 Classical conditioning is a way of learning by identifying predictive relationship between two different stimuli. What does that mean? Let us see. For understanding classical conditioning, first we should know the meaning of certain terms. What is Unconditioned Stimulus, Unconditioned Response, then Conditioned Stimulus and Conditioned Response. So Unconditioned Stimulus is a stimulus which already produces a strong, consistent and automatic response. For example, giving food to an animal always produces salivation. So as soon as the animal keeps food into his mouth, there is consistent response of salivation and is automatic. And the response which is produced, which in this case is obviously salivation, it is an Unconditioned Response. So basically food is Unconditioned Stimulus and salivation is Unconditioned Response. With this example you might have understood that this response to Unconditioned Stimulus is innate to us and is produced without learning. Now this Unconditioned Response can be conditioned. That is, we learn to occur with any other stimulus as well, which originally did not produce this response. So when that learning will occur, we will call this new stimulus which is also producing that response as Conditioned Stimulus and the response will be Conditioned Response. So that Unconditioned Response has been conditioned to occur to a new stimulus which is known as Conditioned Stimulus. So what are the requirements for this learning to occur? Well we have to pair the new stimulus with original Unconditioned Stimulus like in classical experiment which was done by Pavlov. Ringing of bell was paired with giving of food for some time. So initially the animal was salivating in response to food but after some time salivation occurs with only ringing of bell as well. But for this remember that he rang the bell first and then in a short while gave the food that is the Unconditioned Stimulus which produced the salivation and when this process was repeated again and again over some time then only it was possible that ringing of the bell became a conditioned stimulus. So basically the dog associated the ringing of the bell with coming of food and that's why this salivation was occurring. So this association between two stimuli the new stimulus and the Unconditioned Stimulus is responsible for learning and that is why this form of learning is known as associative learning. Now there are few requirements for this type of conditioning to occur. First is while training or learning the new stimulus which needs to be conditioned should proceed the Unconditioned Stimulus and this should happen most of the times it should not be that randomly sometimes food is given and sometimes it is being paired with the new stimulus. The pairing should be done almost all of the times when food is given and also there should be a critical time gap between the two it should not be that you do ringing of the bell and then after half an hour you give the food. So critical time gap should be there and there should be consistent association between the two stimulus. So this consistency is very important if logically if you see suppose the stimulus is paired with the Unconditioned Stimulus only 50% of the times then the animal will not learn the association because such kind of association may occur by chance as well in the environment and the whole point of learning that association between different stimuli will be a waste. So basically by learning the association between two different stimuli the animal or for that matter any species actually learns to predict events in the environment. Also if repeatedly conditioned stimulus is not followed by Unconditioned Stimulus it can undergo extinction even after learning. Again if you see survival wise it is important because the animal has to forget about the stimuli which was previously important but now has become irrelevant as far as survival is concerned. Plus one thing more you remember here that conditioning can occur for both rewarding stimulus as we have seen in this example of food and also for noxious stimulus. For example suppose in dark in outside garden animal is attacked by a prey. So the animal will associate darkness with prey and hence with danger. So that is the learning for noxious stimuli. By the way the conditioning for rewarding stimulus is known as epititive conditioning and that for noxious stimulus is known as defensive conditioning. Fine so we saw what are the requirements of classical conditioning that there should be a critical time gap there should be pairing between those stimulus. Then we saw a concept about extinction of the learning if the pairing is totally abolished even after learning. Now there is another concept known as generalization. Now in the example of the dark and prey which we saw suppose even when the dog is at home and you switch off the light then also the dog may respond with the danger because he has associated darkness in the garden with prey but here the concept of darkness is being generalized as being the darkness anywhere is causing the danger so there is generalization of the learning which has occurred where a stimulus similar to condition stimulus elicits similar response. This actually happens when phobias develop that is a stimulus which is not actually important starts eliciting response of danger. But you might be amused to know that phobias are also treated with the concept of conditioning that is extinction which we saw before. So generalization is causing the phobias but the concept of extinction is used for treatment. In this the patients are presented with the stimulus slowly slowly and this is not followed by actual unconditioned stimulus which is eliciting a response and when it is repeated over a time this leads to extinction of the learned response. So suppose if anybody has a fear of darkness because some unfortunate event has occurred in the dark then the physician will slowly slowly expose the patient to little little darkness for a small small time and when over a period of time the person sees that there is no unfortunate incident occurring with darkness then over a period of time they may become comfortable with the dark stimuli. So in summary we dealt about what is classical conditioning what are its requirements what do you understand by certain terms like conditioned stimulus conditioned response unconditioned stimulus unconditioned response. Then we also saw the mechanism of extinction and generalization and how they are important for the development of phobias and their treatment. 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