" PAVLOV'S EXPERIMENT " 1976 IVAN PAVLOV, STIMULUS AND RESPONSE TESTS WITH DOGS PH10305

[00:00:00][Music] The first bite of a piece of food and saliva starts to flow in the mouth.

[00:00:38]That's something that's born with us.

[00:00:41]One example of an automatic reaction called a reflex. We're born with several reflexes. That's something we have in common with many animals. And so we can learn about our own reflexes by studying animals. For example, the saliva reflex in dogs was the basis for a famous series of experiments performed by the Russian scientist Ivon Pavlov. To see what he learned, we can reproduce some of his experiments. A model of a dog's head can demonstrate how saliva is secreted into the mouth.

[00:01:20]There are three pairs of salivary glands. This tube represents a narrow duct that carries saliva from a gland near the dog's right ear. In our experiment, we'll want to measure the amount of saliva being produced. And we can arrange that by a simple and painless operation. To explain the operation, we'll use our model.

[00:01:48]First part of the duct is loosened. Then a small hole is made in the cheek. This will allow the saliva to flow outside the mouth where we can see it.

[00:02:18]Five of the six glands will still be secretting saliva inside the mouth to start the process of digestion.

[00:02:43]The dog can eat normally and we can see saliva flowing, but it's difficult to measure the amount. We can correct that by attaching this simple device. Saliva will drip slowly down the slide and we can count the drops. An adhesive will hold it in place.

[00:03:10]Now we can start the experiment. We're using basically the same elements that Pavlo used. We know that the dog responds normally to food and we can count the drops of saliva being produced.

[00:03:40]Now, a metronome normally has nothing to do with food. But can the sound of a metronome have an effect on the reflex that produces saliva? The metronome can be started and stopped by remote control.

[00:04:04]A few seconds before serving the food, we'll start the metronome. In this first trial, there seems to be no change in the reflex. Saliva is secreted when the dog starts to eat.

[00:04:34]We'll repeat the same procedure several times. After a few trials, saliva is being produced before the food is served. Still later, after more repetitions, we can draw some definite conclusions.

[00:04:53]The sound of the metronome has become a stimulus that causes saliva to flow even before any food is provided. We've produced what Pavlov called a conditioned reflex. Suppose we change the tempo of the metronome. Will the dog respond to the altered stimulus? This time no food will be given.

[00:05:26]On the first trial, there is a response. Saliva is being produced, but in a smaller quantity. We'll run several trials at various tempos, including the original one. At this tempo, and only at this one, we'll reinforce the conditioning by giving food.

[00:05:51]This chart shows the amount of saliva produced during several trials at varying tempos of the metronome. The greatest amount was produced at the original tempo, the one used during the conditioning process.

[00:06:05]The more the tempo varied from the original, the smaller the amount of saliva. After several trials, we can notice a further change. At this tempo, there's no longer any saliva being produced. Eventually, the conditioned response becomes limited to a very narrow range within five or six beats per minute of the original tempo. Now, is it possible to remove the conditioning entirely?

[00:06:41]We're using the original temple, but for the first time, we're not giving food We'll run several trials in a period of a few hours, all without food. Here are the results. The conditioned response falls off. And on the eighth trial, no saliva is produced at all. But actually, the conditioning hasn't been removed as yet.

[00:07:33]On the following day, some saliva is produced on the first few trials. Finally, after several days of repeated trials without food, the conditioned response has disappeared entirely. By means of experiments like these under controlled conditions in a laboratory, we've learned a great deal about why animals behave as they do in everyday life.

[00:08:03][Music] And since human beings also have reflexes, the study of conditioning can help us understand our own patterns of behavior. Does conditioning play a part in the learning of new skills? Does it affect our ability to cope with the world around us?

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