chances of survival. Other animals with a well-developed sense of taste, such as rats and mice, also readily develop conditioned taste aversions, just as humans do (Chester, Lumeng, Li, & Grahame, 2003; Guitton, Klin, & Dudai, 2008).

Mind–Body Classical Conditioning and the Immune System In another example of classical conditioning in humans, researchers have devised a novel way to treat autoimmune disorders, which cause the immune system to attack healthy organs or tissues. Although powerful drugs can be used to suppress the immune system and thus reduce the impact of the autoimmune disorder, these drugs often have dangerous side effects, so they must be administered sparingly. The challenge, then, was to find a treat- ment that could suppress the immune system without damaging vital organs. Researchers discovered that they could use formerly neutral stimuli either to increase or to suppress the activity of the immune system (Hollis, 1997; Markovic, Dimitrijevic, & Jankovic, 1993). Here’s how it works: As US, the researchers use immune-suppressing drugs and pair them with a specific CS, such as a distinctive smell or taste. After only a few pairings of the drug (US) with the smell or taste (CS), the CS alone suppresses the immune system (the CR) without any dangerous side effects! In this case, classical conditioning works on the mind but ultimately affects the body. While the use of classical conditioning to treat autoimmune disorders shows promise, additional research is still necessary to validate its effectiveness and evaluate its potential application as a therapy to treat these disorders (Bovbjerg, 2003; Gregory Miller & Cohen, 2001). ■

Nature–Nurture The Evolutionary Basis of Fear To what extent does our evolutionary heritage condition our fears; and to what extent are fears the result of our experiences? Recent studies suggest that the two work in tandem (Mineka & Oehman, 2002). For example, some stimuli unrelated to human survival through evolution, but which we have learned to associate with danger, can serve as CSs for

A bird’s nervous system is adapted to remem- ber sight–illness combinations, such as the distinctive color of a certain berry and subse- quent food poisoning. In mammals, by con- trast, taste–illness combinations are quickly and powerfully learned.

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fear responses. Pictures of handguns and butcher knives, for example, are as effective as pic- tures of snakes and spiders in conditioning fear in some people (Lovibond, Siddle, & Bond, 1993). These studies suggest that preparedness may be the result of learning rather than evolution. Other studies have shown that people who do not suffer from phobias can rather quickly unlearn fear responses to spiders and snakes if those stimuli appear repeatedly without painful or threatening USs (Honeybourne, Matchett, & Davey, 1993). Thus, even if humans are prepared to fear these things, that fear can be overcome through conditioning. In other words, our evolutionary history and our personal learning histories interact to increase or decrease the likelihood that certain kinds of conditioning will occur. ■

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OPERANT CONDITIONING How are operant behaviors different from the responses involved in classical conditioning?

Around the turn of the 20th century, while Pavlov was busy with his dogs, the American psychologist Edward Lee Thorndike (1874–1949) was using a “puzzle box,” or simple wooden cage, to study how cats learn (Thorndike, 1898). As illustrated in Figure 5–4,

___ unconditioned stimulus a. bell ___ unconditioned response b. food ___ conditioned stimulus c. salivating to bell ___ conditioned response d. salivating to food

CHECK YOUR UNDERSTANDING

1. The simplest type of learning is called ____________ ____________. It refers to the establishment of fairly predictable behavior in the presence of well-defined stimuli.

2. Match the following in Pavlov’s experiment with dogs:

3. The intense, irrational fears that we call phobias can be learned through classical conditioning. Is this statement true (T) or false (F)?

4. A learned association between the taste of a certain food and a feeling of nausea is called ____________ ____________ ____________.

5. Teaching someone to relax even when he or she encounters a distressing situation is called ____________ ____________.

6. In the experiment with Little Albert, the unconditioned stimulus was __________ ___________.

Answers:1. classical conditioning.2. unconditioned stimulus—b; unconditioned response—d; conditioned stimulus—a; conditioned response—c.3. T.4. conditioned taste aversion.5. desensitization therapy.6. loud noises.

APPLY YOUR UNDERSTANDING

1. Which of the following are examples of classical conditioning? a. eating when not hungry just because we know it is lunchtime b. a specific smell triggering a bad memory c. a cat running into the kitchen to the sound of a can opener d. All of the above are examples of classical conditioning.

2. You feel nauseated when you read about sea scallops on a restaurant menu, because you once had a bad episode with some scallops that made you sick. For you in this situation, the menu description of the scallops is the

a. US. b. CS. c. CR.

Answers:1. d.2. b.

Seligman’s theory of preparedness argues that we are biologically prepared to associ- ate certain stimuli, such as heights, the dark, and snakes, with fear responses. In our evo- lutionary past, fear of these potential dangers probably offered a survival advantage.

L E A R N I N G O B J E C T I V E S • Explain how operant conditioning

differs from classical conditioning. • Explain the law of effect (the principle

of reinforcement) and the role of reinforcers, punishers, and shaping in establishing an operantly conditioned response. Differentiate between positive reinforcers, negative reinforcers, and punishment. Explain the circumstances under which punishment can be effective and the drawbacks to using punishment.

• Explain what is meant by learned helplessness.

• Describe how biofeedback and neurofeedback can be used to change behavior.

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Thorndike confined a hungry cat in the puzzle box, with food just outside where the cat could see and smell it. To get to the food, the cat had to figure out how to open the latch on the box door, a process that Thorndike timed. In the beginning, it took the cat quite a while to discover how to open the door. But on each trial, it took the cat less time, until eventually it could escape from the box in almost no time at all. Thorndike was a pioneer in studying the kind of learning that involves making a certain response due to the consequences it brings. This form of learning has come to be called operant or instrumental conditioning. The pouched rat described at the opening of this chapter learned to find land mines through operant conditioning.

Elements of Operant Conditioning What two essential elements are involved in operant conditioning?

One essential element in operant conditioning is emitted behavior. This is one way in which operant conditioning is different from classical conditioning. In classical conditioning, a response is automatically triggered by some stimulus, such as a loud noise automatically triggering fear. In this sense, classical conditioning is passive in that the behaviors are elicited by stimuli. However, this process is not true of the behaviors involved in operant conditioning. Thorndike’s cats spontaneously tried to undo the latch on the door of the box. You spontaneously wave your hand to signal a taxi to stop. You voluntarily put money into machines to obtain food. These and similar actions are called operant behaviors because they involve “operating” on the environment.

A second essential element in operant conditioning is a consequence following a behav- ior. Thorndike’s cats gained freedom and a piece of fish for escaping from the puzzle boxes. Consequences like this one, which increase the likelihood that a behavior will be repeated, are called reinforcers. In contrast, consequences that decrease the chances that a behavior will be repeated are called punishers. Imagine how Thorndike’s cats might have acted had they been greeted by a large, snarling dog when they escaped from the puzzle boxes. Thorndike summarized the influence of consequences in his law of effect: Behavior that brings about a satisfying effect (reinforcement) is likely to be performed again, whereas

operant (or instrumental) conditioning The type of learning in which behaviors are emitted (in the presence of specific stimuli) to earn rewards or avoid punishments.

operant behaviors Behaviors designed to operate on the environment in a way that will gain something desired or avoid something unpleasant.

reinforcers A stimuli that follows a behavior and increases the likelihood that the behavior will be repeated.

punishers Stimuli that follows a behavior and decreases the likelihood that the behavior will be repeated.

law of effect (principle of reinforcement) Thorndike’s theory that behavior consistently rewarded will be “stamped in” as learned behavior, and behavior that brings about discomfort will be “stamped out.”

5 252015 Number of trials

Ti m

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The cat can escape and be rewarded with food by tripping the bolt on the door.

Cats learned to make the necessary response more rapidly after an increasing numbers of trials.

Figure 5–4 A cat in a Thorndike “puzzle box.” The cat can escape and be rewarded with food by tripping the bolt on the door. As the graph shows, Thorndike’s cats learned to make the necessary response more rapidly after an increasing number of trials.

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Figure 5–5 A rat in a Skinner box. By pressing the bar, the rat releases food pellets into the box; this procedure reinforces its bar- pressing behavior.

behavior that brings about a negative effect (punishment) is likely to be suppressed. Contemporary psychologists often refer to the principle of reinforcement, rather than the law of effect, but the two terms mean the same thing.

Establishing an Operantly Conditioned Response

How might an animal trainer teach a tiger to jump through a flaming hoop?

Because the behaviors involved in operant conditioning are voluntary ones, it is not always easy to establish an operantly conditioned response. The desired

behavior must first be performed spontaneously in order for it to be rewarded and strengthened. Sometimes you can simply wait for this action to happen.

Thorndike, for example, waited for his cats to trip the latch that opened the door to his puzzle boxes. Then he rewarded them with fish. But when there are many opportunities for making irrelevant responses, waiting can

be slow and tedious. If you were an animal trainer for a circus, imagine how long you would have to wait for a tiger to decide to jump through a flaming hoop so you could reward it. One way to speed up the process is to increase motivation. Even without food in sight, a hungry animal is more active than a well-fed one and so is more likely, just by chance, to make the response you’re looking for. Another strategy is to reduce opportuni- ties for irrelevant responses, as Thorndike did by making his puzzle boxes small and bare. Many researchers do the same thing by using Skinner boxes to train small animals in. A Skinner box (named after B. F. Skinner, another pioneer in the study of operant condition- ing), is a small cage with solid walls that is relatively empty, except for a food cup and an activating device, such as a bar or a button. (See Figure 5–5.) In this simple environment, it doesn’t take long for an animal to press the button that releases food into the cup, thereby reinforcing the behavior.

Usually, however, the environment cannot be controlled so easily; hence a different approach is called for. Another way to speed up operant conditioning is to reinforce succes- sive approximations of the desired behavior. This approach is called shaping. To teach a tiger to jump through a flaming hoop, the trainer might first reinforce the animal simply for jumping up on a pedestal. After that behavior has been learned, the tiger might be rein-

forced only for leaping from that pedestal to another. Next, the tiger might be required to jump through a hoop between the pedestals to gain a reward. And finally, the hoop is set on fire, and the tiger must leap through it to be rewarded.

As in classical conditioning, the learning of an operantly conditioned response eventually reaches a point of diminishing returns. If you look back at Figure 5–4, you’ll see that the first few reinforce- ments produced quite large improvements in per- formance, as indicated by the rapid drop in time required to escape from the puzzle box. But each successive reinforcement produced less of an effect until, eventually, continued reinforcement brought no evidence of further learning. After 25 trials, for instance, Thorndike’s cats were escaping from the box no more quickly than they had been after 15 trials. The operantly conditioned response had then been fully established. Can operant conditioning

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positive reinforcers Events whose presence increases the likelihood that ongoing behavior will recur.

negative reinforcers Events whose reduction or termination increases the likelihood that ongoing behavior will recur.

influence human behavior? See “Applying Psychology: Modifying Your Behavior,” above, to learn about how you can use operant conditioning to modify your own behavior.

Remember that the new, more desirable behavior need not be learned all at once. You can use shaping or successive approximations to change your behavior bit by bit. A person who wants to become more sociable might start by giving rewards just for sitting next to another person in a classroom rather than picking an isolated seat. The person could then work up to rewarding increasingly sociable behaviors, such as first saying hello to another person, then striking up a conversation.

A Closer Look at Reinforcement What is the difference between positive and negative reinforcement? What are some of the unintentional effects that reinforcement can have?

We have been talking about reinforcement as if all reinforcers are alike, but in fact this is not the case. Think about the kinds of consequences that would encourage you to perform some behavior. Certainly these include consequences that give you something positive, like praise, recognition, or money. But the removal of some negative stimulus is also a good reinforcer of behavior. When new parents discover that rocking a baby will stop the infant’s persistent crying, they sit down and rock the baby deep into the night; the removal of the infant’s crying is a powerful reinforcer.

These examples show that there are two kinds of reinforcers. Positive reinforcers, such as praise, add something rewarding to a situation, whereas negative reinforcers, such as

Skinner box A box often used in operant conditioning of animals; it limits the available responses and thus increases the likelihood that the desired response will occur.

shaping Reinforcing successive approximations to a desired behavior.

Modifying Your Own Behavior

Can you modify your own undesirablebehaviors by using operant condi-tioning techniques? Yes, but first you must observe your own actions, think about their implications, and plan a strat- egy of intervention.

1. Begin by identifying the behavior you want to acquire: This is called the “target” behavior. You will be more successful if you focus on acquiring a new behavior rather than on elimi- nating an existing one. For example, instead of setting a target of being less shy, you might define the target behavior as becoming more outgoing or more sociable.

2. The next step is defining the target behavior precisely: What exactly do you mean by “sociable”? Imagine sit- uations in which the target behavior could be performed. Then describe in writing the way in which you now

respond to these situations. For example, you might write, “When I am sitting in a lecture hall, waiting for class to begin, I don’t talk to the people around me.” Next, write down how you would rather act in that sit- uation: “In a lecture hall before class, I want to talk to at least one other person. I might ask the person sitting next to me how he or she likes the class or the professor or simply com- ment on some aspect of the course.”

3. The third step is monitoring your present behavior: You may do so by keeping a daily log of activities related to the target behavior. This will establish your current “base rate” and give you something concrete against which to gauge improve- ments. At the same time, try to figure out whether your present, undesir- able behavior is being reinforced in some way. For example, if you find

yourself unable to study, record what you do instead (Get a snack? Watch television?) and determine whether you are inadvertently rewarding your failure to study.

4. The next step—the basic principle of self-modification—is providing your- self with a positive reinforcer that is contingent on specific improvements in the target behavior: You may be able to use the same reinforcer that now maintains your undesirable behavior, or you may want to pick a new reinforcer. For example, if you want to increase the amount of time you spend studying, you might reward yourself with a token for each 30 minutes of study. Then, if your favorite pastime is watching movies, you might charge yourself three tokens for an hour of television, whereas the privilege of going to a movie might cost six.

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punishment Any event whose presence decreases the likelihood that ongoing behavior will recur.

The use of punishment has potential draw- backs. It cannot “unteach” unwanted behav- ior, only suppress it. Punishment may also stir up negative feelings in the person who is punished or inadvertently provide a model of aggressive behavior.

stopping an aversive noise, subtract something unpleasant. Animals will learn to press bars and open doors not only to obtain food and water (positive reinforcement), but also to turn off a loud buzzer or an electric shock (negative reinforcement).

Both positive and negative reinforcement results in the learning of new behaviors or the strengthening of existing ones. Remember, in everyday conversation when we say that we have “reinforced” something, we mean that we have strengthened it. Similarly, in oper- ant conditioning, reinforcement—whether positive or negative—always strengthens or encourages a behavior. A child might practice the piano because she or he receives praise for practicing (positive reinforcement) or because it gives her or him a break from doing tedious homework (negative reinforcement), but in either case the end result is a higher incidence of piano playing.

But what if a particular behavior is just accidentally reinforced because it happens by chance to be followed by some rewarding incident? Will the behavior still be more likely to occur again? B. F. Skinner (1948) showed that the answer is yes. He put a pigeon in a Skin- ner box and at random intervals dropped a few grains of food into the food cup. The pigeon began repeating whatever it had been doing just before the food was given, such as standing on one foot. This action had nothing to do with getting the food, of course. But still the bird repeated it over and over again. Skinner called the bird’s behavior superstitious, because it was learned in a way that is similar to how some human superstitions are learned (Aeschleman, Rosen, & Williams, 2003). If you happen to be wearing an Albert Einstein T- shirt when you get your first A on an exam, you may come to believe that wearing this shirt was a factor. Even though the connection was pure coincidence, you may keep on wearing your “lucky” shirt to every test thereafter.

In the case of forming superstitions, reinforcement has an illogical effect on behavior, but that effect is generally harmless. Some psychologists believe that reinforcement can also lead inadvertently to negative results. They believe that offering certain kinds of reinforcers (candy, money, play time) for a task that could be intrinsically rewarding (that is, reinforc- ing in and of itself) can undermine the intrinsic motivation to perform it. People may begin to think that they are working only for the reward and lose enthusiasm for what they are doing. They may no longer see their work as an intrinsically interesting challenge in which to invest creative effort and strive for excellence. Instead, they may see work as a chore that must be done to earn some tangible payoff. This warning can be applied to many situations, such as offering tangible rewards to students for their work in the classroom, or giving employees a “pay for performance” incentive to meet company goals (Kohn, 1993; Rynes, Gerhart, & Parks, 2005).

Other psychologists, however, suggest that this concern about tangible reinforcers may be exaggerated. Although the use of rewards may sometimes produce negative outcomes, this is not always the case (Cameron, Banko, & Pierce, 2001). In fact, one extensive review of more than 100 studies showed that when used appropriately, rewards do not compro- mise intrinsic motivation, and under some circumstances, they may even help to encourage creativity (Eisenberger & Cameron, 1996; Selarta, Nordström, Kuvaas, & Takemura, 2008). For example, research has shown that rewarding highly creative behavior on one task often enhances subsequent creativity on other tasks (Eisenberger & Rhoades, 2001).

Punishment What problems can punishment create?

Although we all hate to be subjected to it, punishment is a powerful controller of behavior. After receiving a heavy fine for failing to report extra income to the IRS, we are less likely to make that mistake again. In this case, an unpleasant consequence reduces the likelihood that we will repeat a behavior. This is the definition of punishment.

Punishment is different from negative reinforcement. Reinforcement of whatever kind strengthens (reinforces) behavior. Negative reinforcement strengthens behavior by remov- ing something unpleasant from the environment. In contrast, punishment adds something unpleasant to the environment; and as a result, it tends to weaken the behavior that caused

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it. If going skiing during the weekend rather than studying for a test results in getting an F, the F is an unpleasant consequence (a punisher) that makes you less likely to skip homework for ski time again.

Is punishment effective? We can all think of instances when it doesn’t seem to work. Children often continue to misbehave even after they have been punished repeatedly for that particular misbe- havior. Some drivers persist in driving recklessly despite repeated fines. Why are there these seeming exceptions to the law of effect? Why, in these cases, isn’t punishment having the result it is supposed to?

For punishment to be effective, it must be imposed properly (Gershoff, 2002). First, punish- ment should be swift. If it is delayed, it doesn’t work as well. Sending a misbehaving child immediately to a time-out seat (even when it is not convenient to do so) is much more effective than waiting for a “better” time to punish. Punishment should also be sufficient without being cruel. If a parent briefly scolds a child for hitting other children, the effect will probably be less pronounced than if the child is sent to his or her room for the day. At the same time, punishment should be consistent. It should be imposed for all infractions of a rule, not just for some.

Punishment is particularly useful in situations in which a behavior is dangerous and must be changed quickly. A child who likes to poke things into electric outlets, or runs out into a busy street must be stopped immediately, so punishment may be the best course of action. But even in situations like these, punishment has drawbacks (Gershoff, 2002; B. F. Skinner, 1953).

Punishment Cannot Unteach Unwanted Behaviors First, it only suppresses the undesired behavior; it doesn’t prompt someone to “unlearn” the behavior, and it doesn’t teach a more desirable one. If the threat of punishment is removed, the negative behavior is likely to recur. This result is apparent on the highway. Speeders slow down when they see a police car (the threat of punishment), but speed up again as soon as the threat is passed. Punishment, then, rarely works when long-term changes in behavior are wanted (Pogarsky & Piquero, 2003).

Punishment Can Backfire Second, punishment often stirs up negative feelings (frus- tration, resentment, self-doubt), which can impede the learning of new, more desirable behaviors. For example, when a child who is learning to read is scolded for every mispro- nounced word, the child may become very frustrated and hesitant. This frustration and doubt about ability can prompt more mispronunciations, which lead to more scolding. In time, the negative feelings that punishment has caused can become so unpleasant that the child may avoid reading altogether. In addition, some studies have shown that children who frequently experience corporal punishment have a higher incidence of depression, antisocial behavior, decreased self-control, and increased difficulty relating to their peers (C. E. Leary, Kelley, Morrow, & Mikulka, 2008; Slessareva & Muraven, 2004).

Punishment Can Teach Aggression. A third drawback of punishment, when it is harsh, is the unintended lesson that it teaches: Harsh punishment may encourage the learner to copy that same harsh and aggressive behavior toward other people (Gershoff, 2002). In laboratory studies, monkeys that are harshly punished tend to attack other mon- keys (Barry Schwartz, 1989). In addition, punishment often makes people angry, aggres- sive, and hostile (Lansford et al., 2005; Mathurin, Gielen, & Lancaster, 2006).

Because of these drawbacks, punishment should be used carefully, and always together with reinforcement of desirable behavior. Once a more desirable response is established, punishment should be removed to reinforce negatively that new behavior. Positive rein-

Corporal Punishment

Some school systems still use some form of corporal punishment, such as pad-dling, for students who misbehave. The justification is that it is an effectivemethod of changing undesirable behavior, it develops a sense of personal responsibility, it teaches self-discipline, and it helps develop moral character.

Based on what you now know about operant conditioning,

1. under what circumstances (if any) should corporal punishment be used in schools?

2. what factors, besides the student’s immediate actions, should adults consider before using corporal punishment?

3. what unintended consequences might arise from the use of corporal punishment?

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forcement (praise, rewards) should also be used to strengthen the desired behavior because it teaches an alternative behavior to replace the punished one. Positive reinforcement also makes the learning environment less threatening.

Sometimes, after punishment has been administered a few times, it needn’t be contin- ued, because the mere threat of punishment is enough to induce the desired behavior. Psy- chologists call it avoidance training, because the person is learning to avoid the possibility of a punishing consequence. Avoidance training is responsible for many everyday behav- iors. It has taught you to keep your hand away from a hot iron to avoid the punishment of a burn. Avoidance training, however, doesn’t always work in our favor. For instance, a child who has been repeatedly criticized for poor performance in math may learn to shun diffi- cult math problems in order to avoid further punishment. Unfortunately, the child fails to develop math skills and therefore fails to improve any innate capabilities, and so a vicious cycle has set in. The avoidance must be unlearned through some positive experiences with math in order for this cycle to be broken.

Diversity–Universality What Is Punishment? We do not know whether something is reinforcing or punishing until we see whether it increases or decreases the occurrence of a response. We might also assume that having to work alone, rather than in a group of peers, would be punishing, but some children prefer to work alone. Teachers must understand the children in their classes as individuals before they decide how to reward or punish them. Similarly, what is reinforcing for people in one culture might not have the same effect for people in other cultures.

In addition, an event or object might not be consistently rewarding or punishing over time. So even if candy is initially reinforcing for some children, if they eat large amounts of it, it can become neutral or even punishing. We must therefore be very careful in labeling items or events as “reinforcers” or “punishers.” ■

Learned Helplessness In what ways do some college students exhibit learned helplessness?

Have you ever met someone who has decided he will never be good at science? We have said that through avoidance training, people learn to prevent themselves from being punished, but what happens when such avoidance of punishment isn’t possible? The answer is often a “giving-up” response that can generalize to other situations. This response is known as learned helplessness.

Martin Seligman and his colleagues first studied learned helplessness in experiments with dogs (Seligman & Maier, 1967). They placed two groups of dogs in chambers that delivered a series of electric shocks to the dogs’ feet at random intervals. The dogs in the control group could turn off (escape) the shock by pushing a panel with their nose. The dogs in the experimental group could not turn off the shock—they were, in effect, helpless. Next, both the experimental and the control animals were placed in a different situation, one in which they could escape shock by jumping over a hurdle. A warning light always came on 10 seconds before each 50-second shock was given. The dogs in the control group quickly learned to jump the hurdle as soon as the warning light flashed, but the dogs in the experimental group didn’t. These dogs, which had previously experienced unavoidable shocks, didn’t even jump the hurdle after the shock started. They just lay there and accepted the shocks. Also, many of these dogs were generally listless, suffered loss of appetite, and displayed other symptoms associated with depression.

Many subsequent studies have shown that learned helplessness can occur both in ani- mals and in humans (G. W. Evans & Stecker, 2004; C. Peterson, Maier, & Seligman, 1993b;

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avoidance training Learning a desirable behavior to prevent the occurrence of something unpleasant, such as punishment.

learned helplessness Failure to take steps to avoid or escape from an unpleasant or aversive stimulus that occurs as a result of previous exposure to unavoidable painful stimuli.

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biofeedback A technique that uses monitoring devices to provide precise information about internal physiological processes, such as heart rate or blood pressure, to teach people to gain voluntary control over these functions.

neurofeedback A biofeedback technique that monitors brain waves with the use of an EEG to teach people to gain voluntary control over their brain wave activity.

Overmier, 2002). Once established, the condition generalizes to new situations and can be very persistent, even given evidence that an unpleasant circumstance can now be avoided (C. Peterson, Maier, & Seligman, 1993a). For example, when faced with a series of unsolv- able problems, a college student may eventually give up trying and make only halfhearted efforts to solve new problems, even when the new problems are solvable. Moreover, success in solving new problems has little effect on the person’s behavior. He or she continues to make only halfhearted tries, as if never expecting any success at all. Similarly, children raised in an abusive family, where punishment is unrelated to behavior, often develop a feeling of helplessness (C. Peterson & Bossio, 1989). Even in relatively normal settings out- side their home, they often appear listless, passive, and indifferent. They make little attempt either to seek rewards or to avoid discomfort.

Shaping Behavioral Change Through Biofeedback How can operant conditioning be used to control biological functions?

Patrick, an 8-year-old third grader, was diagnosed with attention-deficit disorder (ADD). He was unable to attend to what was going on around him, was restless, and was unable to con- centrate. An EEG showed increased numbers of slow brain waves. After a course of 40 training sessions using special computer equipment that allowed Patrick to monitor his brain-wave activities, he learned how to produce more of the fast waves that are associated with being calm and alert. As a result, Patrick became much more “clued in” to what was going on around him and much less likely to become frustrated when things didn’t go his way (Fitzgerald, 1999; Fuchs, Birbaumer, Lutzenberger, Gruzelier, & Kaiser, 2003; Monas- tra, 2008).

When operant conditioning is used to control certain biological functions, such as blood pressure, skin temperature or heart rate, it is referred to as biofeedback. Instruments are used to measure particular biological responses—muscle contractions, blood pressure, heart rate. Variations in the strength of the response are reflected in signals, such as light or tones. By using these signals, the person can learn to control the response through shaping. For example, Patrick learned to control his brain waves by controlling the movement of a Superman icon on a computer screen. When biofeedback is used to monitor and control brain waves, as in Patrick’s case, it is referred to as neurofeedback (Butnik, 2005).

Biofeedback and neurofeedback have become well-established treatments for a number of medical problems, including migraine headaches (Kropp, Siniatchkin, & Gerber, 2005), hypertension (Rau, Buehrer, & Weitkunat, 2003; Reineke, 2008), and panic attacks (Meuret, Wilhelm, & Roth, 2004). Biofeedback has also been used by athletes, musi- cians, and other performers to control the anxiety that can interfere with their performance.

Biofeedback treatment does have some draw- backs. Learning the technique takes considerable time, effort, patience, and discipline. And it does not work for everyone. But it gives many patients control of their treatment, a major advantage over other treatment options, and it has achieved impressive results in alleviating certain medical problems (Olton & Noonberg, 1980).

Biofeedback and Neurofeedback

Assume for the moment that you are skeptical about the benefits ofbiofeedback and neurofeedback. What questions would you ask aboutresearch studies that claim to show they are beneficial? To get started, refer back to Chapter 1 and the section on “Critical Thinking.”

1. What kind of evidence would you look for to support your skeptical posi- tion? What kind of evidence would cause you to rethink your position? Are you swayed by reports of single cases (such as Patrick) or would you be more influenced by studies of large numbers of people? Would you be interested in short-term effects, or would you want to see results over a much longer period of time?

2. What assumptions would you need to watch out for? How would you know whether biofeedback or neurofeedback really worked? (Remember that you should be skeptical of self-reports.)

3. Might there be alternative explanations for the results of the research you find? In other words, is it possible that something quite apart from biofeedback or neurofeedback could explain the results?

4. Once you have formulated your position on the benefits of biofeedback or neurofeedback, how would you avoid oversimplifying your conclusions?

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L E A R N I N G O B J E C T I V E S • Describe the importance of

contingencies in both operant and classical conditioning.

• Differentiate between the four schedules of reinforcement in operant conditioning and their effect on learned behavior.

• Describe the processes of extinction, spontaneous recovery, generalization, and discrimination in classical and operant conditioning.

• Explain what is meant by higher order conditioning and differentiate between primary and secondary reinforcers.

CHECK YOUR UNDERSTANDING

1. An event whose reduction or termination increases the likelihood that ongoing behavior will recur is called ____________ reinforcement, whereas any event whose presence increases the likelihood that ongoing behavior will recur is called ____________ reinforcement.

2. A type of learning that involves reinforcing the desired response is known as ____________ ____________.

3. When a threat of punishment induces a change to more desirable behavior, it is called ____________ ____________.

4. Superstitious behavior can result when a behavior is rewarded by pure ____________. 5. Any stimulus that follows a behavior and decreases the likelihood that the behavior will be

repeated is called a ____________. 6. Which of the following problems may result from avoidance training?

a. A person may continue to avoid something that no longer needs to be avoided. b. The effects of avoidance training tend to last for only a short time. c. Avoidance training may produce latent learning. d. Avoidance training tends to take effect when it is too late to make a difference in

avoiding the problem situation.

Answers:1. negative; positive.2. operant conditioning.3. avoidance training. 4. coincidence.5. punishment.6. a.

APPLY YOUR UNDERSTANDING

1. Imagine that you want to teach a child to make his or her bed. What kind of reinforcement could you use to do that?

a. punishment b. positive reinforcement c. negative reinforcement d. both (b) and (c) would work

2. You are hired to make a commercial for a company that manufactures dog food. They want you to get a dog to run from a hallway closet, under a coffee table, around a sofa, leap over a wagon, rush to the kitchen, and devour a bowl of dog food. The most effective way to accomplish this task would be to

a. wait for this chain of events to happen and then use a reinforcer to increase the likelihood that the behavior will occur again on demand.

b. use shaping. c. teach the dog to discriminate between the various landmarks on its way to

the food. d. hire a smart dog. Answers:1. d.2. b.

FACTORS SHARED BY CLASSICAL AND OPERANT CONDITIONING Can you think of any similarities between classical and operant conditioning?

Despite the differences between classical and operant conditioning, these two forms of learning have many things in common. First, they both involve the learning of associations. In classical conditioning, it is a learned association between one stimulus and another, whereas in operant conditioning, it is a learned association between some action and a consequence. Second, the responses in both classical and operant conditioning are under the control of stimuli in the environment. A classically conditioned fear might be triggered by the sight of a white rat; an operantly conditioned jump might be cued by the flash of a red light. In both cases, moreover, the learned responses to a cue can generalize to similar stimuli. Third, neither classically nor operantly conditioned responses will last forever if

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contingency A reliable “if–then” relationship between two events, such as a CS and a US.

blocking A process whereby prior conditioning prevents conditioning to a second stimulus even when the two stimuli are presented simultaneously.

they aren’t periodically renewed. This doesn’t necessarily mean that they are totally forgot- ten, however. Even after you think that these responses have long vanished, either one can suddenly reappear in the right situation. And fourth, in both kinds of learning—classical and operant conditioning—new behaviors can build on previously established ones.

The Importance of Contingencies How can changes in the timing of a conditioned stimulus lead to unexpected learning? Why does intermittent reinforcement result in such persistent behavior?

Because classical and operant conditioning are both forms of associative learning, they both involve perceived contingencies. A contingency is a relationship in which one event depends on another. Graduating from college is contingent on passing a certain number of courses. In both classical and operant conditioning, perceived contingencies are very important.

Contingencies in Classical Conditioning In classical conditioning, a contingency is perceived between the CS and the US. The CS comes to be viewed as a signal that the US is about to happen. This is why, in classical conditioning, the CS not only must occur in close proximity to the US, but also should precede the US and provide predictive informa- tion about it (Rescorla, 1966, 1967, 1988).

Scientists once believed that no conditioning would occur if the CS followed the US; this belief, however, turns out not to be entirely true. The explanation again lies in contin- gency learning. Imagine a situation in which a tone (the CS) always follows a shock (the US). This process is called backward conditioning. After a while, when the tone is sounded alone, the learner will not show a conditioned fear response to it. After all, the tone has never predicted that a shock is about to be given. But what the learner does show is a condi- tioned relaxation response to the sound of the tone, because the tone has served as a signal that the shock is over and will not occur again for some time. Again, we see the importance of contingency learning: The learner responds to the tone on the basis of the information that it gives about what will happen next.

Other studies similarly show that predictive information is crucial in establishing a classically conditioned response. In one experiment with rats, for instance, a noise was repeatedly paired with a brief electric shock until the noise soon became a conditioned stimulus for a conditioned fear response (Kamin, 1969). Then a second stimulus—a light—was added right before the noise. You might expect that the rat came to show a fear of the light as well, because it, too, preceded the shock. But this is not what happened. Apparently, the noise–shock contingency that the rat had already learned had a blocking effect on learning that the light also predicted shock. Once the rat had learned that the noise signaled the onset of shock, adding yet another cue (a light) provided no new predic- tive information about the shock’s arrival, and so the rat learned to ignore the light (Kruschke, 2003). Classical conditioning, then, occurs only when a stimulus tells the learner something new or additional about the likelihood that a US will occur.

Contingencies in Operant Conditioning Contingencies also figure prominently in operant conditioning. The learner must come to perceive a connection between per- forming a certain voluntary action and receiving a certain reward or punishment. If no contingency is perceived, there is no reason to increase or decrease the behavior.

But once a contingency is perceived, does it matter how often a consequence is actually delivered? When it comes to rewards, the answer is yes. Fewer rewards are often better than more. In the language of operant conditioning, partial or intermittent reinforcement results in behavior that will persist longer than behavior learned by continuous reinforcement. Why would this be the case? The answer has to do with expectations. When people receive only

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schedule of reinforcement In operant conditioning, the rule for determining when and how often reinforcers will be delivered.

fixed-interval schedule A reinforcement schedule in which the correct response is reinforced after a fixed length of time since the last reinforcement.

variable-interval schedule A reinforcement schedule in which the correct response is reinforced after varying lengths of time following the last reinforcement.

Table 5–1 EXAMPLES OF REINFORCEMENT IN EVERYDAY LIFE

Continuous reinforcement (reinforcement every time the response is made)

Putting money in a parking meter to avoid getting a ticket. Putting coins in a vending machine to get candy or soda.

Fixed-ratio schedule (reinforcement after a fixed number of responses)

Being paid on a piecework basis. In the garment industry, for example, workers may be paid a fee per 100 dresses sewn.

Variable-ratio schedule (reinforcement after a varying number of responses)

Playing a slot machine. The machine is programmed to pay off after a certain number of responses have been made, but that number keeps changing. This type of schedule creates a steady rate of responding, because players know that if they play long enough, they will win. Sales commissions. You have to talk to many customers before you make a sale, and you never know whether the next one will buy. The number of sales calls you make, not how much time passes, will determine when you are reinforced by a sale, and the number of sales calls will vary.

Fixed-interval schedule (reinforcement of first response after a fixed amount of time has passed)

You have an exam coming up, and as time goes by and you haven’t studied, you have to make up for it all by a certain time, and that means cramming. Picking up a salary check, which you receive every week or every 2 weeks.

Variable-interval response (reinforcement of first response after varying amounts of time)

Surprise quizzes in a course cause a steady rate of studying because you never know when they’ll occur; you have to be prepared all the time. Watching a football game; waiting for a touchdown. It could happen anytime. If you leave the room, you may miss it, so you have to keep watching continuously.

Source: From Landy, 1987, p. 212. Adapted by permission.

fixed-ratio schedule A reinforcement schedule in which the correct response is reinforced after a fixed number of correct responses.

variable-ratio schedule A reinforcement schedule in which a varying number of correct responses must occur before reinforcement is presented.

extinction A decrease in the strength or frequency, or stopping, of a learned response because of failure to continue pairing the US and CS (classical conditioning) or withholding of reinforcement (operant conditioning).

occasional reinforcement, they learn not to expect reinforcement with every response, so they continue responding in the hopes that eventually they will gain the desired reward. Vending machines and slot machines illustrate these different effects of continuous versus partial reinforcement. A vending machine offers continuous reinforcement. Each time you put in the right amount of money, you get something desired in return (reinforcement). If a vending machine is broken and you receive nothing for your coins, you are unlikely to put more money in it. In contrast, a casino slot machine pays off intermittently; only occasion- ally do you get something back for your investment. This intermittent payoff has a com- pelling effect on behavior. You might continue putting coins into a slot machine for a very long time even though you are getting nothing in return.

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