300-400 words discussion on behaviorism OR cognitivism, psychology homework help

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For this discussion, please choose one of the two options: behaviorism or cognitivism. Taking on the role of either a behaviorist or a cognitivist, you will demonstrate your understanding of your chosen psychological view by explaining why your theory and its history are important for others to understand and apply.

  1. Based on your own experiences, the resources listed above, and the scholarly article analyze how learning and theory apply in real-life situations by listing the pros and cons of each.
  2. Provide evidence for your stance from your resources.
  3. Please describe two real-life scenarios you have experienced and explain how you applied these psychological principles to the personal, social, or educational issues you mention. Please do not share anything that you would be uncomfortable discussing in a public forum.
  4. Based on the camp you chose, continue to answer the following:

Additional behaviorist questions to consider:

  • Do you agree with the behaviorist view that learning can be described simply in terms of stimulus-response relationships?
  • Do you agree with the behaviorist view that learning only occurs if there is an outward manifestation? Why, or why not?
  • What are the potential advantages of defining learning as a change in behavior when considering your own career (or future career) and/or in your relationships?

Additional cognitivist questions to consider:

  • Do you agree with the cognitivist view that thinking is not a behavior but actually creates important implications affecting behavior
  • Why do cognitivists disagree with the behaviorist view that learning only occurs if there is an outward manifestation? What are the implications to the behavior(s) it identifies?
  • Cognitivism suggests that what we know to be true affects our behaviors and how we learn, What implications might this have in your own career (or future career) and/or in your relationships?

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3 Principles and Applications of Conditioning Learning Objectives After reading this chapter, you should be able to do the following: • Recognize the principles of contiguity, frequency, and intensity and realize the extent to which these principles are supported by experimental research. • Define the four basic paradigms of classical conditioning: delay conditioning, trace conditioning, simultaneous conditioning, and backward conditioning. • Explain the phenomenon of sensory preconditioning and consider why the simultaneous presentation of a CS and a US does not result in conditioning. • Understand Rescorla’s research on contingency, and its suggestion that conditioning requires more than just contiguity. • Describe Garcia and Koelling’s research on taste-aversion learning, focusing on its implications for the role of contiguity in conditioning and on the role of evolution in shaping conditioning. • Discuss Kamin’s discovery of blocking, how he provided a cognitive account based on the concept of surprise, and the implications of his work for contiguity. • Identify the specific applications of conditioning principles, specifically in terms of how they can be used to treat phobias, cigarette smoking, and alcoholism. lie6674X_03_c03_087-114.indd 87 3/14/12 4:15 PM CHAPTER 3 Section 3.1 The Laws of Association We have seen that classical conditioning is not confined to relatively innocuous behaviors such as salivation; classical conditioning affects some of the most important choices we make, including what foods we eat, whether we become addicted to drugs, and whether we feel certain emotions, such as fear or sexual arousal. If we understood the principles of conditioning, therefore, it might allow us not only to better understand our behavior but also, potentially, to change this behavior. Could we use conditioning, for example, to reduce our fear in situations where it incapacitates us (for example, in job interviews or dating)? Conversely, could we learn to increase our fear in situations where this emotion might be advantageous—for example, could a smoker who wanted to quit make smoking aversive by pairing the sensations of smoking with a painful consequence? In this chapter we will try to answer these questions. We will begin by reviewing laboratory research on what factors determine the strength of conditioning. We will then look at attempts to apply these principles to problems such as phobias and alcoholism. 3.1 The Laws of Association The British Associationists, sitting in their armchairs several centuries ago, identified a number of laws of association, of which the most important were contiguity, frequency, and intensity. We will begin our survey of the principles of conditioning by considering the extent to which these laws have been supported by experiments. Contiguity The most important principle of association was thought to be contiguity. The very concept of an association—a bond between two events that occur closely in time—implicitly assumes that contiguity is necessary, and considerable effort has been devoted to exploring the role of contiguity in classical conditioning. The CS–US Interval When played together as part of a piece, musical notes are contiguous: that is, they occur together in time. lie6674X_03_c03_087-114.indd 88 As with most other aspects of conditioning, Pavlov was the first to investigate the role of contiguity in establishing a strong conditioned response. He experimented with four different temporal arrangements between the CS and the US; Figure 3.1 shows all four paradigms. (In learning, the term paradigm is used to represent a standard or typical sequence of events.) In delay conditioning, once the CS came on, it remained on until the US was presented. In trace conditioning, the CS was terminated before the US began. 3/14/12 4:15 PM CHAPTER 3 Section 3.1 The Laws of Association Figure 3.1: Paradigms for four varieties of classical conditioning Delay conditioning US Trace conditioning US CS CS Simultaneous US conditioning CS Backward conditioning US CS Time Pavlov was the first to examine the role of contiguity and utilized four different temporal arrangements between the CS and the US. Here, the bars on the time line indicate periods during which a stimulus is presented. Pavlov found that delay conditioning produced the strongest responding. As the British Associationists would have predicted, Pavlov found that conditioning was much stronger in the delay conditioning model, where the CS preceded the US, but both were ultimately on at the same time. Subsequent research confirmed Pavlov’s findings. In a typical study, Moeller (1954) looked at the effects of the CS–US interval on GSR (galvanic skin response) conditioning. He used a trace conditioning procedure in which a brief burst of white noise (CS) was followed after a delay by a weak electric shock (US), with the interval between the onset of the CS and the onset of the US set at either 250, 450, 1,000, or 2,500 milliseconds (ms). Moeller’s results are illustrated in Figure 3.2, which shows that the strength of the conditioned response was greatest in the group with a 450ms gap, conditioning was weaker with a delay of 1,000 milliseconds (one second), and virtually no conditioning occurred when the delay was increased to 2,500 milliseconds. Both the optimum interval and the maximum interval that will sustain conditioning vary somewhat for different responses (see Cooper, 1991, for a discussion of why this might be), but as a general rule, the shorter the interval between the CS and US, the better the conditioning. lie6674X_03_c03_087-114.indd 89 3/14/12 4:15 PM CHAPTER 3 Section 3.1 The Laws of Association Figure 3.2: GSR conditioning as a function of the CS–US interval during training CR strength 4 3 2 1 0 0 250 450 1000 2500 CS-US interval (milliseconds) Moeller’s experiment in 1954 concluded that the shorter the interval between the CS and US, the better the conditioning. This was determined by using a trace conditioning procedure in which a burst of noise (CS) was followed by an electric shock (US). The interval between the CS and US was set at either 250, 450, 1,000, or 2,500 milliseconds. Source: Adapted from Moeller, 1954. Simultaneous and Backward Conditioning You might have noticed one aspect of the data in Figure 3.2 that does not support this claim, namely that when the CS–US interval was less than 450 ms, conditioning not only didn’t improve, it became worse. Other experiments confirmed this finding: When the CS and the US are presented in rapid succession, with delays of less than half a second, conditioning is usually poor. As with so many other aspects of conditioning, Pavlov was the first researcher to discover this anomaly. One might think that a simultaneous conditioning procedure, in which the CS and US come on at the same time (Figure 3.1) would produce the strongest conditioning, but Pavlov found virtually no conditioning in that arrangement. He found similarly poor results with backward conditioning, in which the US is presented before the CS. Even if the CS followed the US very closely, little conditioning occurred. If contiguous stimuli are associated, as Pavlov and the British Associationists believed, why is no association formed when a CS and a US are presented simultaneously? The answer, it now appears, is that an association is formed—it’s just that this association does not lead to the performance of a conditioned response. The clearest evidence that associations are formed when stimuli are presented simultaneously has come from research on a lie6674X_03_c03_087-114.indd 90 3/14/12 4:15 PM CHAPTER 3 Section 3.1 The Laws of Association phenomenon called sensory preconditioning. In a typical experiment, neutral stimuli such as a light and tone are presented together in an initial, preconditioning phase, and then one of these stimuli—say the light—is paired with a US such as shock. The typical result is that fear is conditioned not only to the light but also to the tone, even though the tone was not present when shock was delivered. The implication is that when the tone and light were presented together during the first phase, an association was formed between them: Tone light When the light was later paired with shock, a second association would have been formed, between the light and shock: Light shock With the light and tone previously paired, subsequent presentation of the tone activated the representation of the light in the brain, which in turn elicited fear: Light Fear Tone In most sensory preconditioning experiments, the sensory stimuli are presented sequentially in the preconditioning phase—in our example, the rats would first have heard the tone and then seen the light. In a variant of this procedure reported by Rescorla (1980b), however, the sensory stimuli—both tastes—were presented simultaneously. (The rats simply drank a water solution flavored with the two tastes.) When one of the tastes was then paired with illness, the rats developed an aversion to both tastes. One possible interpretation of this result is that it was caused by generalization: When the rats developed an aversion to one of the tastes, this aversion generalized to the other taste. However, Rescorla showed that the first taste became aversive only if the tastes had been presented together during preconditioning. This suggests that simultaneous presentation forged an association between the two tastes, and it was this association that eventually caused the aversion to be transferred from one taste to the other. But if simultaneous presentation of a CS and US can result in the formation of an association, why doesn’t it result in conditioning? One possible explanation stems from the fact that conditioning is an adaptive process whose purpose is to allow organisms to prepare for forthcoming events. In most conditioning experiments the CS precedes the US, and the CS thus allows the subject to take preparatory action. If a light is paired with a puff of air to the eye, for example, then subjects can blink before the puff arrives, thereby protecting their eye. If a light and an air puff are presented simultaneously, however, there is no time to prepare. When responding would serve no purpose, as in simultaneous and backward conditioning, no response is made. Put another way, conditioning seems to involve at least two separate stages: In the first, an association is formed between the CS and the US; lie6674X_03_c03_087-114.indd 91 3/14/12 4:15 PM Section 3.2 Contingency CHAPTER 3 in the second, presentation of the CS seems to trigger some kind of decision process that determines whether that CS will elicit a response. Simultaneous conditioning thus provides us with our first hint that conditioning might not be as simple as it appears. Frequency A second variable that the British Associationists thought determined the strength of an association between two events was the frequency of their pairing, or the number of times they occur together over a period of time. Pavlov’s research on salivary conditioning strongly supported this view (see Figure 2.3) and so has subsequent research. In general, the strength of the conditioned response seems to increase most during the early trials of conditioning, with the rate of increase gradually declining as training continues, until performance eventually reaches a stable plateau, or asymptote. Intensity The third major principle proposed by the British Associationists was that the strength of any association depends on the vividness or intensity of the stimuli involved. Associations involving emotional or traumatic events, for example, were thought to be better remembered. If someone suffered intense pain while waiting for a wound to be treated at a hospital, any future visit to that hospital would elicit vivid memories of that pain. Again, research on conditioning strongly supports this principle. Annau and Kamin (1961), for example, found that the amount of fear conditioned to a tone depends on the intensity of the shock that follows the tone (see Figure 2.11). There is also evidence that the intensity of the CS is of some importance, although this effect appears weaker (see Grice, 1968). On the whole, then, the armchair speculations of the British Associationists have been impressively confirmed by research under controlled conditions. Associative learning really does depend on contiguity, frequency, and intensity. The frequency with which one counts sheep in order to sleep may strengthen the association between sheep and sleepiness. (Presumably, this would also hold true for sheep who count people to fall asleep!) 3.2 Contingency Until the 1960s, all the available evidence converged on a coherent and satisfying picture of conditioning in which the foundation stone was contiguity: If two events are contiguous—that is, occur closely together in time—then an association will be formed between lie6674X_03_c03_087-114.indd 92 3/14/12 4:16 PM CHAPTER 3 Section 3.2 Contingency them. The strength of this association might be modulated by other factors such as the intensity of the stimuli involved. Fundamentally, though, conditioning appeared to be a simple process in which associations were automatically formed between contiguous events. In 1966, however, two landmark papers were published that posed a fundamental challenge to traditional views of the role of contiguity and unleashed an intellectual ferment—revolution would not be too strong a word—that is still continuing. The Concept of Contingency The first of these papers was the work of Robert Rescorla, then a graduate student at the University of Pennsylvania. In his paper, Rescorla sugThis rice farmer depends on heavy rainfall gested that contiguity between two events was to irrigate crops. In deciding whether to not sufficient for conditioning; something more pay for a weather forecasting service, was needed. Specifically, he suggested that a CS it would be important for the farmer must not only be contiguous with a US but must to consider not only the probability of also be an accurate predictor of the occurrence of rain when it was forecast but also the the US. To understand what he meant by this, probability when it was not forecast. let’s take a look at the following example: Suppose you were in a room where you occasionally heard a tone that lasted for two minutes. And further suppose that you also occasionally received electric shocks. (Not a pleasant example, but it will be useful for reasons that will become clear.) Figure 3.3 shows two possible variants of this situation. In situation A, a shock is always presented at some point while the tone is on, but shock is never presented in the tone’s absence. In this situation the tone is a good predictor: It warns that you that a shock is imminent. Now consider situation B. Here too, shocks occur during the tone, but shocks also occur in the absence of the tone. Indeed, the likelihood of receiving a shock is just as great in the absence of the tone as in its presence. In this situation the tone has no predictive value: When a tone is on, you are no more likely to receive a shock than when it is off, and therefore, the tone does not help you predict when you will receive a shock. lie6674X_03_c03_087-114.indd 93 The presence of dark storm clouds in the sky is often a sign that rain will soon fall; although dark clouds do not always signal rain, there is a high likelihood that if one occurs, the other will soon follow. And, equally important, when clouds are not present, rain is not likely to occur. When both of these conditions are satisfied, so that rain is much more likely in the presence of clouds than in their absence, we say that there is a high level of contingency between the two events. 3/14/12 4:16 PM CHAPTER 3 Section 3.2 Contingency Figure 3.3: CS-US contingencies CS US Perfect predictor A Random group B In this experiment, Rescorla studied the effects of the predictor between the US and the CS; he suggested that the CS must be contiguous and act as a predictor of the occurrence of the US. Although we have not shown it in this figure, it is also possible to imagine an intermediate situation in which the tone had some predictive value but the prediction was not perfect. For example, suppose the shock occurred in both the presence and absence of the tone, but was more likely when the tone was present. Clearly the tone in this situation would have some predictive value, although you wouldn’t be certain about what was going to happen. What these examples illustrate is that the predictive value of a CS can vary widely—at one extreme, a tone might be a perfect predictor of when shock will occur; at the other, it might be no help at all. It would be quite useful, therefore, if we had some way of measuring predictive value. In fact, there are several such measures, but one of the most useful is a mathematical statistic called a contingency. Because contingencies are defined in terms of probabilities, however, we need to start by quickly reviewing what we mean by a probability. A probability is just a mathematical expression of the likelihood that an event will occur. If there is no chance of an event occurring, its probability is said to be 0; if the event is certain to occur, its probability is said to be 1.0. Suppose that a tone was presented 100 times, and that every one of these presentations was followed by a shock. In that case, the probability of a shock following the tone would be 1.0. Let us further suppose that the shock never occurs in the absence of the tone. The probability of a shock in the absence of the tone would then be 0. This is the situation shown in Figure 3.3A—shock would be much more likely when the tone was on than when it was off. Now consider the situation shown in Figure 3.3B, in which shocks occurred in the absence of the tone as well as in its presence. If the probability of a shock in the absence of the tone was the same as in its presence, the tone would have no predictive value; its onset would not signal any greater probability of shock. lie6674X_03_c03_087-114.indd 94 3/14/12 4:16 PM CHAPTER 3 Section 3.2 Contingency Even though tone is followed by shock equally often in both of our examples, its predictive value would be very different. One way of capturing this idea is to say that the predictive value of a CS depends on the extent to which the probability of the US changes when the CS is present. And that is what a contingency statistic measures. The contingency between a CS and a US is defined as the difference between the probability of the US when the CS is present and when it is absent (Allan, 1980). The formula would look like this: Contingency = ( (– ( probability of US in presence of CS probability of US in absence of CS ( The greater the difference—the more the probability of the US in the presence of the CS exceeds that in its absence—the greater the contingency. You can check how well you understand the concept of contingency by considering the following hypothetical example. Suppose that you are a farmer who has just moved to a new county, and you need to be able to predict the probability of rain to decide whether to plant your corn. A salesperson for a weather forecasting company approaches you and tells you that the company has developed a new forecasting system that is far more accurate than any existing method. As proof, the salesperson shows you evidence that last year the company predicted rain on 100 days and it actually rained on 95 of those days. Should you buy the new forecasting service? The answer, from the point of view of contingency, is no—or, at least, not necessarily. To determine the value of the company’s predictions, you need to know not only the probability of rain when it was forecast, but also the probability when it was not forecast. Suppose, for example, that you had just moved to an area where it always rains on 95 days out of 100. In this case, the company’s predictions would clearly be of very little aid in deciding whether rain was imminent. To evaluate the accuracy of any forecast or prediction, in other words, you need to consider not only how often the predicted event occurs when it is predicted but also how often it occurs when it is not predicted. If these probabilities are similar, then the prediction will not help you very much. The Role of Contingency in Conditioning A subject in a classical conditioning experiment faces a problem similar to that of the farmer who wants to predict rain. Consider a rat that suddenly becomes ill. If this illness were caused by food it had eaten earlier, it would obviously be advantageous for the rat to avoid that food in the future. In searching for a cue that could predict illness, however, the rat (like the farmer) might be seriously misled if it relied solely on contiguity. Just because the rat becomes ill after eating lima beans, for example, doesn’t necessarily mean it was the lima beans that made the rat ill; if the rat becomes ill on days when it doesn’t eat lima beans as well as on days when it does, there would be no point to its avoiding lima beans in the future. In seeking to identify the true cause of an event, in other words, animals and humans would do better if they considered the contingency between two events as well as their contiguity. lie6674X_03_c03_087-114.indd 95 3/14/12 4:16 PM CHAPTER 3 Section 3.2 Contingency Rescorla, as mentioned earlier, was the first to wonder about the role of contingency. What would happen, he asked, if a tone and shock were presented contiguously, as in most fearconditioning experiments, but the shock was also presented in the absence of the tone, thereby eliminating their contingency? Although Rescorla’s initial work on contingency was published in 1966, we will look at the results of an experiment he reported in Taste is a very refined sense, as this professional coffee taster 1968. Figure 3.4 illustrates the can attest. It allows us to detect foods that may be spoiled design of this experiment. In the simply by the way they taste: for example, spoiled milk tastes random group, rats received a sour and contaminated apple juice can have a vinegary flavor. series of tones and shocks delivIt turns out that taste cues are more readily associated with ered totally at random. Subillness than visual cues. jects in the contingency group received tones whenever their counterparts in the random group did, and they also received some—but not all—of the shocks delivered to subjects in the random group. Specifically, they received the shocks given to the random group while the tone was present but not when the tone was absent. Both groups thus received the same number of tones and the same number of pairings of the tone with the shock. Figure 3.4: Rescorla’s contingency experiment of 1968 2 min tone shock Random group Contingency group In this figure a tone is indicated by a pink bar and a shock by an orange bar. An orange bar inside a pink bar indicates that the shock occurred while the tone was on. In the Random group, shocks were presented at totally random intervals, sometimes during the tone and sometimes in its absence. The Contingency group also received the shocks presented during the tone, but not those presented in its absence. lie6674X_03_c03_087-114.indd 96 3/14/12 4:16 PM Section 3.3 Preparedness CHAPTER 3 How should conditioning in the two groups compare? If conditioning depends simply on contiguity, then conditioning should be equal, because both groups had the same number of tone-shock pairings. If contingency also matters, however, we should expect conditioning only in the contingency group. In accordance with this prediction, Rescorla found powerful conditioning in the contingency group and none whatsoever in the random group. In other experiments reported in his 1968 paper, Rescorla manipulated the degree of contingency between the CS and the US and found that conditioning depended on the precise level of contingency: The greater the contingency, the stronger the conditioning. In one sense, this is hardly surprising; it is just a fancy way of saying that conditioning depends on the extent to which the CS is a good predictor of the US. 3.3 Preparedness The second seminal paper of 1966 was by Garcia and Koelling, and they also challenged the assumption that any two events that were contiguous would be associated. In particular, these researchers challenged the idea that it did not matter what stimulus was chosen as a CS. Pavlov had claimed, “Any natural phenomenon chosen at will may be converted into a conditioned stimulus . . . any visual stimulus, any desired sound, any odor, and the stimulation of any part of the skin” (1928, p. 86). Subsequent research almost universally supported Pavlov’s position—until, that is, the publication of Garcia and Koelling’s paper. Taste-Aversion Learning Their experiment had its origins in naturalistic observations of animal behavior—in particular, in observations of a phenomenon in rats called bait-shyness. Rats, it turns out, resist human efforts to exterminate them. When they encounter a novel food, they tend to take only the smallest taste at first; if it turns out to be poisoned bait but they survive, they rarely if ever touch that food again. Classical conditioning provides a possible explanation for the rats’ avoidance of the bait: Ingestion of the poisoned bait produces nausea, and this reaction becomes conditioned to the smells and tastes that precede the nausea. On future occasions, the rats avoid the bait because its odor or taste makes them ill. As we saw in Chapter 2, this phenomenon is known as tasteaversion learning. As plausible as this explanation is, it cannot account for one aspect of the rats’ behavior. lie6674X_03_c03_087-114.indd 97 If this mouse ate a piece of poisoned cheese and became ill, it would be extremely reluctant to eat the same food in the future, no matter how much cheese it was tempted with; this phenomenon is known as “taste-aversion learning.” 3/14/12 4:16 PM Section 3.3 Preparedness As part of Garcia and Koelling’s research on taste-aversion learning, rats were given flavored water to drink from a tube and then made ill. CHAPTER 3 Although the poisoned rats later avoided the bait, they showed no reluctance to return to the place where they had been poisoned to consume other foods found there. If associations form between any contiguous events, then we should expect place cues to be associated with illness as readily as taste and odor cues, but this did not appear to be happening. Was it possible that the rats could associate nausea with tastes, but not with visual cues? To test this hypothesis under controlled laboratory conditions, Garcia and Koelling allowed rats to taste distinctly flavored water from a drinking tube that was wired so that every lick produced not only water but a brief noise and light flash. Following exposure to this taste-noise-light compound, the rats received a dose of radiation sufficient to make them ill. Then, on a test trial, the rats were exposed to each of the compound stimuli separately, to determine which ones had become aversive. A lick produced either the flavored water or plain water plus the noise-light compound. As shown in Figure 3.5a, the rats were now very reluctant to drink the flavored water, but they had no such compunctions about the bright-noisy water. These naturalistic observations suggested that nausea could be conditioned to gustatory cues but not visual ones. lie6674X_03_c03_087-114.indd 98 3/14/12 4:16 PM CHAPTER 3 Section 3.3 Preparedness Water intake Figure 3.5: Water intake before and after conditioning pre-cond post-cond “bright-noisy” water Water intake a. X ray b. Electric shock pre-cond post-cond Time Water intake before (pre) and after (post) conditioning: (a) when X rays were used as the US; (b) when shock was used as the US. The green bars represent intake of the flavored water; the orange bars represent intake of plain water when licking produced a noise and light. Source: Based on Garcia & Koelling, 1966 An alternative explanation, however, was possible: Perhaps the noise and light used in the experiment were simply too faint to be detected, so conditioning would not have occurred with any US. To test this hypothesis, Garcia and Koelling repeated their experiment with the same compound CS, but with electric shock as the US instead of X rays. The results for the suppression test are shown in Figure 3.5b, which illustrates that the audiovisual stimulus produced suppression of drinking and the taste stimulus had no effect. We thus face this strange situation in which nausea cannot be conditioned to a noise, nor fear to a taste, even though each of these conditioned stimuli is easily associated with the other US. Subsequent research established that it is possible to associate taste with shock and noise with illness, but it is much more difficult, requiring many more trials (for example, Best, Best, & Henggeler, 1977). Seligman (1970) coined the term preparedness to refer to the fact that we seem prepared to associate some CS–US combinations more readily than others. lie6674X_03_c03_087-114.indd 99 3/14/12 4:16 PM Section 3.3 Preparedness CHAPTER 3 Implications Garcia and Koelling’s experiment has proved to be one of the most influential studies on learning ever published. In part, this is because their study provided the first clear evidence for the existence of taste-aversion learning, a process that plays a major role in determining food preferences. (See Chapter 2.) In addition to its practical significance, taste-aversion learning proved to have important implications for how psychologists view learning, and, indeed, for our understanding of scientific discovery. Before we complete our discussion of Garcia and Koelling’s work, therefore, we will look briefly at these implications. The Role of Contiguity in Associative Learning According to the traditional view, all that matters in conditioning is contiguity: If two events are contiguous, then they will be associated. The evidence for preparedness, however, clearly shows that this is not the case. In the taste-aversion experiment, noise was just as contiguous with illness as taste was, but this contiguity did not result in learning. Contiguity, therefore, is not sufficient for learning to take place. Other evidence has shown that contiguity is not even necessary. In the Garcia and Koelling experiment, there was a delay of at least 20 minutes between the presentation of the taste and the animals’ becoming ill; in a subsequent, memorable experiment by Etscorn and Stephens (1973), conditioning occurred despite a delay of 24 hours. Clearly, conditioning is not due simply to the linking of events that happen to occur contiguously: Some other process or processes must be involved. Garcia and Koelling’s experiment thus contributed to a major theoretical shift in the way we view conditioning— from a simple process to one of considerable sophistication and complexity. We will examine this shift in greater detail in sub- Just because two events occur together in time doesn’t mean sequent chapters. that a link will be forged between them. The Uniformity of Conditioning Pavlov, and most of the Western psychologists who followed him, viewed conditioning as an entirely general process. No matter what CS was paired with what US, the same associative process would be involved, and the principles of conditioning would thus also be the same. The principles of taste-aversion learning, however, are not the same as those of, say, salivary conditioning. As we have seen, it is easy to associate a light with food but very difficult to associate that same light with illness. Moreover, the role of contiguity is also different: In salivary conditioning, the longest CS–US interval at which conditioning will occur is on the order of minutes, whereas in taste-aversion learning it can be as long as 24 hours. And whereas salivary conditioning is a fairly slow process, requiring many trials, strong taste aversions can be learned in just one or two trials. (For a review, see Domjan, 1980.) lie6674X_03_c03_087-114.indd 100 3/14/12 4:16 PM Section 3.3 Preparedness CHAPTER 3 These differences should not be exaggerated. Regarding contiguity, for example, it is true that the longest interval at which conditioning will occur is longer in taste-aversion learning than in salivary conditioning, but shorter intervals still produce stronger conditioning (Andrews & Braveman, 1975). Nevertheless, the principles of conditioning clearly do vary for different responses, if only in degree. The Adaptive Value of Preparedness Why should this be? To answer this question, it is helpful to begin by considering why classical conditioning occurs at all. The Value of Conditioning In discussing Pavlov’s research, we referred repeatedly to his view that the process of conditioning has evolved because it helps animals survive in their natural environments. One way of thinking about conditioning is as a means of identifying stimuli that cause or predict important events: If an animal knows where food is available, for example, or which of the other animals in its vicinity is likely to attack it, then it can use this information to guide appropriate action. Culler (1938) expressed this view with some eloquence. [Without a signal] the animal would still be forced to wait in every case for the stimulus to arrive before beginning to meet it. The veil of the future would hang just before his eyes. Nature began long ago to push back the veil. Foresight proved to possess high survival-value, and conditioning is the means by which foresight is achieved. (Culler, 1938, p. 136) Salivary conditioning provides one example of the advantages of foresight: If a dog knows when food is coming, it can begin to salivate beforehand, and this will allow it to consume the food more quickly—not a small advantage when predators or other hungry dogs are around. Similarly, if a rat learns to freeze whenever it sees a predator, this freezing may enhance its chance of escaping detection and thus surviving. In a world where intense competition exists over every food source, a hyena’s ability to salivate to certain cues before food presents itself provides an adaptive advantage. lie6674X_03_c03_087-114.indd 101 In these examples, we can only speculate about the functional value of the conditioned response, but in some cases we have direct evidence. One example concerns the conditioning of sexual arousal. In an experiment by Zamble, Hadad, Mitchell, and Cutmore (1985), male rats were given access to a sexually receptive female. In one group, the female’s appearance was preceded by a signal; in the other group, it was not. When the female’s appearance 3/14/12 4:16 PM Section 3.4 Blocking CHAPTER 3 was signaled, males initiated and completed copulation more quickly. However unromantic such behavior might seem, a male that approaches a female faster is likely to have an advantage over competing suitors, and a male that finishes more quickly will have spent less time in a position in which it is highly vulnerable to attack. The conditioning of sexual arousal will give this male a significant advantage in reproducing, thus ensuring that its genes—including those responsible for the susceptibility to conditioning of sexual arousal—will be passed on to succeeding generations (Hollis, Pharr, Dumas, Britton, & Field, 1997). The Value of Preparedness The principles of taste-aversion learning seem to differ from other forms of conditioning, because these variations contribute to the species’ survival. Consider a rat that became ill after eating rancid meat. If the only learning system it possessed was an all-purpose mechanism that associated all contiguous events, then it would have developed an aversion to all the stimuli present when it became ill. In other words, the rat might have been A rat would be unlikely to associate illness with a singing bird; equally likely to develop an taste would be a more adaptive predictor of illness in this case. aversion to the sound of a drill or to the smell of flowers or perhaps to a bird that was singing nearby. If it thereafter tried to escape every time it heard a singing bird, it would be more likely to die of exhaustion than to prosper. The pressures of natural selection would thus favor rats that associated illness with preceding tastes, rather than with irrelevant lights or sounds (see also Wilcoxon, Dragoin, & Kral, 1971; Beecher, 1988). 3.4 Blocking The 1960s were a difficult time for the principle of contiguity. First, Rescorla showed that temporal contiguity between a CS and a US is not sufficient to ensure conditioning; the CS must also be a good predictor of the US. Then Garcia and Koelling showed that even valid predictors are not always conditioned. In 1969, a third event undermined still further the traditional view of contiguity and suggested an alternative analysis to replace it. This event was the publication of a paper by Leo Kamin. lie6674X_03_c03_087-114.indd 102 3/14/12 4:16 PM CHAPTER 3 Section 3.4 Blocking Kamin’s Research on Blocking Kamin (1969) gave rats fear-conditioning trials in which two stimuli, a noise (N) and a light (L), were paired with an electric shock. In a control group, the noise and the light came on together, remained on for three minutes, and were immediately followed by the shock. To assess conditioning to the light, Kamin used a conditioned emotional response (CER) test in which the light was presented while the rats pressed a bar to obtain food. The suppression ratio for the light was 0.05, indicating substantial fear conditioning. (Recall from Chapter 2 that a suppression ratio of 0.50 indicates no fear and zero indicates maximal fear.) In other words, fear was strongly conditioned to the light for the rats in the control group. Just as a hand can block the light from the sun, prior conditioning to a stimulus can block conditioning to a second conditioned stimulus that now accompanies it. blocking group control group Kamin was interested primarily in a second group, though. The subjects in this second group received the same pairings of the noise-light compound with shock, but these compound trials were preceded by trials in which the noise by itself was paired with shock. Pretraining Conditioning N NL shock NL shock shock This first phase produced substantial fear conditioning to the noise. For subjects in the blocking group, therefore, the noise already elicited fear when the compound trials began. What effect should we expect this to have on conditioning to the light? According to a contiguity analysis, fear should be conditioned to the light in both groups, because, in both, the light was repeatedly and contiguously paired with the shock. The results for the two groups, however, proved to be very different. The suppression ratio in the control group was 0.05, meaning they showed substantial fear conditioning to the light; however, the ratio for subjects in the blocking group ? those who were given preliminary conditioning to the noise ? was 0.45, a statistic only barely distinguishable from the 0.50 level representing no fear. In other words, prior conditioning to the noise had blocked conditioning to the light. Kamin called this phenomenon, in which prior conditioning to one element of a compound prevents conditioning to the other element, blocking. lie6674X_03_c03_087-114.indd 103 3/14/12 4:16 PM Section 3.4 Blocking CHAPTER 3 Surprise! To account for blocking, Kamin proposed an intriguing explanation. When an important event such as shock occurs, he said, animals search their memories to identify cues that could help to predict the event in the future. Imagine that a rat foraging for food in a forest is suddenly attacked by an owl. If the rat survives the attack, it will search its memory to identify cues that preceded the attack, helping it avoid such an event in the future. If the rat had seen the owl in a tree just before the attack, for example, then the next time it saw an owl it would dive for cover. Kamin’s first assumption, then, was that unconditioned stimuli trigger memory searches for predictive cues. His second assumption was that such searches require effort. In tasteaversion conditioning, for example, we have seen that animals may develop an aversion to foods consumed as much as 24 hours before they became ill, indicating that any memory search must cover events spread over at least this time period. Such a search would require According to Kamin’s theory, if a bird had already been considerable time and effort, conditioned to fly away when it heard a gunshot, it would and Kamin speculated that in probably not be conditioned to fly away on seeing a hunter, order to save energy, subjects if it now saw the hunter at the same time as it heard the would scan their memories gunshot; prior conditioning to the first cue (the noise) would only if the US were unexpected block conditioning to the second cue (the hunter). or surprising. If the US were expected, then by definition some cue predicting its occurrence must already have been available, so that no further search would be needed. To see how this analysis can account for blocking, consider first the control group that received only the compound trials. The first shock would have been unexpected and would have triggered a memory search for the cause. The rats would remember the preceding noise and light, and thus both cues would be associated with the shock. Similarly in the blocking group, presentation of the shock during the preliminary phase would have surprised the rats and thus triggered a memory search in which the rats recalled the noise and associated it with the shock. When the noise was then presented as part of the noise-light compound, the rats would have expected the shock to follow and hence would not have been surprised. As a result, they would not have searched their memories and thus would not have learned about the relationship between the light and the shock. According to Kamin, then, blocking occurs because the US is already expected. To test this analysis, he used an ingenious design in which he changed the US used during the compound trials so that its presentation would come as a surprise. As before, a noise was paired with shock during preconditioning, but during conditioning the shock presented lie6674X_03_c03_087-114.indd 104 3/14/12 4:16 PM CHAPTER 3 Section 3.4 Blocking at the end of each noise-light compound was unexpectedly followed by a second shock five seconds later: Noise Shock   Noise-Light Shock . . . Shock During pretraining, the rats would have learned that the noise was followed by a shock, which would have produced strong fear conditioning to the noise; on the compound trials, therefore, no conditioning to the light would have occurred, because the rats would have expected the first shock. The second shock, however, would have been a surprise. The rats should therefore search their memories for possible causes, notice the light, and associate it with the shock. And that is what Kamin found: When the light was later presented on its own, it produced powerful fear in the group that had received two shocks. To sum up, conditioning seems to depend on whether the US is surprising, as any change in a US that makes it surprising—making it more aversive or less aversive—produces conditioning. Implications Research on contingency, preparedness, and now blocking have shattered the traditional view of conditioning, which posited that contiguity between a CS and a US was sufficient for the formation of an association. Instead, conditioning seems to be concentrated on stimuli that are good predictors of a US—either because, in the evolutionary history of the species, these stimuli have proven to be valid predictors (preparedness), or because they currently provide useful information (contingency). Blocking fits the same pattern, as fear was conditioned to the stimulus that was the best predictor of the US over time— the noise that preceded every shock, rather than the light that preceded only some. (See also Wagner, Logan, Haberlandt, & Price, 1968.) Conditioning, in other words, turns out to be a beautifully adaptive system that targets the cues most likely to be the true causes or predictors of important events. We now know that conditioning is not a simple or automatic process; it involves both memory and attention. lie6674X_03_c03_087-114.indd 105 Kamin not only identified a crucial problem—how does the brain identify the best predictor of the US, if not by contiguity?—he also provided a persuasive solution. Conditioning, in his account, is not limited to cues that are physically present when a US is encountered; instead, the use of memory allows the search for predictors to be broadened to cues that occurred seconds, minutes, or—in the case of taste aversions—even hours earlier. Memory thus plays a central role in conditioning, and this realization helped to produce a fundamental shift in how psychologists viewed conditioning. It was understood now to be a far more complex process, one that also involved cognitive processes such as memory and attention. Conditioning might not be as complex as language, but neither was it as primitive as previously believed. We will discuss this shift further in Chapter 4, but 3/14/12 4:16 PM Section 3.5 Applications CHAPTER 3 if you would like to find more material dealing specifically with the role of memory in conditioning, some excellent research is available in papers by Revusky (1971), Wagner, Rudy, and Whitlow (1973), Bouton and Nelson (1998), and Manns, Clark, and Squire (2002). 3.5 Applications By studying conditioning in the highly controlled environment of the laboratory, Pavlov and his successors hoped to tease apart the complex processes involved in the formation of associations. The laboratory, though, was not an end in itself—the ultimate goal was always to apply the knowledge gained in the laboratory to helping people in real life. In this section, we will examine attempts that have been made to apply conditioning principles to such problems as phobias, cigarette smoking, and alcoholism. Phobias The first speculations about the possibility of applying classical conditioning principles to practical problems appeared in the study by Watson and Rayner (1920), discussed in Chapter 2, in which they conditioned “little Albert” to fear a rat by pairing the rat with presentations of a loud noise. At the end of their published report, they suggested that fear conditioning in children might explain many of the phobias and anxieties found in adults. If so, it might also be possible to use conditioning principles to eliminate these fears. The Origin of Phobias One way to assess the claim that adult phobias are the result of conditioning is to interview phobics about the circumstances that led to their phobias. On the whole, studies that have done this have supported the claim. In one such study, by Öst and Hugdahl (1981), 58% of those interviewed were able to recall traumatic incidents that triggered their phobias. What, though, of the 42% who could not—how did their phobias arise? In some cases the cause appeared to be vicarious learning, in which individuals learn that a stimulus is dangerous because they see someone else being injured. In one such case, a boy developed a severe dental phobia when he accompanied a friend to the dentist and the dentist’s drill accidentally punctured his friend’s cheek (Öst, 1985, cited by Barlow & Durand, 1995). At first glance vicarious learning and conditioning might appear to be alternative explanations, but vicarious learning can be understood as a kind of conditioning if we assume that animals and lie6674X_03_c03_087-114.indd 106 According to the principle of vicarious learning, we can develop a phobia not only by experiencing pain ourselves but also by witnessing others experiencing that pain. Seeing a scene like the one above might not encourage future trips to dentists. 3/14/12 4:17 PM Section 3.5 Applications CHAPTER 3 humans are innately programmed to become distressed when they see another member of their species hurt. If a young monkey sees his mother becoming frightened when she encounters a snake, for example, it would clearly be advantageous for the infant to learn to associate snakes with fear. In the course of evolution, the sight of others’ distress could thus have become an unconditioned stimulus for anxiety—indeed, the boy who saw his friend injured became so distressed that he ran from the dentist’s office. (For more direct evidence that the sight of others in distress can lead to the conditioning of fear, see Mineka & Cook, 1986, and Gerull & Rapee, 2002.) What about cases in which phobics cannot recall any traumatic incident, whether involving themselves or others? One possibility is that such incidents occurred but were forgotten. This might at first seem implausible—surely someone who experienced a trauma severe enough to produce a phobia would remember it?—but people’s memories for painful incidents are surprisingly poor. In one study cited by Loftus (1993), a survey of 1,500 people who had been hospitalized within the preceding year revealed that 25% could not recall this hospitalization! Moreover, memory seems to be particularly poor for incidents experienced when we are young, which is when many phobias develop. (See, for example, Henry, Moffitt, Caspi, Langley, & Silva, 1994.) The issue of how phobias arise is still controversial, but it does look as if a very substantial proportion of specific phobias—those involving specific stimuli such as snakes and spiders—really are due to conditioning, as Watson and Rayner had suggested. (For divergent views on this issue, see Mineka & Öhman, 2002, and Poulton & Menzies, 2002.) Systematic Desensitization What, then, of Watson and Rayner’s other claim, that if phobias are caused by conditioning then it should also be possible to use conditioning principles to overcome them? One of their suggestions was to associate the stimulus that elicited fear with a pleasurable experience such as eating or sexual stimulation. The pleasant feelings elicited by these events would be incompatible with fear, they reasoned, so that if these reactions could be conditioned, then fear might be suppressed. This is, of course, the counterconditioning procedure originally described by Pavlov. Mary Cover Jones (1897-1987) was dubbed the “mother of behavior therapy” by her colleague Joseph Wolpe due to her research on the “deconditioning” of the fear reaction; her study of a three-year-old boy named Peter who had a fear of rabbits has been referenced more extensively than any other aspect of her work. lie6674X_03_c03_087-114.indd 107 The first human application of this counterconditioning strategy was in an experiment by Mary Cover Jones (1924). One of her subjects, a boy named Peter, was terrified of rabbits, and, following Watson and Rayner’s 3/14/12 4:17 PM Section 3.5 Applications CHAPTER 3 suggestion, she resolved to introduce the rabbit while Peter was engaged in the pleasurable activity of eating. She introduced the rabbit gradually over a period of days, on the eminently reasonable assumption that simply dropping the rabbit on to Peter’s lap while he was eating would not have produced the desired effect. She kept the rabbit at a distance at first and then moved it progressively closer to the boy’s chair. The result was nothing short of spectacular, as Peter not only lost all fear of the rabbit but actively began to seek out opportunities to play with it. Despite the impressive success of this treatment, there was little further research until the mid 1950s, when Joseph Wolpe reported a therapy he had developed called systematic desensitisation (1958). Wolpe’s technique was similar to that of Jones, except that his counterconditioning procedure used relaxation rather than eating as the response. In addition, instead of actually presenting the fear stimuli, he asked his patients This Moulin Rouge cabaret dancer looks extremely comfortable with a snake to imagine them. A therapist using Wolpe’s techdraped over her shoulders; however, a nique would ask patients to describe situations person with a snake phobia, known as that frightened them and then would arrange ophidiophobia, would experience intense these stimuli in a hierarchy based on their aver- fear and possibly even panic attacks at the siveness. A patient who had a fear of snakes, for touch of a snake and would benefit from example, might find the idea of looking at a toy a counterconditioning procedure such as snake to be only somewhat threatening, while systematic desensitization. the idea of coming across a snake in the woods might be even more frightening, and the idea of picking up a live snake perhaps the most frightening situation of all. These images involving snakes would then be arranged in a hierarchy of ascending order according to their ability to produce fear or anxiety. The therapist would also train the patient in special techniques to encourage deep relaxation (see Wolpe & Lazarus, 1966). Typically, a patient would start with the lowest stimulus in the hierarchy (the one that produced the least amount of fear) and try to relax while visualizing that scene. Only when the patient reported complete relaxation while imagining that scene would the therapist ask the patient to visualize the next scene, and so on. Wolpe reported remarkable success in eliminating phobias with this technique, and subsequent studies have largely confirmed his claims. In a study by Paul (1969), for example, students who had severe anxieties about public speaking were treated with either systematic desensitization or insight-oriented psychotherapy (which focuses on identifying the cause of the phobia). When examined two years later, 85% of those given desensitization showed significant improvement relative to pre-treatment levels, compared with 50% in the psychotherapy group and only 22% in an untreated control group. The effectiveness of systematic desensitization varies depending on the phobia being treated, but it is one of the most effective treatments currently available for phobias involving specific objects such as snakes or blood, or activities such as flying (Borden, 1992; Thyer & Birsinger, 1994). lie6674X_03_c03_087-114.indd 108 3/14/12 4:17 PM CHAPTER 3 Section 3.5 Applications Exposure Therapy Exposure therapy has sometimes been used to treat individuals who are afraid to fly; the procedure might begin by showing the client pictures of airplanes and gradually increasing his exposure, until eventually he is able to fly with little or no anxiety. One limitation to the effectiveness of systematic desensitization is that the conditioned stimulus is imagined rather than experienced directly. In some cases, patients have overcome their fear of an imagined stimulus such as a snake only to find themselves still fearful when they encountered a snake in real life. To overcome this problem, many therapists now use exposure therapy, in which patients are exposed to the actual stimuli that frighten them. As in systematic desensitization, exposure is gradual, starting with situations that elicit minimal fear and advancing only gradually to more frightening situations. Patients are still encouraged to relax, but this element of the treatment typically receives less emphasis because of the difficulties of remaining fully relaxed while engaged in physical activities such as moving toward a snake. Exposure is thus closer to straightforward extinction, in contrast to systematic desensitization’s emphasis on counterconditioning, but it too has proven very effective (for example, Öst, Stridh, & Wolf, 1998; Barlow, Raffa, & Cohen, 2002). Aversion Therapy A second major application of conditioning principles has been aversion therapy, in which the goal is not to eliminate fear but rather to harness it to produce avoidance of a harmful situation. This principle is by no means new, with some of the most imaginative—and gruesome—applications stemming from ancient times. Pliny the Elder, for example, recommended a treatment for alcoholism that consisted of covertly putting the putrid body of a dead spider in the bottom of the alcoholic’s tankard. When the drinker would innocently tip the contents into his mouth, the resulting revulsion and nausea supposedly would deter him from ever drinking again. A somewhat more modern example (technically, at any rate) involved the treatment of a 14-year-old boy who wanted to give up smoking (Raymond, 1964). The boy was given injections of apomorphine, a drug that produces intense nausea, and each injection was timed so that it would take effect while the boy was in the middle of smoking. Here’s an excerpt from Raymond’s study: lie6674X_03_c03_087-114.indd 109 Pliny the Elder (23 AD–79 AD) was a Roman naturalist and natural philosopher who wrote Naturalis Historia, an encyclopedic work that collected much of the knowledge of his time. 3/14/12 4:17 PM 3.5 Applications CHAPTER 3 On the first occasion he was given an injection of apomorphine 1/20g, and after seven minutes he was told to start smoking. At eleven minutes he became nauseated and vomited copiously. Four days later he came for the second treatment, and said that he still had the craving for cigarettes, but had not in fact smoked since the previous session because he felt nauseated when he tried to light one. . . .Two months later he left school and started working. He said he had “got a bit down” at work and wanted to “keep in with the others,” so he had accepted a proffered cigarette. He immediately felt faint and hot, and was unable to smoke. It is now a year since his treatment, and his parents confirm that he no longer smokes. (Raymond, 1964, p. 290) Although Raymond’s results were highly impressive, early attempts to apply his procedures to problems such as smoking and alcoholism were less successful. In retrospect, the main problem in these early studies was probably the unconditioned stimulus used. Raymond used apomorphine, which was seen to be very effective; however, because apomorphine is a dangerous drug that requires medical supervision, many of the early follow-up studies used electric shock instead. As we saw in our discussion of preparedness, stimuli such as the taste of alcohol or the odor of cigarette smoke are difficult to associate with shock, and this could account for the higher failure rate in the studies that followed Raymond’s initial research (Lamon, Wilson, & Leaf, 1977). Once research on taste-aversion learning in rats made this problem clear, researchers switched to USs that would be easier to associate. For alcoholism, nausea-inducing drugs such as Antabuse are now used. A further problem in the early studies was that even where treatment was effective initially, patients often relapsed when treatment was discontinued. The cause was probably discrimination learning, as patients would have rapidly learned that whereas drinking alcohol in the clinical setting was followed by illness, drinking in the neighborhood bar or with friends had no such consequences. Rather than learning not to drink, they simply learned not to drink in the presence of the experimenter! More recent studies have therefore incorporated other forms of training to help patients cope with temptation once treatment has ceased. One approach has been to provide counseling during treatment to teach strategies for coping with the urge to smoke or drink when it arises. Another approach has been to provide posttreatment “booster” sessions to help maintain the aversion established during treatment. In one study using this approach, Boland, Mellor, and Revusky (1978) paired alcohol with lithium during treatment and arranged additional conditioning trials after patients had been discharged. When they assessed their patients six months after discharge, they found that 50% of the chronic alcoholics in the treatment group were still abstinent, compared with only 12% of the controls. The use of multicomponent treatments in which aversion therapy has been combined with other approaches has contributed to an improvement in the long-term effectiveness of aversion therapy (Hall, Rugg, Tunstall, & Jones, 1984; O’Farrell et al., 1996). In a review, Elkins (1991) reported that approximately 60% of alcoholics treated with aversion therapy were still abstinent one year after treatment, an impressive result for a problem that is notoriously difficult to treat. However, this does not mean that aversion therapy is always appropriate. The need for hospitalization means that aversion therapy for alcoholism is expensive, and its unpleasant nature leads to higher drop-out rates during treatment. Where milder forms of treatment are possible, therefore, they are preferred. For patients suffering from chronic alcoholism, however, aversion therapy appears to be an effective alternative. lie6674X_03_c03_087-114.indd 110 3/14/12 4:17 PM Review Questions CHAPTER 3 Summary and Review • • • • • • • Until the mid 1960s, psychologists believed that conditioning was a fundamentally simple process in which an association is formed whenever two stimuli are presented together. (As shown by sensory preconditioning, it is not necessary that one of these stimuli be a US—any salient stimuli that occur together may become associated.) The strength of the association was determined by the contiguity of the stimuli, their intensity, and the frequency of their pairing. The first major challenge to this belief came from Rescorla’s research on contingency: Contiguous pairings of a tone with shock did not result in conditioning if the shock also occurred in the absence of the tone. An experiment by Garcia and Koelling also showed that contiguous pairings of a CS with a US does not necessarily result in conditioning—the outcome depends on which CS is paired with which US. Rats will readily associate illness with a taste, but not with a noise or light. Both animals and humans seem prepared to form some CS–US associations more easily than others, a predisposition that probably reflects an evolutionary history in which some stimuli proved to be more likely causes of illness than others. Kamin provided a third demonstration that contiguous pairings do not always produce conditioning. He paired a noise-light compound with shock and found that no fear was conditioned to the light if the noise had previously been paired with shock—conditioning fear to one element of a compound blocked conditioning to the other element. Kamin’s explanation was that when we encounter a US, we search our memories to identify possible predictors, but because this search is effortful, we search only when necessary. Specifically, we search only if we are surprised by the US—if we expected it, then an adequate predictor must have already been available. Together, these results provided convincing evidence that conditioning is not simply a matter of associating stimuli that occur together. Even in the simplest conditioning situations, learning seems to depend on cognitive processes such as memory and attention. Fears are often acquired through conditioning, and psychologists have used conditioning principles to eliminate these fears. Exposure therapy and systematic desensitization have both proven highly effective. Conditioning principles have also been used to treat alcoholism, by pairing the taste of alcohol with illness. Aversion therapy has been effective when administered in hospitals, but other techniques are sometimes needed to ensure that this aversion is maintained once patients return to their normal lives. Review Questions 1. Why did simultaneous and backward conditioning seem to pose problems for the principle of contiguity? How can these apparent anomalies be explained? 2. How did Rescorla disentangle the roles of contiguity and contingency in conditioning? 3. How did Garcia and Koelling show that the conditioning of a stronger aversion to a taste than to a light was not simply the result of greater salience of the taste as a conditioned stimulus? lie6674X_03_c03_087-114.indd 111 3/14/12 4:17 PM Concept Check CHAPTER 3 4. How might classical conditioning contribute to an animal’s survival? Why might it be better not to associate a US with all the stimuli that precede it? 5. How did Kamin account for blocking? 6. Is contiguity necessary or sufficient for conditioning? What is the relevant evidence? 7. How could the Pavlovian concepts of generalization and counterconditioning be used to account for the success of systematic desensitization? 8. Can conditioning principles account for the development of phobias? Concept Check 1. Food is presented for three seconds, followed by a two-second tone. This is an example of a. b. c. d. simultaneous conditioning. delay conditioning. trace conditioning. backward conditioning. 2. The contingency between a CS and a US is determined by a. b. c. d. the time between the beginning of the CS and the beginning of the US. the probability of the US. the number of pairings of the CS and the US. the probability of the US in the presence of the CS and in the absence of the CS. 3. Research on taste-aversion learning suggests that contiguity is ____ for classical conditioning. a. b. c. d. necessary sufficient necessary and sufficient neither necessary nor sufficient 4. To explain blocking, Kamin proposed that a. b. c. d. all salient stimuli elicit memory searches. only unexpected stimuli elicit memory searches. all salient stimuli elicit attention. only unexpected stimuli elicit attention. 5. Exposure therapy is potentially a better treatment for phobias than systematic desensitization because a. b. c. d. it requires fewer trials. it involves real rather than imagined stimuli. it allows more scope for relaxation. all of the above Answers: 1) c, 2) d, 3) d, 4) b, 5) b lie6674X_03_c03_087-114.indd 112 3/14/12 4:17 PM Key Terms CHAPTER 3 Key Terms asymptote In mathematics, a stable value that a curve on a graph approaches but never quite reaches. As used in learning, it generally describes the level of performance at which improvement ceases, so that further training would produce no additional improvement. aversion therapy A procedure for eliminating a behavior by conditioning fear to stimuli associated with the performance of that behavior. backward conditioning A procedure in which first a US is presented, then a CS. blocking A phenomenon in which prior conditioning to one element of a compound prevents conditioning to other elements. contiguity Literally, proximity or closeness. In learning, the principle of contiguity says that the formation of an association between two events depends on their closeness in time. A stronger version is that contiguity is both necessary for the formation of an association (the events must be contiguous to be associated) and sufficient (any events that are contiguous will be associated). contingency A measure of the extent to which two events occur together, or covary, over time. A contingency coefficient is a mathematical statistic determined by two probabilities—the probability that a US will occur in the presence of a CS, and the probability that it will occur in the absence of the CS. If a US is more likely to occur in the presence of a CS than in its absence, we say that there is a contingency between them. lie6674X_03_c03_087-114.indd 113 delay conditioning A procedure in which a CS is presented and then continues until a US is presented. (In some experiments the CS terminates when the US starts; in others, the two overlap.) Some definitions further restrict this term, confining it to situations in which there is also a long interval between CS onset and US onset. exposure therapy A treatment for phobias in which phobics are exposed to phobic stimuli and given an opportunity to learn that these stimuli are no longer followed by traumatic events (extinction). Exposure starts with stimuli that elicit low levels of fear and gradually progresses to more frightening situations. frequency The number of times an event occurs. In classical conditioning, the strength of conditioning depends on how often a CS is paired with a US. intensity In classical conditioning, this usually refers to the strength of a stimulus— for example, how bright a light is. Conditioning is stronger when the US is intense. preparedness The tendency to associate some CS–US combinations more readily than others. Other terms for this phenomenon include relevance, selective association, and associative bias. sensory preconditioning A procedure in which two neutral stimuli are presented together and subsequently one of them is paired with an unconditioned stimulus. The typical result is that responding is conditioned not only to the conditioned stimulus but also to the stimulus that was paired with it during the first phase. 3/14/12 4:17 PM Key Terms CHAPTER 3 simultaneous conditioning A procedure in which a CS and a US are presented at the same time. trace conditioning A procedure in which a CS is presented but then terminated before presentation of the US. systematic desensitization A therapy for phobias based on counterconditioning. Patients visualize fear-evoking stimuli while relaxing, to associate the stimuli with relaxation instead of fear. vicarious learning The acquisition of new behaviors arising from observation of others’ experiences. In vicarious conditioning, conditioning occurs to a CS as a result of seeing someone else receive pairings of that CS with a US. lie6674X_03_c03_087-114.indd 114 3/14/12 4:17 PM 4 Theories of Conditioning Learning Objectives After reading this chapter, you should be able to do the following: • Describe the Rescorla-Wagner model and how the authors translated Kamin’s cognitive account of conditioning into a more associative account based on a mathematical equation. • Understand how mathematical models work, and how they can be used to explain known phenomena such as conditioning, extinction, and blocking. • Predict new mathematical models, such as the overexpectation effect. • Identify challenges to the model from phenomena such as latent inhibition and configural learning, and how the model could be modified to account for them. • Differentiate between Pavlov’s substitution theory and Tolman’s concept of expectation and describe some of the experimental research that supports each. • Define and explore the two-system hypothesis, which proposes that both views were correct, as two different learning systems emerged in the course of evolution. • Explain the role of awareness in conditioning and the related form of learning called “causal learning.” • Examine the seemingly more sophisticated form of learning called causal learning, and the possibility that it might be based on the same associative processes that underlie conditioning. lie6674X_04_c04_115-152.indd 115 4/9/12 8:18 AM Section 4.1 The Rescorla-Wagner Model CHAPTER 4 The phenomenon of classical conditioning is basically very simple: If a CS and a US are repeatedly presented together, the CS will eventually begin to elicit the same response as the US does by itself. Pavlov proposed an equally simple theory to account for this evidence, namely that whenever two centers in the brain are active simultaneously, the connection between them will be strengthened. In essence, all that matters is contiguity: If a CS and a US occur together in time, they will be associated. This account is delightfully simple, and until the 1960s it was used to explain virtually all the known facts about conditioning. Research on contingency, preparedness, and blocking, however, posed a fundamental challenge to the notion that simple contiguity is sufficient. In the case of contingency, for example, Rescorla showed that conditioning would not occur if a US was equally likely to occur in the absence of a CS as in its presence. The fact that a CS and US occur together, in other words, does not guarantee conditioning, and thus conditioning must involve more than simply linking brain centers that are active simultaneously. In this chapter we will consider what this “more” might be and examine current theories about what really happens when a CS and a US occur together. We will see that although Pavlov was not totally wrong, conditioning involves a much more intricate web of processes than a simple contiguity explanation suggests. 4.1 The Rescorla-Wagner Model Recall from Chapter 2 the idea that in order for conditioning to occur, the CS must be an accurate predictor of the occurrence of the US (contingency). In fact, Rescorla’s research revealed that animals are remarkably sensitive to the probability of the US both in the presence of the CS and in its absence. The obvious way to account for this sensitivity is to assume that animals are somehow capable of computing probabilities. If rats sometimes receive shocks in the presence of a tone and sometimes in its absence, for example, they might count how many shocks occur while the tone is present and also assess how much time has elapsed. Using this data, they could determine the average probability of the shock in the presence of the tone and, in a similar fashion, compute the shock’s probability in the tone’s absence. Finally, they could compare the two probabilities to determine whether the tone signals an increase in the likelihood of shock. It is possible that animals do carry out the complex processes implicit in this account— measuring time, counting events, and computing probabilities.—but many consider it unlikely. In 1972, however, two psychologists published a theory that offered a much simpler account. Robert Rescorla and Allan Wagner, from Yale University, offered an account for almost every major aspect of conditioning—the occurrence of conditioning itself, extinction, blocking, the effects of contingency, and so on. And they achieved all this using only a single, simple equation! The Rescorla-Wagner model has proved to be one of the most remarkable and influential models in psychology, and we therefore will begin our exploration of theories of conditioning by examining it in some detail. Before we begin, it might be worth noting that some of the following sections are difficult and may require careful rereading. This might seem to contradict the previous claim that the model is simple, but once you understand lie6674X_04_c04_115-152.indd 116 3/14/12 4:21 PM Section 4.1 The Rescorla-Wagner Model CHAPTER 4 it, you’ll see that it really does involve only a few simple assumptions. Because the model is stated in mathematical form, you may have to master unfamiliar symbols and concepts before it all begins to make sense. Mastering this new terminology may not be easy, but the potential reward is an insight into how a few simple assumptions can explain what seems to be a bewildering array of unrelated facts. The Importance of Surprise One powerful impetus for the Rescorla-Wagner model came from Kamin’s work on blocking. As we saw in Chapter 3, Kamin found that when a noise-light compound was followed by shock, no fear was conditioned to the light if fear had previously been conditioned to the noise. From the perspective of contiguity, this result was bewildering: Why, when the light was paired with an electric shock, was fear not conditioned to it, regardless of the noise? If you became ill several hours after eating peanut butter, you might wonder if it had been the cause, but if this continued to happen every time you ate it, your belief that it was the cause would strengthen, until eventually you were certain. Kamin’s explanation was that when we encounter an important event, we search our memories to identify stimuli that might have caused or predicted it—if we know that a shock is coming, we at least have the possibility of preparing for it. However, this kind of memory search uses scarce cognitive resources that might be needed for other purposes—an animal may need to stay vigilant, for instance, for the appearance of a possible predator. So Kamin assumed that memory searches occur only if the US is a surprise. In the example of the noise-light compound, the rats had already learned that noise was a predictive cue for shock and thus would not have been surprised by the shock when it was associated with both the noise and the light. They would not have needed to search their memories again for a predictor and thus would not have learned about the relationship between the light and the shock. In sum, Kamin’s theory thus proposed that whether or not conditioning will occur depends crucially on whether the occurrence of the US surprises us. To see how Rescorla and Wagner built on this idea, let’s suppose a painful rash suddenly appears on your face. It would be useful to be able to predict this type of event, so let’s imagine that when the rash first appears, you search your memory for possible causes. You remember having eaten a peanut butter and jelly sandwich earlier in the day. Could that have caused the rash? You would become even more suspicious if another rash appeared after you ate some peanut butter cups. At that point you might have felt that peanut butter was the cause, but because you loved peanut butter, you were reluctant to accept this. So a few days later you ate something else that contained peanut butter, and the rash returned. lie6674X_04_c04_115-152.indd 117 3/14/12 4:21 PM Section 4.1 The Rescorla-Wagner Model CHAPTER 4 Figure 4.1 plots how your expectation that eating peanut butter was the cause of your rash might have changed with experience. At first you would have no expectation that it would cause a rash, but after each new experience your expectation would have become stronger, until eventually you were certain. Figure 4.1: Rescorla-Wagner model and conditioning The expectation that peanut butter causes a rash would become stronger each time you ate peanut butter and then developed a rash. We have assumed that expectations increase rapidly at first but then more slowly, and the likely reason for this is surprise. The first time you noticed the rash, it would have come as a complete surprise, and when you remembered eating the peanut butter, you would have formed a tentative belief that it was the cause. The next time you ate peanut butter, therefore, you would have been half-expecting illness to follow. When it did, you would not have been nearly so surprised, and as a result you would not have needed to alter your expectation as much. If an expectation is completely wrong, it makes sense to modify it substantially, but the more accurate the expectation is, the less we need to adjust it. As your expectation of a rash increased over trials, therefore, you would have needed to modify it less and less each time, until eventually your initially-tentative expectation hardened into certainty. This intuition—that how much we adjust our expectations depends on how surprised we are—was Rescorla and Wagner’s fundamental insight. Where Kamin had suggested that surprise determines whether conditioning occurs, Rescorla and Wagner now proposed that surprise also determines how much conditioning occurs: The greater the surprise, the greater the conditioning. For example, the first time you received a jolt of static electricity when you touched a metal door knob in your house, there would be a substantial increase in your fear of touching that knob. The hundredth time you approached the door, however, you would already have a high level of anxiety, and yet another shock would be unlikely to produce much of an increase. lie6674X_04_c04_115-152.indd 118 3/14/12 4:21 PM Section 4.1 The Rescorla-Wagner Model CHAPTER 4 However, Rescorla and Wagner wanted to avoid mentalistic explanations of the kind we have been developing here. We have no way of knowing what a rat is thinking, and, as we saw in Chapter 1, there can also be problems in inferring the thoughts and emotions of humans. Rescorla and Wagner therefore wanted to express their ideas in more neutral terminology. When a CS is paired with a US, they said, an association or connection will be formed between them; they didn’t speculate about what thoughts or feelings might accompany this association. A Mathematical Model Because they wanted to be able to predict the amount of conditioning that took place, they made a second change to Kamin’s theory: They expressed their ideas in mathematical form. This can make their model appear intimidating, so as we discuss their model in more detail, hold onto the fact that underlying the equations is really a simple idea—how much conditioning occurs each time we encounter a US depends simply on how much we are surprised by it. In the early history of psychology, mentalists used introspection to try to understand the mind. This led to many theories about the mind’s structure, although introspection didn’t provide the kind of clear evidence needed to say which ones were correct. The Learning Curve As we have seen, Rescorla and Wagner assumed that when a CS and US occur together an association will be formed. They used the symbol V to represent the strength of this association. They further assumed that if these CS–US pairings were repeated (recall our discussion of frequency in Chapter 3), the strength of the association would increase in roughly the manner shown in Figure 4.2a. As you can see by looking at the top graph, the more pairings, or trials, that occur for a particular CS and US, the stronger their association becomes. However, it becomes clear after looking at Figure 4.2b that this increase in associative strength is not constant over trials. On the first trial, V increases by a substantial amount. Over successive trials, the increase in V on each trial gets progressively smaller, until eventually V approaches a stable value. lie6674X_04_c04_115-152.indd 119 3/14/12 4:21 PM CHAPTER 4 Section 4.1 The Rescorla-Wagner Model Figure 4.2: Increases in associative strength according to Rescorla-Wagner model 1.0 0 1 2 3 4 5 6 7 8 9 1.0 0 1 2 3 4 5 6 7 8 9 Associative strength (V) increases over number of conditioning trails (n) according to the Rescorla-Wagner model. Figure 4.2a shows a typical learning curve; Figure 4.2b shows the same curve, indicating the change in associative strength on each trial (∆V) and the asymptotic value of associative strength (Vmax). lie6674X_04_c04_115-152.indd 120 4/9/12 8:19 AM CHAPTER 4 Section 4.1 The Rescorla-Wagner Model Rescorla and Wagner used the symbol ∆V to represent the change in associative strength on each trial (∆, or delta, is the mathematical symbol for change). The change in associative strength produced by the first trial was ∆V1, the change on trial 2 was ∆V2, and so on. As we saw in Chapter 3, a stable value that a curve approaches but never quite reaches is called an asymptote, and we will use the symbol Vmax to represent the asymptotic value of V (Figure 4.2b). Quantifying Surprise We can summarize the model to this point by saying that associative strength increases over trials until it reaches a stable maximum value; in mathematical terms, V increases by ∆V on each trial until it approaches Vmax. For example, if we wanted to condition fear to the sound of a tone and we decided to do this by pairing tone with shock, the associative strength between them would As one can see by looking at the image above, the two ties in a set of railroad tracks increase rapidly during the first few pairings, or trials. As the pairings continued, the strength of will run next to each other but never meet. the conditioning would continue to increase, but In geometry, an asymptote is a line that a curve approaches but never quite reaches; the amount of increase—how much fear increased there is always a gap between the two. on any given trial—would be smaller each time. Eventually, each new increase would be so small that for all practical purposes fear would have reached a maximum level and would not increase any further. (For the purposes of strict accuracy it would be more accurate to say that fear would approach this asymptotic level but would never quite reach it.) At this point, further pairings would not produce any significant increase in fear. If we want to predict how much conditioning will occur, then, we need a formula to predict ∆V. A number of formulas were possible; in choosing one, Rescorla and Wagner were guided by their assumption that the amount of conditioning depends on the amount of surprise. To quantify surprise, they focused on the relationship between V and Vmax. At the beginning of conditioning, when associative strength is low, we are not expecting the US and so will be surprised when it occurs. When associative strength is high, on the other hand, we will be expecting the US and hence are less surprised when it occurs. So, when associative strength is low (and thus when V is far below its maximum value), we are very surprised; when associative strength is high (and thus when V is close to Vmax), we are much less surprised. The difference between V and Vmax, therefore, provides us with a useful index of surprise: The closer V is to Vmax, the less we are surprised when the US is presented. Figure 4.3 illustrates this point by focusing on two trials, one that occurs early on in the conditioning process and one that occurs late. lie6674X_04_c04_115-152.indd 121 3/14/12 4:21 PM CHAPTER 4 Section 4.1 The Rescorla-Wagner Model Figure 4.3: Quantifying surprise based on the relationship between V and Vmax V This figure shows the relationship between V and Vmax early and late in conditioning. Early in conditioning (point 1), the difference between V and Vmax is great, and so surprise is strong. Later (point 2), the difference is much less, and thus surprise is much lower. Early in conditioning (point 1), there will be a large difference between V and Vmax, and substantial conditioning will occur. As conditioning proceeds, however (point 2), the difference between V and Vmax will become smaller, and the occurrence of the US will occasion less surprise. So, how surprised we are depends on how far V is from Vmax. Another way of saying this is that surprise depends on how different the value of V is from the value of Vmax: The greater the difference in their values, the more we are surprised. Putting all of these ideas together, the notion that the amount of conditioning depends on the amount of surprise can potentially be translated into mathematical form by saying that the amount of conditioning on any trial n (∆Vn) will depend on the difference between V and Vmax: ∆Vn ≈ Vmax − Vn where Vn = the strength of the association at the beginning of trial n ∆Vn = the change in the strength of the association produced by trial n lie6674X_04_c04_115-152.indd 122 3/14/12 4:21 PM Section 4.1 The Rescorla-Wagner Model CHAPTER 4 Parameters In our presentation of the model to this point, we have talked as if the learning curve shown in Figures 4.2 and 4.3 is found in all conditioning curves, but this is not quite true. The overall shape of the curve—increasing over trials, but at a declining rate—is indeed uniform, or at least roughly so, but the asymptotic level of conditioning can vary, and so too can the speed of conditioning. In discussing taste-aversion learning, for example, we noted that such aversions develop very quickly, whereas salivary conditioning generally requires many trials for conditioning to reach its peak. To allow the model to account for variations in the speed of conditioning, Rescorla and Wagner added a constant, c, to their equation. The complete statement of the equation was thus: ∆Vn = c(Vmax − Vn) In mathematics, a constant in an equation is called a parameter. Suppose, for example, that a person’s weight was always 20 times as great as their height. If we used the symbol H to represent height and W to represent weight, then we could express this relationship with the following equation: W = 20H If a woman was 5 feet tall, her weight would be 100 pounds; if she was 6 feet tall, her weight would be 120 pounds, and so on. The values for height and weight would thus vary, but the value of 20 would always be the same. It would be a constant, and in mathematics any constant in an equation is called a parameter. If we use a linear equation such as weight = 2 × height to predict a boy’s weight, “2” is the constant value, or parameter, in the equation. Simply plugging in a value for “height” and multiplying this value by a constant of 2 will give us a value for “weight.” The Rescorla-Wagner equation actually has two parameters: c and Vmax. Vmax determines the asymptotic level of conditioning, the level attained after many pairings. If a tone is paired with a 100-volt shock, for example, the asymptotic level of fear is much greater than if the shock is only 20 volts. Knowing this, Rescorla and Wagner specified that the value of Vmax depends on the intensity of the US—the value of Vmax used in the equation is greater when a 100-volt shock is used than when the shock is 20 volts. The other parameter in the Rescorla-Wagner model, c, determines the speed of conditioning—the greater the value of c, the larger will be the change in associative strength on each trial. Thus, the faster conditioning will reach its asymptote more quickly as the value of c increases. If you come across a statement of the model in journal articles, you might not recognize it, as the symbols Rescorla and Wagner used to represent these parameters are not the same as the ones used here; we’ve altered the symbols to make the model easier to follow. And lie6674X_04_c04_115-152.indd 123 3/14/12 4:21 PM Section 4.2 The Rescorla-Wagner Model: Evaluation CHAPTER 4 one final note—should you want to play with the model to see what it might predict in different situations, note that the value of Vmax depends on what US is used, especially its intensity, and the value of c depends on both the CS and the US and must be between 0 and 1. Note that the value of c in our version of the equation must lie between 0 and 1. 4.2 The Rescorla-Wagner Model: Evaluation We now have an equation with which we can predict the precise change in associative strength on any trial. To test the model, it might seem that all we need to do is present a series of CS–US trials, calculate the predicted value of V for each trial, and see if our predictions are correct. However, to calculate the model’s predictions for learning on any trial, we need to know what values of c and Vmax to use. Suppose, for example, that we ran a salivary conditioning experiment in which a light (CS) was paired with 20 grams of food (US); what values of c and Vmax should we use in order to predict the outcome? One solution would be to run a pilot experiment using 20 grams of food, see what values of c and Vmax produce the most accurate prediction, and then use these values in future experiments. If we found that setting Vmax at 7 produced accurate predictions when the US is 20 grams of food, for example, then we could then use this value in any further applications involving this US. When a theory has several parameters, however, this process turns out to be considerably more complex than it sounds, and in the entire history of learning theory there has only been one sustained effort to estimate parameters in this A “pilot study” is a small-scale, preliminary study that is way (Hull, 1943). When this often conducted prior to a larger study in order to test design effort failed, after more than a parameters, assess feasibility, and address other practical decade of effort, it convinced matters related to the research. many conditioning theorists that mathematical models were more trouble than they were worth. Given this history, Rescorla and Wagner decided not to try to determine the appropriate values for c and Vmax; instead, they used totally arbitrary values! The use of arbitrary values might seem pointless, because the model will generate different quantitative predictions—for example, how many drops of saliva to expect—depending on which values are used. And as we have no way of knowing which of these values might be correct, we have no way of deciding which prediction to believe. The model’s quantitative predictions are thus of no value, but it turns out that the model can still make some interesting qualitative predictions. For example, suppose that a dog received lie6674X_04_c04_115-152.indd 124 3/14/12 4:21 PM Section 4.2 The Rescorla-Wagner Model: Evaluation CHAPTER 4 pairings of a tone with food. We could not predict how many drops of saliva would be observed, but regardless of what values we used for c and Vmax, the model would always predict that salivation would increase as training continued. So, although we could not predict the number of drops of saliva, we could still make qualitative predictions about whether salivation would increase or decrease. This might still seem a waste of time—we hardly need a sophisticated mathematical model to tell us that conditioning will increase over trials—but Rescorla and Wagner were able to show that even simple statements of this kind can lead to interesting and unexpected predictions. Explaining the Old To see how this can happen, we will first consider how the model accounts for relatively straightforward phenomena such as conditioning and extinction. Then, once the basic operations of the model are a bit clearer, we will turn to some of its more striking predictions. To begin, though, let us take a look at how the model accounts for the basic shape of the learning curve during conditioning. Conditioning Suppose that we repeatedly paired a tone with food, as in the hypothetical experiment whose results are illustrated by the learning curve presented in Figure 4.2. To see what sort of results the model might predict in this situation, let us arbitrarily assume that the values of c and Vmax are as follows: c = 0.30 Vmax = 1.0 Although the rise and fall of the tides may change the exact location of a shoreline, its basic curve is always the same. In a similar way, although the values of c and Vmax vary depending on the type of conditioning experiment being conducted, the predicted shape of the learning curve remains the same. If so, how much learning should we expect? At the beginning of trial 1, associative strength would be zero, because the CS has never been paired with the US before. The amount of conditioning on that trial would therefore be: ∆V = c (Vmax − V1) = 0.30 (1.0 − 0) = 0.30 (1.0) = 0.30 At the beginning of trial 2, the strength of the association would thus be 0.30: Trial 1 started with a strength of zero, and its strength was then increased (∆V1) by 0.30, giving a new strength of 0.30. The change in associative strength produced by the second trial would then be: lie6674X_04_c04_115-152.indd 125 3/14/12 4:21 PM Section 4.2 The Rescorla-Wagner Model: Evaluation CHAPTER 4 ∆V2 = c (Vmax − V2) = 0.30 (1.0 − 0.30) = 0.30 (.70) = 0.21 Since the associative strength of V at the beginning of trial 2 (V2) was 0.30, and it was increased by 0.21 on that trial, the value of V at the beginning of trial 3 would be: V3 = V2 + ∆V2 = 0.30 + 0.21 = 0.51 The predicted values for V for the first four trials are shown in Table 4.1. As you can see, they correspond to the values plotted in Figure 4.2. Table 4.1: Using the Rescorla-Wagner Model to Predict Conditioning Trial Vn 𝚫Vn = c (Vmax − Vn) 1 0.00 ∆V1 = 0.30 (1 − 0.00) = 0.30 2 0.30 ∆V2 = 0.30 (1 − 0.30) = 0.21 3 0.51 ∆V3 = 0.30 (1 − 0.51) = 0.15 4 0.66 ∆V4 = 0.30 (1 − 0.66) = 0.10 Our success in predicting these hypothetical data is perhaps not too surprising (especially when you consider that the calculations were done first and the graph simply plots these calculations!), but it does indicate the capacity of the model to generate learning curves of the shape found in most conditioning experiments. The predicted shape of the curve is the same, moreover, regardless of what values of c and Vmax are used. These parameters alter the height of the asymptote and the speed with which it is reached, but in all cases the basic shape of the curve remains the same. (You might find it useful to verify this for yourself by working through some calculations using other values. You can use any value for Vmax, but the value of c must lie between 0 and 1.0.) Extinction What about other aspects of conditioning? For example, can the model explain decreases in responding as well as increases? Yes, and it does so using exactly the same equation used to predict conditioning. The key to understanding how one equation can predict diametrically opposite results lies in Vmax. We have said that Vmax is the strength of the association that would be produced if a CS and US were paired repeatedly. In extinction, we know that the level of conditioning reached after extended training is zero (in other words, there is no longer an association between the CS and the US). The value of Vmax on any trial in which a US is not presented, therefore, must also be zero. To see the implications of this, suppose that after the third conditioning trial in our previous example we began to present the CS by itself. On the first extinction trial, V would have an initial value of 0.66 (see Table 4.1), but as a result of nonreinforcement on that trial, its associative strength would be changed by lie6674X_04_c04_115-152.indd 126 3/14/12 4:21 PM CHAPTER 4 Section 4.2 The Rescorla-Wagner Model: Evaluation ∆V1 = c (Vmax − V1) = 0.30 (0 − 0.66) = 0.30 (−0.66) = −0.198 The strength of the association, in other words, would be decreased by approximately 0.20, and its new strength would be V2 = 0.66 – 0.20 = 0.46 Each extinction trial would decrease associative strength further, until eventually V would approach its asymptotic value of zero. Using only a single equation, therefore, the model can predict extinction as well as conditioning. Blocking We can also use the model to explain blocking. Before doing so, however, we need to consider how conditioning is affected if two stimuli instead of just one are present on a trial. We said earlier that conditioning on any trial depends on how surprising the US is, which in turn depends on how much the subject expected the US to occur. Rescorla and Wagner assumed that if two conditioned stimuli, a and b, were presented together, the subject would take both stimuli into account in estimating the likelihood of the US. Specifically, they proposed that the association or expectation at the beginning of a trial would be the sum of the strengths of each of the stimuli present...
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