What is Associative Learning?

Learning may be defined broadly as a stable change within an organism caused by an experience or set of experiences — a change that is reflected in changes behaviors, thoughts, and/or emotions. We are members of a species, Homo sapiens[∂], that has evolved in ways that allow most of us to be very aware of and very good at learning about our environments. Humans probably learn much more about more diverse aspects of the environment — and to do so more easily — than any other species that has ever existed. Thus, early experimental psychologists focused much of their research on understanding human learning. The doctrine of associationism gave them a way of conceptualizing the learning process: learning involves the formation of associations between events — between mental events in structuralism, and between environmental events in behaviorism. This type of learning is known as "associative learning"[∂]. Some psychologists and biologists study nonassociative learning[∂], such as habituation, which is decreased responsiveness to a frequently repeated stimulus. For example, when a fan turns on in a ventilation system while you are sitting in a quiet room, you may be startled by it at first but, eventually, you stop noticing it. Although nonassociative learning is very important in our everyday lives, most experimental psychologists and other behavioral scientists have focused on associative learning in their research.

Let's look at an example of associative learning. Let’s say that a friend invites you to dinner at an expensive restaurant. After eating a very large and calorie-rich meal, you drink too much of a sweet-tasting liqueur. Although you feel happy and content for an hour or so, you eventually become nauseous and then begin to vomit. A few weeks later, you smell something similar to the smell of the liqueur, instantly feel an emotion of disgust, and begin gagging. The experience in which the gustatory [∂] and olfactory[∂] sensations of the liqueur were paired with the somatic[∂], gustatory, and olfactory sensations of nausea and vomiting has caused changes in your cognitions, emotions, and behaviors: you now are digusted and become physically ill by sensations similar to those you experienced when you drank the liqueur several weeks before. These cognitive, emotional, and behavioral changes are caused by a type of associative learning called classical conditioning.

[NOTE: IN FUTURE, ADD SELYE— FIGHT OR FLIGHT; Theories of Emotion. xxx James (1884)]

What is Classical Conditioning?

Behaviorists defined classical conditioning as a procedure in which a neutral stimulus — a stimulus that initially does not elicit a specific automatic (involuntary) response — is followed repeatedly by a reflexive stimulus — a stimulus that elicits a specific automatic (involuntary) response (that is, a reflex). in Figure 1 is llustrated the procedure of classical conditioning:

Figure 1. An Outline of the Classical Conditioning Procedure.

Associationists assumed that the repeated pairing of the neutral stimulus with the reflexive stimulus causes a change in the central nervous systems of organisms (Pavlov, 1927). This change may be conceived of in the following way:

(a) The presentation of the neutral stimulus activates a particular area of the CNS. The subsequent presentation of the reflexive stimulus activates a second area of the CNS. Because of an already existing neural connection, the activation of the area linked to the reflexive stimulus causes the activation of the area that produces the reflexive response (see Figure 2).

Figure 2. Activation of CNS Areas Associated With the Neutral
Stimulus, the Reflexive Stimulus, and the Reflexive Response.

(b) The repeated presentation of the neutral stimulus followed immediately by the reflexive stimulus causes the development of a new neural connection between the two CNS areas activated by the stimuli (see Figure 3).

Figure 3. The Establishment of a Neural Connection Between
the CNS Area Activated by the Neutral Stimulus and the CNS
Area Activated by the Reflexive Stimulus.

(c) Associationists assumed that this new neural connection forms the physical basis of the association learned in classical conditioning. Thus, when the area linked to the neutral stimulus is activated by the presentation of the neutral stimulus, the area linked to the reflexive stimulus becomes almost immediately activated through the activation of the new neural connection.

(d) Once the new neural connection has developed, the reflexive stimulus no longer is needed to elicit the reflexive response: the presentation of the (formerly) neutral stimulus now can activate the area linked to the reflexive stimulus, thereby causing the activation of the area linked to the reflexive response, which elicits that response.

According to the associationist view, therefore, the learning of an association between the neutral stimulus and the reflexive stimulus is passive and machine-like: the close pairing in time of stimuli changes the CNS automatically. Thus, associationists claimed that organisms (including humans) have no active role in what they learn: conscious thinking and reasoning is not necessary for the learning of a new way of responding to environmental events.

Terminology
In the terminology of classical conditioning, the neutral stimulus is referred to as the conditioned stimulus. The word "conditioned" means "learned," so we can think of the conditioned stimulus (abbreviated CS) as the stimulus that the organism learns to respond to involuntarily when followed repeatedly by a second stimulus that already elicits an involuntary response (see Figure 4). This second stimulus is referred to as the unconditioned stimulus. The word "unconditioned" means "unlearned," so we can think of the unconditioned stimulus (abbreviated UCS) as the stimulus that the organism already responds to involuntarily because it is part of a reflex.

Figure 4. An Outline of the Classical Conditioning Procedure
Using the Terminology of Behaviorism.

In defining "conditioned" as "learned," we can see that the conditioned response (abbreviated CR) is the response that the organism learns to produce involuntarily when presented with a conditioned stimulus (but only after the conditioned stimulus has become associated with an unconditioned stimulus). Lastly, in defining "unconditioned" as "unlearned," it follows that the unconditioned response (abbreviated UCR) is the reflexive response produced involuntarily by the unconditioned stimulus.

One example of classical conditioning was described in Section 3-1: newborn infants salivate reflexively to the taste of their mother’s milk. In classical conditioning terminology, the taste of mother's milk is the UCS that elicits the involuntary response of salivation, which is the UCR. The UCS is preceded each time by the sight of an approaching nipple. Since the baby does not initially salivate to the sight of the nipple, this stimulus is the CS (the initially neutral stimulus). The repeated pairing of the CS and the UCS eventually leads to the development of an association between the two stimuli. We know that a CS-UCS association has formed when the baby salivatates to the CS (the sight of the nipple). This learned salivation is the CR. Figure 4 illustrates this example:

Figure 5. The Classical Conditioning of Salivation
to the Sight of the Mother's Nipple.

The development of new physiological responses, such as salivation, often can be explained by classical conditioning. Classical conditioning, as well as other types of learning to be described in later sections, also have been used to explain the development of mental disorders characterized primarily by anxiety, irritability, and depression — the kinds of mental disorders referred to by psychodynamic theorists as neuroses[∂] (see Dollard & Miller, 1950). One common type of neurosis is phobic disorder, which will be described next.

Study Questions

1. How would you define learning in your own words?
2. What are some examples of learning not mentioned in the textbook?
3. What is the major distinction between associative and nonassociative learning?
4. What is habituation?
5. What is classical conditioning?
6. How does habituation differ from classical conditioning?
7. What is being associated in classical  conditioning?
8. How do you know when an association has been formed in classical conditioning?
9. According to the early associationists, what is the physical basis of the association formed in classical conditioning?
10. According to the early associationists, what role does the human conscious mind have in what is learned through classical conditioning?
11. What are two examples of classical conditioning from your everyday life?
12. In each of your examples, what is the CS, the UCS, the CR, and the UCR?

Can Classical Conditioning Explain the Development of Phobias?

A phobia is a persistent and irrational fear of an object, situation, or activity. To be considered "irrational," the degree of fear must be much greater than is warranted by the actual danger posed by the object, situation, or activity. For example, a person who refuses to go into basements because there may be spiders "down there," would be suffering from a phobia. Furthermore, except in cases of young children, the person must realize to some extent that the amount of fear is unwarranted by the actual danger. (If the person thinks that his or her irrational fear actually is rational and warranted, we would conclude that the person is suffering from a delusion[∂].) In 1909, Sigmund Freud published a case study of a four-year-old boy, whom he called “Little Hans,” with a severe phobia[∂] of horses. Hans's father described the boy’s problems in a letter he sent to Freud:

during the last few days [Little Hans] has developed a nervous disorder, which has made my wife and me most uneasy, because we have not been able to find any means of dissipating it. ... He is afraid that a horse will bite him in the street” (quoted in Spitzer, et al., 1994, p. 517).

It seems that Hans' fear first emerged while he was walking down a city street with his mother and saw a large horse fall down and begin to kick violently. Freud provided a psychoanalytic explanation of the development of Hans' phobia, which will be described in Section 6. But, since, you are learning about classical conditioning in this section, how might we use this learning process to explain the development of Hans' phobia?

Was Hans always afraid of horses? No, he apparently first became afraid of them only after seeing and hearing a large horse fall and kick violently in the street while walking with his mother. Thus, in the terminology of classical conditioning, the sight and sound of a horse was, for Hans, a conditioned stimulus (CS). The sight and sound of a large horse falling and then struggling to get up, as well as the commotion that this would have caused among people nearby, would have been sufficient to frighten any child: no learning would have been needed to elicit this distressing emotion involuntarily. Thus, the sight and sound of the tumultuous situation surrounding the fallen horse was, for Hans, an unconditioned stimulus (UCS). The reflexive distress automatically elicited by this frightening situation was an unconditioned response (UCR); and the learned distress that came to be automatically elicited by the sight of horses was the conditioned response (CR). The acquisition of the CR was caused by the development of an association between the CS and the UCS during the walk with his mother. The relationships among the stimuli and responses in this explanation of the development of Little Hans' horse phobia are presented in Figure 6.

Figure 6. Classical Conditioning Terminology as Applied in the
Behavioristic Explanation of the Case of Little Hans

Thus, it is possible to explain Freud's famous case as an instance of classical conditioning: a verifiable environmental event (the street scene with the fallen horse) can be used to explain the development of a verifiable set of behaviors (Hans' symptoms of phobia).

In fact, John Watson and Rosalie Rayner (1920) argued that the psychoanalytic theory that phobias primarily are the result of unconscious conflicts is inferior to the behavioristic theory that classical conditioning plays the primary role in the development of phobias:

It is probable that many of the phobias in psychopathology are true conditioned emotional reactions.... One may possibly have to believe that such persistence of early conditioned responses will be found only in persons who are constitutionally inferior. Our argument is meant to be constructive. Emotional disturbances in adults cannot be traced back to sex alone. They must be retraced along at least three collateral lines — to conditioned ... responses set up in infancy and early youth in all three of the fundamental human emotions [fear, rage and love] (p. 14).

One reason for concluding that the psychoanalytic theory is inferior to the behavioristic theory is that psychoanalysts need to make more assumptions[∂] than do the behaviorists. For example, the psychoanalytic approach assumes that:

• humans inherit memories of traumatic events experienced by our ancestors;
• trivial early-childhood experiences have large influences because they activate these memories;
• these influences involve an active unconscious mind that is the primary determinant of personality;
• repression occurs because of conflicts between biological motives linked to these inherited memories and constraints on the satisfaction of these motives;
• the ego must use energy to keep these repressed conflicts at the unconscious level;
• the repressed conflicts are expressed in abnormal behaviors;
• and so on.

The behavioristic approach, on the other hand, assumes that:

• humans develop associations between stimuli that are paired closely in time;
• the physical nature of this association involves the development of new CNS connections;
• the new CNS connections cause organisms to respond reflexively to previously neutral stimuli.

When comparing two or more theories, it generally is best to evaluate more favorably the theory making the fewest assumptions: the greater the number of untested (and, therefore, questionable) claims in a theory, the greater is the probability that at least one of these claims will be wrong. This prescript[∂] is known as the "rule of simplicity."

The rule of simplicity states that, when two theories make the same predictions and explain the evidence equally well, the theory that makes the fewest assumptions is more likely to be true. This rule (supposedly) was summed up by Albert Einstein, who reportedly said: "Everything should be made as simple as possible, but not simpler" (quoted in Gibbs & Hiroshi, 1997). Watters & Ofhse (1999) provided another way to think of the rule of simplicity: "When you hear hooves, think horses, not zebras" (p. 222). The point here is that one should consider the most plausible[∂] theories first, which tend to be those theories that make the fewest assumptions. For example, if a teacher is trying to explain why a student looks like she is asleep during class, the teacher should assume that the student actually is asleep and that she is sleeping because she is tired. It seems unreasonable for the teacher to assume that the student is only pretending to be sleeping because she is, for some unknown reason, angry with him and thinks that, by pretending to be asleep, he will feel bad because he then will think that he is a boring teacher. Although possibly true, this second theory includes more untested assumptions — assumptions at least one of which may turn out to be wrong.

Study Questions

13. How can the development of Little Hans' horse phobia be explained by classical conditioning?
14. What advantage does the classical-conditioning theory of the development of Little Hans' horse phobia have over the psychoanalytic theory?
15. How would you define the rule of simplicity in your own words?
16. What is an example of your use of the rule of simplicity in your everyday life?
17. How might the rule of simplicity mislead us when trying to explain a phenomenon?

What Happened to Little Albert?

John Watson believed that humans are born with the ability to emotionally respond involuntarily to only a few stimuli (for example, babies may feel joy when held but not when they are the winners of an enormous cash prize) and that, over the course of our lives, we acquire the ability to emotionally respond involuntarily to an enormous range of other stimuli. For instance, babies respond involuntarily with distress to an unexpected loud noise — an emotional response that typically is coupled with characteristic movements and intense crying. On the other hands, babies don't respond with anxiety to the sight of a police car driving behind them, although their parents probably do. According to Watson, the fact that adults respond involuntarily with anxiety to a larger number of stimuli than babies do is due to classical conditioning: initially neutral stimuli were paired with other stimuli that involuntarily elicited anxiety because of inborn reflexes. In other words, Watson argued that the pairing, over our lifespans, of a large number of CSs with a smaller number of inborn UCSs is the major determinant of the emotional development of humans.

In order to test his theory, Watson and Rayner (1920) classically conditioned an emotional response of anxiety in an infant they dubbed “Little Albert,” perhaps as a nod to Freud's case study of "Little Hans." Because Albert was less than one year old, he had not yet developed fear responses to many of the objects often feared by older children. For example, he showed no fear of a white rat when presented with one. In order to see if they could get Albert to fear the rat, Watson and Rayner subjected him to the following classical-conditioning procedure (see Figure 7):

Figure 7. The Classical Conditioning Procedure
as Applied to the Case of Little Albert

Although Albert initially showed no signs of anxiety to the rat (the CS), when a metal bar was struck with a hammer directly behind his head, thereby causing an unexpected loud noise (the UCS), Albert responded involuntarily with signs of severe distress (the UCR). After several pairings of the CS and the UCS, Albert developed an involuntary response of anxiety (the CR) to the sight of the rat alone. According to Watson and Rayner, Albert's anxiety had been conditioned to a new stimulus.

This interpretation of Watson’s and Rayner’s (1920) study formed the basis for the behavioristic theory of the development of phobias. For example, let’s consider the case of a man who is terrified by flies. It makes no sense to be terrified by flies since flies generally cause no harm (except in rare cases in which they carry harmful diseases). How might classical conditioning cause the development of this phobia? Figure 8 presents one possibility:

Figure 8. Classical Conditioning of a Fly Phobia.

In this case, perhaps when he was a boy, the man stumbled upon a smelly and bloody animal carcass buzzing with flies. Startled by the sudden appearance of the decaying body, he felt terror and disgust; and, because the carcass was covered with flies, these two events became associated for him. Later, when seeing and hearing flies, he involuntarily felt a learned terror and disgust to this stimulus. Of course, there are other possibilities for how a fly phobia might develop through classical conditioning. Regardless of the specifics of how such a phobia might develop through classical conditioning, there are two essential points to remember:

• When a neutral stimulus is followed repeatedly by a second stimulus that reflexively elicits an emotional response, a learned emotional response that is automatically elicited by the first stimulus may develop because of the development of an association between the two stimuli.
• 4This learning process may lead, in some circumstances, to the development of a mental disorder in which strong emotions are automatically elicited inappropriately by stimuli that would not typically elicit them.

Watson, of course, thought that his theory of conditioned fears (phobias) was superior to that developed by Freud and others. In fact, Watson and Rayner (1920) suggested (probably "tongue-in-cheek") that the:

Freudians twenty years from now, unless their hypotheses change, when they come to analyze Albert's fear of a seal skin coat — assuming that he comes to analysis at that age — will probably tease from him the recital of a dream which upon their analysis will show that Albert at three years of age attempted to play with the pubic hair of the mother and was scolded violently for it. (We are by no means denying that this might in some other case condition it). If the analyst has sufficiently prepared Albert to accept such a dream when found as an explanation of his avoiding tendencies, and if the analyst has the authority and personality to put it over, Albert may be fully convinced that the dream was a true revealer of the factors which brought about the fear. (p. 14)

Here, Watson & Rayner were referring to the verifiability problem inherent in the psychoanalytic approach — a problem that they believed had been overcome in the behavioristic approach. They seem to be suggesting that, whereas psychoanalysis might be the approach to adopt if one wishes to hear "fairy tales" about the causes of neuroses, behaviorism is the approach to adopt if one wishes to find the real causes of these mental disorders.

Study Questions

18. What was the theory that Watson and Rayner (1920) were testing in their study of Little Albert?
19. Did Little Albert fear rats at the beginning of the study?
20. Why did Little Albert fear rats at the end of the study? (In your answer, please give details of the procedure used with him)
21. How did behaviorists explain the development of mental disorders involving severe disturbances in emotion?
22. What did Watson think was wrong with the psychoanalytic approach to explaining neurotic disorders such as phobias?

The Acquisition, Extinction, & Spontaneous Recovery of CRs
Let’s consider further the classical conditioning of anxiety in a person. Let's say that a rat (the CS) is paired with a loud noise (the UCS), which reflexively produces an anxiety response (the UCR), on each of ten trials (a trial is a single presentation of a CS or a CS-UCS pairing), with each trial separated by one hour. Furthermore, let's suppose that this procedure is used to classically condition 100 people. On average, their anxiety to the rat (the CR) should increase over the ten trials. The initial learning of the association between the CS and UCS, which is indicated by the development of a CR, is called the acquisition phase of classical conditioning. This phase is represented in the first ten trials of Figure 9.

Figure 9. Acquisition, Extinction, & Spontaneous Recovery in Classical Conditioning.

Have you ever wondered why advertisers show the same commercial over-and-over again? One reason is that it involves a number of pairings of the CS (their product) with the UCS (perhaps a popular celebrity) to acquire the CR (positive feelings for their product). (See Behaviorism & Advertising.) But a number of CS-UCS pairings is not always needed for a strong CR to be acquired. In fact, an association may develop even after only one CS-UCS pairing. For example, one pairing of a bee (the CS) with a bee sting (the UCS) often is all that is required for a child to learn to fear bees (the CR).

After acquisition of the CR, you may wonder whether it is necessary to continue pairing the CS and UCS. If the CS now reflexively elicits the CR — if a new reflex has been learned — perhaps the UCS is no longer needed to maintain the CR. What would happen if we discontinued the UCS? In most cases, we would find that the CR declines over trials after the UCS is removed. Eventually, the CR typically disappears (see Trials 11-20 in Figure 9). Thus, if the individual is going to continue to show a CR, the CS must continue to be paired with the UCS. The decline of the CR in the absence of the UCS is known as the extinction phase of classical conditioning.

Does the extinction of a CR mean that the association between the CS and UCS acquired earlier now has disappeared? For example, if Little Albert had been presented with a rat alone until his conditioned anxiety response had disappeared, would his association of the rat with the loud noise have been eliminated (see Jones, 1924, for the results of a similar study)? Not necessarily. In fact, Figure 9 shows what often happens when researchers again present the CS some time after extinction has occurred (see Trials 21-25): many of them will again express the CR. In general, if a period of time has elapsed since the extinction phase, an extinguished CR will reappear in many individuals — a phenomenon called spontaneous recovery. Spontaneous recovery of a CR shows that the association between the CS and the UCS was not eliminated during extinction in these individuals.

If the individual was not “unlearning” the association between the CS and UCS during the extinction phase, then why did the individual's CR disappear? It’s hard to know for certain, but perhaps a more intuitive example might help us to understand what may be happening. When you hear someone yell the words “watch out,” what do you do? You probably feel frightened and then bend down while placing your hands over your head. Why do you do this? The words themselves (“watch out”) should not induce fear. In fact, they simply seem to be suggesting that you should be looking somewhere “out there.” Thus, you must have acquired this fear response from some prior experiences. One way this might have happened is illustrated in Figure 10:

Figure 10. Acquisition of An Anxiety Response to "Watch Out."

Thus, classical conditioning can explain the acquisition of a fear response to these words. This may or may not be how you acquired the response, but many people probably do acquire it in this way.

Now, how could we extinguish the CR in this case? In extinction, we present the CS all by itself on each trial. If we want to extinguish the fear response to these words, therefore, we would need to have someone yell, “watch out,” over and over again and make sure that nothing negative happened immediately afterwards. In fact, someone probably has done this to you at some point during childhood: children seem to enjoy scaring others and this is an easy way to do it. What happened to your learned fear in this case? It probably decreased and perhaps disappeared over the time period in which the other person continued to yell, “watch out.” In other words, the CR was extinguished. What would happen if this other person waited some time (perhaps an hour) and then yelled, “watch out,” again? If this has ever happened to you, you probably found that you again showed a fear response to the words. That is, you showed spontaneous recovery of the CR. So, what was going on “inside your head” while the fear response was being extinguished? You probably were merely suppressing (inhibiting) any observable fear during extinction, but this did not cause you to “unlearn” the association between the words and getting hit in the head. Extinction generally does not lead immediately to the elimination of an association between a CS and a UCS. On the other hand, if the extinction procedure is repeated on several occasions, elimination of the association probably will occur eventually.

What does this discussion of the acquisition and extinction of CRs suggest about therapy for phobias? If you were a therapist using the behavioristic approach, how would you help a client to get rid of his phobic fear of bees — a fear that first developed during childhood when he was stung in the foot? Based on the discussion of the extinction process, one would predict that having him experience bees (the CS) without being stung by them (the UCS) probably would decrease (and perhaps eliminate) his phobia. This type of therapy is called exposure therapy because clients are exposed repeatedly to a feared object, event, or situation until their anxiety is reduced or eliminated.

How would you use exposure therapy with your client? Perhaps you first could have him imagine being in a roomful of bees that never stung him. Then you might have him sit next to a cage of bees. Then you might have him wear protective clothing and go into an apiary (a place where beehives are kept for their honey). In general, you would need to find some ways of presenting the CS (bees) without the UCS (getting stung). His phobic symptoms should improve over time: of those who remain in exposure therapy, about 80% experience significant improvement.

What do you think might be a limitation of exposure therapy? There are several limitations: people may be too afraid to finish therapy, you can’t always prevent the UCS, etc. But probably the most important limitation is that, unless the person keeps re-experiencing the CS without the UCS, spontaneous recovery of the fear often occurs. If spontaneous recovery does occur, the CR will have to be re-extinguished. Eventually, however, providing such “booster sessions” leads to the elimination of the phobic fear in many people.

Study Questions

23. What is acquisition? Please give an example from your own life of the acquisition of a CR.
24. What is extinction? Please give an example from your own life of the extinction of a CR.
25. What is spontaneous recovery? Please give an example from your own life of the spontaneous recovery of a CR.
26. When would extinction lead to the elimination of the association between a CS and a UCS?
27. What type of phobia therapy for phobias makes use of the process of extinction?
28. How successful is this type of therapy?
29. What is a major limitation of this type of therapy?

Stimulus Generalization
In classical conditioning, individuals learn an association between a particular CS and a particular UCS. For instance, let's consider a boy who steps on a bee that then stings him on the foot. The CS, in this example, is the sight and sound of the bee, the UCS is the pain caused by the stinger, and the UCR is the distress elicited reflexively by the pain. Of course, we would expect that the boy would be afraid of this particular bee in the future since it is the bee that stung him! As you all know, however, bees die after stinging someone and, therefore, the boy's learned fear should die along with the bee. Nevertheless, this typically doesn't happen. In fact, the boy may become afraid of all bees — even bees from other species. Furthermore, he may fear stinging insects from distantly related species that look very little like the original bee species. Lastly, he may even develop a fear of harmless flies that have markings that resemble somewhat the original species of bee. In short, the initial experience may cause the boy to develop fears that include a broad range of flying-insect species. This phenomenon is known as stimulus generalization[∂], which is defined as the tendency for stimuli similar to a CS to also elicit a CR.

In the case of Little Albert, the baby who was classically conditioned to fear a white rat after the rat had been paired with an unexpected loud noise, Watson and Rayner (1920) reported that Albert showed a "transfer" of his learned anxiety to a rabbit, a dog, a seal-fur coat, a Santa Claus mask, and perhaps even Watson's hair (although his reactions to these objects were not always consistent, and the study itself did not include adequate controls for extraneous variables). In general, the classical conditioning theory of phobic disorder states that the learned fear to a CS generalizes (transfers) to other stimuli, with the most transfer occurring to stimuli that are most similar to the CS.

Stimulus Discrimination
Dogs learn to discriminate among the language sounds made by humans. For instance, a dog may learn that one sound, "sit," means one thing (perhaps the dog "thinks" in whatever way internal canine thought processes occur, "if I sit down, I will get a treat"), whereas it learns that a highly similar sound, "git!" means something very different ("if I don't leave now, I will be punished"). With respect to classical conditioning, stimulus discrimination[∂] refers to a procedure in which a stimulus that is similar to an established CS — and, therefore, that elicits a CR — is never followed by the UCS, thereby causing the CR to that stimulus to extinguish. For example, you may have learned to respond with anxiety (a CR) to a particular tone of voice (a CS) used by your parent when that tone, in the past, has been followed by an outburst of anger (a UCS). On the other hand, you also may have learned not to respond with anxiety to a very similar (but not identical) tone of voice used by that same parent because that only slightly different tone, in the past, was followed only by mock anger.

In general, the classical conditioning theory of phobic disorder states that individuals learn to discriminate between the CS, which often is followed by the UCS, from stimuli that are similar to it but are rarely or never followed by the UCS. For example, the boy whose fear of bees generalized to a broad range of flying insects eventually may learn to discriminate between harmless species of flies that have bee-like markings, on the one hand, and the species of bee that stung him, on the other hand. He would learn to discriminate the two stimuli if contact with the bee-like flies never was followed by a sting, whereas contact with the bees often often was followed by a sting.

Study Questions

30. How would you define stimulus generalization in your own words?
31. What is an example of stimulus generalization that you have experienced?
32. How might stimulus generalization be an adaptive characteristic?
33. How would you define stimulus discrimination in your own words?
34. What is an example of stimulus discrimination that you have experienced?
35. How might stimulus discrimination be an adaptive characteristic?

What is Biological Preparedness?

As stated in Section 3-1, many behaviorists assumed that inherited biological differences among different organisms were not important causes of behavioral differences. Instead, they assumed that most animal behavior is caused by learning involving past experiences. Thus, behaviorists asserted that behavioral differences among different species were the result of environmental differences, not inherited biological differences. In addition, behaviorists believed that associative learning works in the same way in every species. Thus, they assumed that they could study animals of any species (such as rats and pigeons) in order to discover general principles of learning that would be true for all species. And they also assumed that any animal from any species could learn to associate any two events that were presented together. In other words, behaviorists assumed that associations would occur equally well in any animal species regardless of the stimuli the researchers used.

Beginning around 1960, however, these assumptions and beliefs began to be seriously questioned by many psychologists. It started to become apparent that species differed in what and how they learned. For example, it should be obvious to those of you who own dogs and cats that these two species learn different things and learn in different ways. Dogs, for instance, can learn to do some things when their only reward is praise, whereas cats don’t seem to respond to praise at all. Martin Seligman (1970, 1971) argued that different species have evolved different learning abilities, an idea that he called biological preparedness. Biological preparedness can be defined as an innate (inborn) tendency to learn certain kinds of associations (between stimuli in classical conditioning, or between operant responses and consequences in operant conditioning). This idea leads to an obvious question: what causes a species to be biologically prepared to learn some associations but not others? Those who argue in favor of biological preparedness believe that each species has innate tendencies to learn associations that help its members to survive longer and reproduce more. In other words, they claim that natural selection of learning abilities has occurred so that each species has evolved the ability to learn certain associations more easily than others.

A possible example of the evolution of biological preparedness in humans may be seen in the development of phobias. It seems that we easily learn fears of objects or situations that probably were dangerous to our ancestors. For example, young children learn animal phobias very easily. In fact, the tendency to easily learn strong fears of animals begins at an age (about three years) during which children have become highly mobile — a characteristic that often results in their being some distance from the protection of adults. Why would this situation make it adaptive for them to learn animal phobias? Well, let’s describe the probable environment of our ancient hominid ancestors. They often lived in an arid environment in which there was a lack of cover coupled with the presence of large carnivorous animals. Children who walked away from their caretakers would have been very vulnerable to animal attacks because there were few places to escape and no adults nearby to fend off an attacking animal. Children who easily learned to be afraid of animals with which they had had a negative experience would have a strong advantage if they came upon a similar animal in the future. In this case, as soon as they saw or heard the animal, they would become fearful and would be more likely to quickly run back to an adult. If this ability to quickly learn animal phobias was associated with the genes inherited by the children, it could evolve by natural selection over generations: children without the ability would have been more likely to die than would those children with the ability. Eventually, all other things being equal, the ability to easily learn to fear animals would become a species-typical adaptation. The fact that many animal phobias disappear after about ten years of age also is consistent with this theory: by adolescence, humans are much better at knowing where danger may lurk as well as at defending themselves from attacks.

Another example of associative learning for which some have argued that we show a high degree of biological preparedness is taste aversion, a type of classical conditioning in which an individual learns to avoid the taste (and smell) of something that has been paired with sensations of nausea. For example, if you eat some tainted sausage and develop food poisoning several hours later, it is likely that you will avoid eating sausage in the future. In classical-conditioning terms, the learning would be outlined as follows:

Figure 11. The Classical Conditioning of Taste Aversion.

Taste aversion was investigated by John Garcia and his colleagues (REFERENCES) in a series of studies performed during the 1960s. Garcia had been studying the effects of radiation on rats. In his research, he used a strong dose of X-rays to irradiate the rats — a procedure which induced “radiation sickness.” Radiation sickness causes vomiting and sensations of nausea (along with other physical problems) after about eight hours. Garcia always irradiated the rats in a cage that contained a plastic water bottle, whereas the cage in which the rats lived contained a glass water bottle. He noticed that, after they had been irradiated, most rats would never again drink from the plastic water bottle even though they had drunk from it before they had been irradiated. Furthermore, although the rats seemed to avoid the water in the plastic water bottle, they continued to drink from the glass water bottle in their “home” cages.

What do you think might cause this change in behavior? The rats were drinking from a water bottle that gave a “plastic taste” to the water. While in the cage with the plastic water bottle, they were subjected to large doses of X-rays. Several hours later, they became “sick to their stomachs” and began to vomit. After all this, the rats refused to drink from the plastic water bottle when again placed in the cage. One could infer that the rats no longer liked the taste of the water and that, perhaps, they even felt “disgust” when they tasted the water. Such an emotional response could lead to a refusal to drink from the plastic water bottle. Thus, the easiest way to make sense of this change in behavior is to suppose that the rats had been classically conditioned to experience a negative emotional response (disgust) when tasting the water in the plastic water bottle:

Figure 12. Example of Garcia's Studies of Taste Aversion.

In taste-aversion conditioning, the animal learns to avoid a particular taste because it is paired with sensations of nausea. According to Garcia, humans and other mammals have evolved the ability to learn associations between tastes (smells) because this ability is adaptive and, therefore, has been naturally selected: if we did not learn quickly and strongly to associate particular tastes with getting nauseous, we would soon die.

NOTE: IN FUTURE, DISCUSS ARTICLE BY DAVEY, 1995, AND OTHER CRITIQUES

Study Questions

36. How would you define "biological preparedness" in your own words?
37. How is biological preparedness thought to be related to evolution and natural selection?
38. What are some reasons in support of the idea that humans (and other primates) may be biologically prepared to develop certain types of phobias through classical conditioning?
39. How would you define "taste aversion" in your own words?
40. What is an example of the learning of a taste aversion in your own life?
41. In the development of taste aversion, an individual is learning an association between what two events?
42. In what way is the learning of taste aversions adaptive for animals?
43. Is the fact that the learning of taste aversions can be shown to be adaptive proof that this ability must have evolved through natural selection? Why or why not?