Module 4: Respondent Conditioning

Module Overview

We begin our coverage of models of learning by discussing respondent conditioning, based on the work of Ivan Pavlov. In this form of learning an association is formed between two events — the presentation of a neutral stimulus (NS) and the presentation of an unconditioned stimulus (US). As you will see, though the response to the US appears similar to the response to the NS, they are not identical and in some cases the response is much different or even opposite. We will talk about more complicated forms of conditioning such as higher order conditioning and how conditioning can be appetitive or aversive, or excitatory or inhibitory. Four variations of the normal respondent conditioning paradigm will be described, centered on when in time the US and NS occur. These include delay, trace, simultaneous, and backward conditioning. We will then discuss properties governing respondent conditioning to include extinction, spontaneous recovery, generalization, and discrimination. Sensory preconditioning, latent inhibition, overshadowing, blocking, and occasion setting will be discussed and the effect they have on how easily conditioning occurs. Finally, we will discuss five theories of conditioning.

Module Outline

• 4.1. The Nuts and Bolts of Respondent Conditioning
• 4.2. Properties Governing Respondent Conditioning
• 4.3. Theories of Conditioning

Module Learning Outcomes

• Describe how respondent conditioning occurs in humans and animals.
• Outline and explain properties related to respondent conditioning.
• Describe theories related to respondent conditioning.

4.1. The Nuts and Bolts of Respondent Conditioning

Section Learning Objectives

• Describe Pavlov’s accidental discovery.
• Define respondent conditioning.
• Recognize other terms used for respondent conditioning.
• Outline the three phases of respondent conditioning. Define all terms.
• Describe and exemplify higher order conditioning.
• Contrast appetitive and aversive conditioning.
• Contrast excitatory and inhibitory conditioning.
• Outline and describe the four temporal presentations of US and NS in respondent conditioning.
• Describe the phenomena of pseudoconditioning.

4.1.1. Pavlov and His Dogs

You have likely heard about Pavlov and his dogs but what you may not know is that this was a discovery made accidentally. Ivan Petrovich Pavlov (1849-1936; 1927), a Russian physiologist, was interested in studying digestive processes in dogs in response to being fed meat powder. What he discovered was the dogs would salivate even before the meat powder was presented. They would salivate at the sound of a bell, footsteps in the hall, a tuning fork, or the presence of a lab assistant. Pavlov realized there were some stimuli that automatically elicited responses (such as salivating to meat powder) and those that had to be paired with these automatic associations for the animal or person to respond to it (such as salivating to a bell). Armed with this stunning revelation, Pavlov spent the rest of his career investigating the learning phenomenon and won a Nobel Prize in 1904 for his work.

The important thing to understand is that not all behaviors occur due to reinforcement and punishment as operant conditioning says. In the case of respondent conditioning, antecedent stimuli exert complete and automatic control over some behaviors. We saw this in the case of reflexes. When a doctor strikes your knee with that little hammer it extends out automatically. You do not have to do anything but watch. Babies will root for a food source if the mother’s breast is placed near their mouth. If a nipple is placed in their mouth, they will also automatically suck, as per the sucking reflex. Humans have several of these reflexes, though not as many as other animals, due to our more complicated nervous system.

4.1.2. Respondent Conditioning Described

Respondent conditioning occurs when we link or pair a previously neutral stimulus with a stimulus that is unlearned or inborn, called an unconditioned stimulus. Note that this form of learning also goes by the name classical conditioning or Pavlovian conditioning in honor of Ivan Pavlov.

Respondent conditioning is best described as occurring in three phases: pre-conditioning, conditioning, and post-conditioning. See Figure 4.1 for an overview of Pavlov’s classic experiment.

Let’s define terms first. The term conditioning means learning. So pre-conditioning is before learning occurs, conditioning is during learning or the acquisition of the relationship between the two stimuli, and post-conditioning is after learning has occurred. If we say something is un-conditioned it is not learned. Going back to our earlier philosophical discussion, this is learning that is innate or present at birth. Also keep in mind that the stimulus is what is sensed in the world through vision, hearing, smell, taste, or touch. The response is the behavior that is made. Making sure you have the terms straight will help you to understand respondent conditioning easier.

4.1.2.1. Pre-conditioning. Notice that pre-conditioning has both an A and a B panel. All this stage of learning signifies is that some knowledge is already present. In Panel A, the taste of food makes a dog salivate. This does not need to be trained and is the relationship of an unconditioned stimulus (US) yielding an unconditioned response (UR). The association occurs naturally. In Panel B, we see that a neutral stimulus (NS) yields nothing. Dogs do not enter the world knowing to respond to the ringing of a bell (which it hears).

4.1.2.2. Conditioning. Conditioning is when learning occurs. Through a pairing of a neutral stimulus and an unconditioned stimulus (bell and food, respectively) the dog will learn that the bell ringing (NS) signals food coming (US) and salivate (UR). The key is that the NS is presented just before the US which yields a UR (in most cases; more on that in a bit).

4.1.2.3. Post-conditioning. Post-conditioning, or after learning has occurred, establishes a new and not naturally occurring relationship of a conditioned stimulus (CS; previously the NS) and conditioned response (CR; the same response). So, the dog now reliably salivates at the sound of the bell because he expects that food will follow, and it does. If it doesn’t, the response ends or extinguishes as you will see later.

Figure 4.1. Pavlov’s Classic Experiment

Let’s now clearly define our terms:

• Unconditioned stimulus — The stimulus that naturally elicits a response.
• Unconditioned response —The response that occurs naturally when the US is present.
• Neutral stimulus — A stimulus that causes no response.
• Conditioned stimulus — The initially neutral stimulus that has been associated with a naturally occurring stimulus to bring about a response.
• Conditioned response — The response which is elicited by a CS, though it is not the same as the UR. This response is usually weaker than the UR (the dog salivates to the bell, though it does not do it as much as it does to the sight/smell/taste of the food).

Note to Student: Be sure you not only understand these terms but the acronyms used to represent them. I will use the shorthand the rest of the way through this module and in other places in the book.

To fully understand respondent conditioning, know that the pairings of an NS and US each represent a single trial, called the conditioning trial. The period between conditioning trials is called the intertrial interval. The period between the presentation of the NS and then the US (Panel C) within a conditioning trial is called the interstimulus interval.

The entire process of conditioning, to include when we first make the association between an NS and US to its strengthening over time through repeated pairings, is called acquisition. It is likely not surprising to learn that conditioning occurs quicker if the US is more intense. We will be more motivated to learn to associate making an incorrect response with shock if we receive 150 volts compared to 25 volts.

Conditioning is also more effective when the trials are spaced rather than massed (Menzel et al., 2001). For instance, spacing the trials 5 minutes apart is more effective than spacing them 25 seconds apart. One explanation for this is that we have time to rehearse the CS and US in memory during the intertrial interval and if a new trial occurs too soon, it could interfere with rehearsal (Wagner, Rudy, & Whitlow, 1973).

And we can determine how good the learning is if we toss in a test trial occasionally in which the NS is presented alone to see if it elicits the response (UR/CR; ring the bell alone and see if salivation occurs). We can also wait to see if after the presentation of the NS (bell) and before the US appears (sight of food) if the UR/CR appears on its own (salivation). In other words, does the response occur during the interstimulus interval?

4.1.3. Conditioning and its Different Forms

It is worth noting that the conditioning procedure described in the preceding section on Pavlov is not the only form it can take. In this section, we will discuss a type of layered conditioning, conditioning based on the event being something we desire or want to avoid, conditioning based on the presentation or removal of the US, and finally temporal factors that can produce unique conditioning procedures.

4.1.3.1. Higher order conditioning. Sometimes, a stimulus that is associated with a CS (formerly the NS) becomes a CS itself and elicits the CR. We call this higher order conditioning, and each level of conditioning is referred to as first, second, third, etc. order conditioning. So how might this work?

Being assaulted (US) will elicit fear (UR). A person wearing a ski mask would alone not cause any response (it is an NS1). If though, you pair the person wearing the ski mask (NS1) with the assault (US) which causes fear (UR), then the sight of a person wearing a ski mask (CS1) will elicit fear (CR). Keep in mind that with the stimuli, you see a person wearing a ski mask and feel the effects of the assault (touch or pain receptors in the skin will be activated). This is first-order conditioning (not to be confused with the training of First Order stormtroopers in Star Wars) and in this example involves a person being associated with fear.

But what if the assault occurred in an alley in your neighborhood? Now the alley (NS2) is paired with the person wearing the ski mask (CS1) which causes fear (CR), and post-conditioning shows that the alley (CS2) causes fear (CR). This is second-order conditioning and involves a location being associated with fear.

Could the time of day be a factor too? What if the mugging occurred at night? If night (NS3) is paired with the alley (CS2) which causes fear (CR), then being outside at night (CS3) could lead to fear (or at least some anxiety; CR). This would be third-order conditioning and now involves a time of day being associated with fear.

Fear was originally elicited by being assaulted. Through higher order conditioning, it was also elicited by the sight of a ski mask, being in an alley, and being outside at night. The fear reaction becomes weaker across the conditioning of these additional NS, such that our response to being outside at night could be better classified as anxiety and not so much the bona fide fear felt while being assaulted (and likely for a time afterward) which suggests that the response is strongest to the US and becomes weaker across CS1, CS2, and CS3.

4.1.3.2. Appetitive and aversive conditioning. Recall from Section 2.1.3 that appetitive stimuli are those that an organism desires and seeks out while aversive stimuli are readily avoided. In respondent conditioning, the US could be an appetitive or aversive stimulus. For instance, in appetitive conditioning, the US would be something desirable such as candy which makes us happy. Other examples could include water, food, sex, or drugs. In aversive conditioning, the stimulus is not pleasant and could include extreme temperatures, a painful sting such as from a wasp or a bite from a dog, electric shock, or something that does not smell nice. It would not be surprising to learn that conditioning occurs relatively fast when aversive US are involved. Since these stimuli could harm or kill us, learning to avoid them is adaptive and aids our survival.

4.1.3.3. Excitatory and inhibitory conditioning. Our discussion so far has included examples in which the NS is associated with the presentation of the US, called excitatory conditioning. For Palov’s dogs, they associated the ringing of a bell (NS) with the presentation of the food (US) which caused their salivation (UR). Eventually, salivation (CR) occurred to just the ringing of the bell (CS).

Interestingly enough, the absence of the US could be associated with an NS too, in a process called inhibitory conditioning. Go back to our example for higher conditioning. A person wearing a ski mask is an excitatory CS for fear but seeing someone wearing such a mask during the daytime leads to an inhibition of fear. It being day indicates a safe interval and we will not be overly concerned about ski masks. We have only ever been assaulted at night. The excitatory CS is expressed as CS+ and the inhibitory CS as CS-.

4.1.3.4. Temporal factors affecting conditioning. In the previous section we saw that generally, the US is presented after the NS though the NS could be followed by the absence of an US. These examples have also always presented the NS before the US, but this is not necessary in all cases.

First, delay conditioning involves the presentation of the NS before the US, but the NS overlaps with the US for a short period of time. In the case of Pavlov’s experiment, the bell would ring for say 10 seconds, then the food would enter the room, and then the bell would end 5 seconds after this. The ISI (interstimulus interval) should be relatively brief to use this procedure.

What if we present the NS well ahead of the US in time? Let’s say we ring the bell for 10 seconds and then there is a 5-second gap before the food enters the room. The NS and US do not overlap. This is the basis of trace conditioning and the trace is a memory that we have to access. The organism will need to remember that the NS occurred before the US to make the association, or that the bell rang before the food came in. The period of time between the NS terminating and the US beginning is called the trace interval and ideally should be short, or a few seconds.

The NS and US could occur at the same time such as in simultaneous conditioning. As you might expect, conditioning in this procedure is poor since the NS does not predict the occurrence of the US. They occur simultaneously. The bell would ring as the food enters the room. The bell-ringing does not lead to an expectation that food will come shortly, which aids with learning the association.

Finally, the US could come before the NS in a procedure called backward conditioning. The US would occur first and last for a few seconds with the NS starting near the end of this time. Hence, the NS and US co-occur for a short period of time. Of the four methods, backward conditioning is the least effective for excitatory conditioning though it could lead to inhibitory conditioning. Consider a shock paradigm in which a rat is given a shock (US) and then near the end of the shock a light is turned on (NS). The light (NS) would signal the end of the shock (US) and serve as a safety signal. Hence, the NS would become a CS-.

4.1.4. How Do You Know if Learning Occurred?

A cardinal feature of science is to verify that any change in your variable of interest (the DV) is caused by the treatment or manipulation (the IV). It could be that the elicited response was not actually caused by the NS/CS and so a product of learning or conditioning, but was caused by sensitization instead, called pseudoconditioning.

Let’s say you were working with turtles and presented them with a tone (the NS) followed by tapping on the shell (US) which resulted in the turtles withdrawing into their shells (UR). With a few such pairings, the tone (CS) would lead to withdrawing into shells (CR). So the tone has been associated with tapping, right? Possibly, but let’s say in addition to the tone we also flash a light. The turtles also withdraw into their shells at the presentation of this stimulus. In the case of sensitization, repeated presentation of a stimulus leads to an increase in how strong the response is. It can also lead to other stimuli eliciting the same response as in the case of the bright light and tone both eliciting the withdraw into shell response.

To know if the effect on the behavior you are seeing is due to conditioning and not sensitization, a simple adjustment can be made — the inclusion of a control group. The experimental group would have the tone and tap paired together resulting in a withdrawal response. The control group would have the tone played and then the tap made far apart in time. Now when the tone is presented to each group alone, the experimental group would have a strong withdrawal into shell response while the control group may have the same response, but it would be weak. The intensity of the response, or in this case it being stronger in the experimental rather than control condition, indicates conditioning has truly occurred. There is no pseudoconditioning in other words.

4.2. Properties Governing Respondent Conditioning

Section Learning Objectives

• Define extinction.
• Describe spontaneous recovery in relation to extinction.
• Differentiate stimulus generalization and discrimination.
• Describe sensory preconditioning.
• Describe latent inhibition.
• Define overshadowing.
• Define blocking.
• Explain the use of occasion setters.

4.2.1. Extinction and Spontaneous Recovery

Once an association between the NS and US has been established resulting in the NS becoming a CS, is there a way to break this association? The answer is yes, and respondent extinction involves the CS no longer being paired with the US leading to no response when the CS is presented again. For instance, the sound of a bell ringing (CS) is not followed by food (US) as the animal has come to expect and predict, and so eventually the dog stops salivating (the CR) when the bell sounds.

This property leads us to wonder if the broken association of the CS and US is permanent. The answer is no and eventually, the bell will ring making the dog salivate. If no food comes, the behavior will not continue. The organism may make the response a few more times with the strength of the response weakening each time until eventually it ends. If food comes, the salivation response will be re-established. This property is called spontaneous recovery and is when the CS elicits the CR after extinction has occurred. The association between CS and US is re-established relatively quickly once the pairing is made again.

4.2.2. Stimulus Generalization and Discrimination

When a number of similar CS or a broad range of CS elicit the same CR, stimulus generalization is said to have occurred. An example is the sound of a whistle eliciting salivation the same as the sound of a bell, both detected via audition. As you would expect, the more similar the new stimulus is to the original CS, the stronger the response will be. If a child was conditioned to be afraid of white rats, we would expect the response to be stronger if made in the presence of a white mouse rather than a German shepherd.

When the CR is elicited by a single CS or a narrow range of CSs, stimulus discrimination is said to have occurred. Teaching the dog to not respond to the whistle but only to the bell, and just that type of bell, is an example. Other bells would not be followed by food, eventually leading to the extinction of the erroneous association. Teaching an organism to make such discriminations is called discrimination training.

4.2.3. Sensory Preconditioning

There are situations in which a stimulus becomes a CS, making other stimuli it was paired with likely candidates to become a CS in the future too. This is called sensory preconditioning. Years ago, I worked for the National Institutes of Health where I did learning and memory experiments on rats and mice. Though when I started the rats in particular did not scare me, one fateful March day I injected a rat in the wrong spot, hurt it (unintentionally, of course), and it promptly turned around and took a piece of my hand with it. The bite of course elicits fear in keeping with a US-UR relationship, and for me the rat was an NS. Through that experience, and some close calls after that, I came to associate rats (CS) with fear (CR) when injecting them. Before all this, I associated rats (NS1) with their home cage where they lived (NS2) from which I took them out to handle. After the bite, I became afraid (CR) of handling rats when injecting them again (CS1), and when handling them in the home cages (CS2). Animals can detect fear, so this was not a good development, but also my confidence declined.

What was the end result? After a few months, I no longer worked with rats. This was not because of the bite incident. In keeping with what we learned about extinction above, eventually having numerous attempts injecting rats and not being bitten, the fear would have extinguished. That is what happened. Unfortunately, when the rat bit me he intensified my allergies that I did not realize were to the rats and mice I worked with. I believed they were just normal seasonal allergies and worse that year than past years, which did happen from time-to-time. I went about my business, ignorant of just how close to going into anaphylactic shock I truly was. So exit mice and rats. Enter fruit flies as my research subject of choice for learning and memory experiments from that point forward. I did that for about a year and finally had enough.

4.2.4. Latent Inhibition

The property of latent inhibition states that it is easier to condition a novel stimulus than a familiar one (Lublow, 1973). If you are using music as an NS, use a song you are unfamiliar with (or your subjects are) such as a Barry Manilow song, rather than one they know and listen to often such as Lady Gaga or Taylor Swift. So in your experiment, the song (NS) is followed by food (US) which elicits salivation (UR) in the person (much like one of Pavlov’s dogs). If you use that Taylor Swift song as the NS, salivation is not likely to occur, assuming the participants have heard it numerous times already. If you use the Barry Manilow song (CS), they will likely make the salivary response as expected (CR). The benefit of latent inhibition is that we do not form associations between CRs and repetitive stimuli in our environment that are linked by mistake or coincidentally.

Complementary to latent inhibition is the concept of US preexposure effect or exposure to a US before conditioning occurs which can make subsequent conditioning more difficult (Randich & LoLordo, 1979). Hence, the more preexposure an organism has to a US, the worse learning is later and habituation may be the culprit here. Being exposed repeatedly to the US before conditioning, the organism may habituate to it at least to some degree, making conditioning more difficult.

4.2.5. Overshadowing and Blocking

There are times when we are presented with two or more stimuli simultaneously, called a compound stimulus. We might, for instance, be presented with a light and a sound at the same time. In what is called overshadowing (Pavlov, 1927), two neutral stimuli are presented at the same time and the more salient of the two becomes a CS. Let’s say a green light and high-pitched tone were both presented at the same time and paired with the US of food which elicits salivation (UR). Which part of the compound would become the CS and elicit salivation? It appears the tone which was high-pitched would stand out more than a mere green light. But what if this green light was neon green or flashing and the tone was relatively faint and monotone? Now the light would be the more relevant or salient stimulus and become conditioned as the CS. The more salient part of the compound stimulus causes the less salient part to elicit little to no response, or remain as an NS.

In blocking (Kamin, 1969; 1968), the compound stimulus is composed of an NS and a CS and the established CS interferes with learning a new CS relationship. This differs from overshadowing which has two NS as part of the compound stimulus differing only in terms of salience. Let’s use the example above. Say you presented a dog with a tone (NS) and food (US) leading to salivation (UR). The dog will learn that when it hears the tone (CS) food is coming and will salivate (CR). What if now you present the tone (CS) with a green light several times (NS; note that the tone and light are a compound stimulus and presented simultaneously) and pair them with food (US), which causes salivation (UR). By doing this, you are trying to teach the dog to salivate to the green light, but when the stimuli are presented separately, the tone (CS) elicits salivation (CR) while the green light (NS) causes no response. The former learning has blocked the new learning.

4.2.6. Occasion Setting

The context in which learning occurs is also important. Occasion setters are stimuli that help an organism determine if the CS will be followed by a US leading to the CR. In other words, the CS elicits a CR only when the feature is present, called a feature-positive occasion setter. This feature may also indicate when a CS will not be followed by the US, called a feature-negative occasion setter (Palmatier, 2014). Consider the example of a bell (NS) being followed by food (US), which elicits salivation (UR). What if the food only comes out if the bell rings when a white light over it turns on (OS or occasion setter). If the light is on (OS) when the bell rings (NS), food comes out (US), leading to salivation (UR). If the light is off when the bell rings (NS), no food comes out, which will not elicit the behavior of salivation. We can test whether the discrimination was made by turning the light on (OS) when the bell rings (CS), which leads to salivation (CR; and the correct response) and then not having the light on when the bell rings, which should cause no response in the organism. If this is true, conditioning and the discrimination was learned. The animal now knows that food will only come out when the light is turned on during the ringing of the bell and salivate.

4.3. Theories of Conditioning

Section Learning Objectives

• Describe Pavlov’s stimulus substitution theory.
• Describe the preparatory-response theory.
• Describe the compensatory response theory.
• Describe the Rescorla-Wagner model.
• Describe Mackintosh’s attentional model.

In this final section of Module 4, we will cover five theories of conditioning that identify the processes that underly respondent conditioning. They include the stimulus substitution theory, preparatory-response theory, compensatory response theory, Rescorla-Wagner model, and the attentional model.

4.3.1. Stimulus Substitution Theory

According to Pavlov (1927), respondent conditioning is a matter of substituting one stimulus with another, or the CS acts as a substitute for the US. A connection or association is established in the brain between CS and US, and when the CS is activated alone, following acquisition, it automatically activates the US portion of the cortex. The CR, therefore, is identical or nearly identical to the UR since the connection between US and UR is hardwired or innate.

As such, the presentation of food (US) to a dog activates the food center in the cerebral cortex. This, in turn, activates the salivation center in the brain which leads to the behavior of salivation (UR). Then if we introduce an NS such as a bell ringing, it activates an area of the brain responsible for processing the sound and then is followed by an US and UR as described above. This happens over a few trials (the conditioning phase). Learning has occurred if after the presentation of the bell (CS) the area of the brain which processes the sound of the bell activates the area responsible for processing the food, which activates the area responsible for salivation, and then salivation (CR) occurs. It is the simultaneous activation of the brain areas responsible for the CS and then the US that causes a new functional neural pathway to form between the active areas.

It should be noted that Pavlov was incorrect and the process is more complex than he made it seem. Timberlake and Grant (1975) tested Pavlov’s theory by conditioning rats to expect a food pellet after a brief interval across two situations differing in terms of what type of CS was utilized. In one situation, a woodblock was secured to a platform and was the CS for food, while in the other situation a live rat was secured to the platform and was the CS for food. Utilizing the stimulus substitution theory, they predicted that the rats would approach and bite the CSs that were paired with the food. The results showed that rats in the woodblock condition bit the block CS as predicted but this did not occur when a live rat was the CS. Instead, rats groomed the live rat CS. They concluded that the nature of the CS influenced the topography of the CR, contradicting the stimulus substitution theory. The specific response that was displayed was related to the form the CS took.

Recall that in the stimulus substitution theory, the CR is identical or almost identical to the UR. We know that is not always the case though. Consider a man who has panic attacks (US) which can be quite fear-evoking (UR). Flying is an NS which yields no response. If the man is flying on a plane (NS) and has a panic attack (US) which causes him a fear (UR), then in the future the mere thought of flying in a plane (CS) will cause not fear necessarily, but definitely anxiety (CR). Hence, in this example, the CR is not the same as the UR, and not even close. Fear and anxiety are different physiological and emotional reactions. Hence, the UR and CR being identical, or even close, is not always the case as Pavlov’s theory suggests.

4.3.2. Preparatory-Response Theory

It might be that the CR exists to prepare the organism for the presentation of the US such that a dog salivates (CR) when it hears the bell ring (CS) to prepare for the arrival of the food (US). This is called the preparatory-response theory (Kimble, 1967; 1961) and it makes up for the shortcoming of the stimulus substitution theory in terms of the UR and CR not having to be identical (or close). In the example just given, the CR and UR are virtually the same. But consider a rat that is shocked (US) and displays fear (UR). If a light (NS) signals the presentation of the shock (US) causing fear (UR), then the rat will display a freeze behavior (CR) when the light turns on (CS) as it expects the shock to follow.

4.3.3. Compensatory Response Model

Not only can the UR and CR be different, the CR can be the direct opposite of the UR. In the compensatory-response model, and building off the opponent-process theory of emotion (Solomon & Corbit, 1974), a CS that has come to be repeatedly associated with the a-process or primary response to a US will with time, elicit a compensatory response or b-process. Evidence for this process comes from Siegel (1972) who gave rats repeated injections of insulin which reduces the level of glucose in the blood. He tested the CR by giving the rats an injection of saline in place of insulin. The results showed that a strong CR did occur, but it was the opposite of the reaction to insulin. The rats showed an increase in blood glucose levels (hyperglycemia CR). The CR and UR were not the same and the CR was compensatory.

Consider drug tolerance. Morphine, as a US, causes the UR of analgesia, or a reduced sensitivity to pain. Siegel et al. (1978) found that the CR to stimuli paired with morphine such as lights or tones, is hyperalgesia, or an increased sensitivity to pain. In the study, Siegel placed a rat’s paw on a hot plate and measured latency in terms of how long it took the rat to pull its paw off the plate. He found that rats injected with morphine took longer to remove their paws compared to rats which did not receive the injection. The rats which had a stimulus such as a tone paired with morphine removed their paws quicker than rats that had a stimulus not paired with morphine (the US).

4.3.4. Rescorla-Wagner Model

Robert Rescorla and Allan Wagner (1972) developed an associative model of respondent conditioning built on the idea that a given US can only support so much conditioning and must be spread out among the CSs that are present. Four main ideas are captured in this model.

1. There is a maximum associative strength that can develop between a US and CS. This is determined by the US and different US support varying maximum levels of conditioning. Stronger stimuli, therefore, support more conditioning such that if a US is a favorite food such as chicken, it will produce more salivation in an organism than a less preferred food such as Brussel sprouts.
2. Associative strength goes up with each trial, though the amount of associative strength gained on a trial is a function of the level of prior training. In general, more associative strength is gained in early trials.
3. Associative strength will accumulate quickly to some stimuli and slowly to others and some USs will produce rapid learning compared to others.
4. A specific US can only support a certain degree of conditioning even when paired with more than one stimulus. The addition of each stimulus beyond the first means that the US must share associative strength across all stimuli. Let’s say a US has 15 maximum associative strength units. If 11 of these units are distributed to Stimulus A, then only 4 can be shared with a Stimulus B. This would be particularly true in the case of a compound stimulus. A would obviously be more salient than B, or recall from earlier, A overshadows B.

The Rescorla-Wagner model also does a good job explaining blocking. Recall our earlier example of a dog presented with a tone (NS) and food (US) leading to salivation (UR). Acquisition is complete when the tone (CS) causes salivation (CR). The US of food has a maximum associative strength of 8 units which is transferred in full to the tone (CS) upon acquisition. If we now introduce an NS of a green light presented simultaneously with the tone (CS) to form a compound stimulus followed by food (US) which causes salivation (UR), then when the tone and green light are tested separately, the tone will cause salivation as it has the associative strength of 8 units assigned to it and the light will cause no response since no associative strength is left to be assigned to it.

4.3.5. Mackintosh’s Attentional Model

Nicholas Mackintosh (1975) presented a very simple theory of conditioning centered on the concept of attention. The attentional model states that how much attention an organism will give a CS is dependent on how well the CS predicts the US. If it is a good predictor, we will pay attention to the CS. If it is not a good predictor, our attention will decline. When attention is high, learning will be high as well. Organisms will pay more attention to the best predictor of the US and less attention to weaker predictors during conditioning. The theory explains blocking by saying that though the US was able to bring about learning to both the light and the tone, the animal paid less attention to the green light than it did to the tone.

Module Recap

With the conclusion of this module, you should have a firm understanding of respondent conditioning in place. You will use this knowledge to discuss applications of respondent conditioning in Module 5 and then see how the learning paradigm relates to operant conditioning, a second associative model. We will then discuss observational learning, and through an exercise you will see how the three models of learning are complementary to one another, and not competing. I hope you enjoyed this module and its coverage of respondent conditioning. If something was not clear, please ask your instructor about it.

2nd edition