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It specifies the amount of learning that will occur on a single pairing of a conditioning stimulus CS with an unconditioned stimulus US. The above equation is solved repeatedly to predict the course of learning over many such trials.
In this model the degree of learning is measured by how well the CS predicts the US, which is given by the "associative strength" of the CS. How the equation predicts various experimental results is explained in following sections. For further details, see the main article on the model.
Before a CS is conditioned it has an associative strength of zero. This increase is determined by the nature of the US e. On the first pairing of the CS and US, this difference is large and the associative strength of the CS takes a big step up. As CS-US pairings accumulate, the US becomes more predictable, and the increase in associative strength on each trial becomes smaller and smaller. Finally, the difference between the associative strength of the CS plus any that may accrue to other stimuli and the maximum strength reaches zero.
That is, the US is fully predicted, the associative strength of the CS stops growing, and conditioning is complete. R—W model: extinction[ edit ] Comparing the associate strength by R-W model in Learning The associative process described by the R—W model also accounts for extinction see "procedures" above. The extinction procedure starts with a positive associative strength of the CS, which means that the CS predicts that the US will occur.
On an extinction trial the US fails to occur after the CS. However, if that same CS is presented without the US but accompanied by a well-established conditioned inhibitor CI , that is, a stimulus that predicts the absence of a US in R-W terms, a stimulus with a negative associate strength then R-W predicts that the CS will not undergo extinction its V will not decrease in size.
R—W model: blocking[ edit ] Main article: Blocking effect The most important and novel contribution of the R—W model is its assumption that the conditioning of a CS depends not just on that CS alone, and its relationship to the US, but also on all other stimuli present in the conditioning situation.
In particular, the model states that the US is predicted by the sum of the associative strengths of all stimuli present in the conditioning situation. Learning is controlled by the difference between this total associative strength and the strength supported by the US.
When this sum of strengths reaches a maximum set by the US, conditioning ends as just described. In blocking see "phenomena" above , CS1 is paired with a US until conditioning is complete. Then on additional conditioning trials a second stimulus CS2 appears together with CS1, and both are followed by the US. Theoretical issues and alternatives to the Rescorla—Wagner model[ edit ] One of the main reasons for the importance of the R—W model is that it is relatively simple and makes clear predictions.
Tests of these predictions have led to a number of important new findings and a considerably increased understanding of conditioning. Some new information has supported the theory, but much has not, and it is generally agreed that the theory is, at best, too simple.
However, no single model seems to account for all the phenomena that experiments have produced. A number of experimental findings indicate that more is learned than this. Among these are two phenomena described earlier in this article Latent inhibition: If a subject is repeatedly exposed to the CS before conditioning starts, then conditioning takes longer.
The R—W model cannot explain this because preexposure leaves the strength of the CS unchanged at zero. Recovery of responding after extinction: It appears that something remains after extinction has reduced associative strength to zero because several procedures cause responding to reappear without further conditioning. In fact, changes in attention to the CS are at the heart of two prominent theories that try to cope with experimental results that give the R—W model difficulty.
In one of these, proposed by Nicholas Mackintosh ,  the speed of conditioning depends on the amount of attention devoted to the CS, and this amount of attention depends in turn on how well the CS predicts the US.
Pearce and Hall proposed a related model based on a different attentional principle  Both models have been extensively tested, and neither explains all the experimental results. Consequently, various authors have attempted hybrid models that combine the two attentional processes.
Pearce and Hall in integrated their attentional ideas and even suggested the possibility of incorporating the Rescorla-Wagner equation into an integrated model. However, for example, the room in which conditioning takes place also "predicts" that the US may occur. Still, the room predicts with much less certainty than does the experimental CS itself, because the room is also there between experimental trials, when the US is absent.
The associative strength of context stimuli can be entered into the Rescorla-Wagner equation, and they play an important role in the comparator and computational theories outlined below. However, as students know all too well, performance in a test situation is not always a good measure of what has been learned.
As for conditioning, there is evidence that subjects in a blocking experiment do learn something about the "blocked" CS, but fail to show this learning because of the way that they are usually tested. In particular, they look at all the stimuli that are present during testing and at how the associations acquired by these stimuli may interact.
At the time of the test, these associations are compared, and a response to the CS occurs only if the CS-US association is stronger than the context-US association. This means that the CS elicits a strong CR. Blocking and other more subtle phenomena can also be explained by comparator theories, though, again, they cannot explain everything. Most theories use associations between stimuli to take care of these predictions.
As noted above, this makes it hard for the model to account for a number of experimental results. More flexibility is provided by assuming that a stimulus is internally represented by a collection of elements, each of which may change from one associative state to another. For example, the similarity of one stimulus to another may be represented by saying that the two stimuli share elements in common.
These shared elements help to account for stimulus generalization and other phenomena that may depend upon generalization. Also, different elements within the same set may have different associations, and their activations and associations may change at different times and at different rates. This allows element-based models to handle some otherwise inexplicable results.
The time of presentation of various stimuli, the state of their elements, and the interactions between the elements, all determine the course of associative processes and the behaviors observed during conditioning experiments. To begin with, the model assumes that the CS and US are each represented by a large group of elements. When a stimulus first appears, some of its elements jump from inactivity I to primary activity A1. From the A1 state they gradually decay to A2, and finally back to I.
Element activity can only change in this way; in particular, elements in A2 cannot go directly back to A1. If the elements of both the CS and the US are in the A1 state at the same time, an association is learned between the two stimuli.
However, US elements activated indirectly in this way only get boosted to the A2 state. This can be thought of the CS arousing a memory of the US, which will not be as strong as the real thing. In consequence, learning slows down and approaches a limit. The model can explain the findings that are accounted for by the Rescorla-Wagner model and a number of additional findings as well.
For example, unlike most other models, SOP takes time into account. Many other more subtle phenomena are explained as well. Such models make contact with a current explosion of research on neural networks , artificial intelligence and machine learning. Applications[ edit ] Neural basis of learning and memory[ edit ] Pavlov proposed that conditioning involved a connection between brain centers for conditioned and unconditioned stimuli.
His physiological account of conditioning has been abandoned, but classical conditioning continues to be used to study the neural structures and functions that underlie learning and memory. Forms of classical conditioning that are used for this purpose include, among others, fear conditioning , eyeblink conditioning , and the foot contraction conditioning of Hermissenda crassicornis , a sea-slug.
Both fear and eyeblink conditioning involve a neutral stimulus, frequently a tone, becoming paired with an unconditioned stimulus. In the case of eyeblink conditioning, the US is an air-puff, while in fear conditioning the US is threatening or aversive such as a foot shock. It appears that other regions of the brain, including the hippocampus, amygdala, and prefrontal cortex, contribute to the conditioning process, especially when the demands of the task get more complex.
Fear conditioning occurs in the basolateral amygdala, which receives glutaminergic input directly from thalamic afferents, as well as indirectly from prefrontal projections. The direct projections are sufficient for delay conditioning, but in the case of trace conditioning, where the CS needs to be internally represented despite a lack of external stimulus, indirect pathways are necessary.
The anterior cingulate is one candidate for intermediate trace conditioning, but the hippocampus may also play a major role. Presynaptic activation of protein kinase A and postsynaptic activation of NMDA receptors and its signal transduction pathway are necessary for conditioning related plasticity. CREB is also necessary for conditioning related plasticity, and it may induce downstream synthesis of proteins necessary for this to occur. Aversion therapy is a type of behavior therapy designed to make patients cease an undesirable habit by associating the habit with a strong unpleasant unconditioned stimulus.
Systematic desensitization is a treatment for phobias in which the patient is trained to relax while being exposed to progressively more anxiety-provoking stimuli e. This is an example of counterconditioning , intended to associate the feared stimuli with a response relaxation that is incompatible with anxiety  Flooding is a form of desensitization that attempts to eliminate phobias and anxieties by repeated exposure to highly distressing stimuli until the lack of reinforcement of the anxiety response causes its extinction.
Conditioning therapies usually take less time than humanistic therapies. This is sometimes the case with caffeine; habitual coffee drinkers may find that the smell of coffee gives them a feeling of alertness. In other cases, the conditioned response is a compensatory reaction that tends to offset the effects of the drug.
For example, if a drug causes the body to become less sensitive to pain, the compensatory conditioned reaction may be one that makes the user more sensitive to pain. This compensatory reaction may contribute to drug tolerance. If so, a drug user may increase the amount of drug consumed in order to feel its effects, and end up taking very large amounts of the drug.
In this case a dangerous overdose reaction may occur if the CS happens to be absent, so that the conditioned compensatory effect fails to occur. For example, if the drug has always been administered in the same room, the stimuli provided by that room may produce a conditioned compensatory effect; then an overdose reaction may happen if the drug is administered in a different location where the conditioned stimuli are absent.
These reflexive responses include the secretion of digestive juices into the stomach and the secretion of certain hormones into the blood stream, and they induce a state of hunger. An example of conditioned hunger is the "appetizer effect. The lateral hypothalamus LH is involved in the initiation of eating. The nigrostriatal pathway, which includes the substantia nigra, the lateral hypothalamus, and the basal ganglia have been shown to be involved in hunger motivation.
Conditioned emotional response[ edit ] Further information: Conditioned emotional response and Fear conditioning The influence of classical conditioning can be seen in emotional responses such as phobia , disgust, nausea, anger, and sexual arousal. A familiar example is conditioned nausea, in which the CS is the sight or smell of a particular food that in the past has resulted in an unconditioned stomach upset. Similarly, when the CS is the sight of a dog and the US is the pain of being bitten, the result may be a conditioned fear of dogs.
An example of conditioned emotional response is conditioned suppression. As an adaptive mechanism, emotional conditioning helps shield an individual from harm or prepare it for important biological events such as sexual activity. Thus, a stimulus that has occurred before sexual interaction comes to cause sexual arousal, which prepares the individual for sexual contact.
For example, sexual arousal has been conditioned in human subjects by pairing a stimulus like a picture of a jar of pennies with views of an erotic film clip. Similar experiments involving blue gourami fish and domesticated quail have shown that such conditioning can increase the number of offspring. These results suggest that conditioning techniques might help to increase fertility rates in infertile individuals and endangered species.
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