More Drool, Please

At the Institute of Experimental Medicine in St. Petersburg, Russia, physiologist Ivan Pavlov was studying the digestive systems of dogs. In a series of carefully controlled experiments, he hoped to answer several questions. How did the amount of food eaten affect the quantity of saliva a dog produced? Did the type of food or the time it was served make a difference?

Normally, the sight or smell of food caused the dogs’ salivary glands to swing into action, producing drool and beginning the digestive process. But one day Pavlov noticed something odd when an assistant entered the research area wearing a white lab coat. One of the dogs began to salivate even though the assistant wasn’t carrying food. The same thing happened when an empty metal food cart was wheeled into the room – slobber, even when there was no food around.

Pavlov believed that the dog had been conditioned to salivate. Because assistants normally wore white coats during feedings and wheeled carts into the room, the dog had unconsciously learned to connect the sight of the coat and the clang of the cart to food. In time, just the white coat or the cart alone was enough to jumpstart the drooling process.

Pavlov set up a series of experiments where he paired food with various sights or sounds. In one, he rang a bell just before food was delivered. After a few tries, the sound of the bell itself was enough to cause the dog to drool.

Intrigued by the response, Pavlov devoted the rest of his life to studying conditioned learning. In 1904, the Noble Prize for Medicine or Physiology was awarded to Ivan Pavlov for his work on classical conditioning. His discovery laid the groundwork for a whole new branch of science – psychology, the study of human behavior.

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