Ivan Pavlov was a Russian physiologist whose research on the physiology of digestion led to the development of the first experimental model of learning, Classical Conditioning. Most of his research was gathered studying salivating dogs. An illustrated review of Pavlov's experiments is available on the [Discovery Web Site].

Pavlov was born on September 14, 1849, at Ryazan, Russia. Because he was born into a large family, poverty was always an issue. His father, Peter Dmitrievich Pavlov, was the village priest and young Ivan tended to the church property. Pavlov inherited many of his father's characteristics including a strong will to succeed.

The oldest sibbling, Ivan Pavlov was also among the healthiest. He began school at the Ryazan Ecclesiastical High School. Pavlov and his brothers eventually entered the Ryazan Ecclesiastical Seminary. At the Seminary, he planned to pursue a career in theology. However, after being introduced to the works of Charles Darwin and Ivan Sechenov, Pavlov decided to transfer to the University of St. Petersburg to gain knowledge about natural science. There, Pavlov gained great respect for a professor of physiology, Cyon. Due to Cyon's enthusiasm for physiology, he decided to become a physiologist during his third year. At that point, Pavlov started work as an assistant in a laboratory in which he earned 50 rubles a month.

Eventually, Pavlov's research on the physiology of digestion would earn him the Nobel Prize. As a skilled surgeon, he was able to implant small stomach pouches in dogs to measure the secretion of gastric juices produced when the dogs began to eat. With the help of his assistants, he was able to condition the dogs to salivate at the click of a metronome. As his work progressed, Pavlov established the basis for conditioned reflexes and the field of classical conditioning.

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Theory Pavlov concluded that he was able to pair a neutral stimulus with an excitatory one and have the neutral stimulus eventually elicit the response the was associated with the original, unlearned reflex. In Classical Conditioning terminology, an unconditioned stimulus (US) is an event that causes a response to occur, which is referred to as the unconditioned response (UR). And, in Pavlov's study with dogs, the food within the dog's mouth is the US, and the salivation that results is the UR. Pavlov took a step further and added an element known as the nonexcitatory, conditioned stimulus (CS), which is paired with the US.
Pavlov used a metronome as the CS which he rang first, then fed the dogs. This pairing would eventually establish the dog's conditioned response of salivating to the sound of the metronome. After repeating this procedure several times, Pavlov was able to remove the US (food) and by only ringing the bell the dogs would salivate (CR). Since the bell alone now produced the unconditioned response (salivation), the association had been established (Conditioned). Pavlov continued to present the CS with any pairing with the US until the CR no longer occurred. This elimination of the CR is known as extinction. However, waiting a few days and then reintroducing ticking metronome resulted in the dogs once again salivating to the CS. Pavlov termed this, spontaneous recovery.
Pavlov continued of the conditioned response. He replaced the metronome with other stimuli for use as the CS. He conditioned the dogs using a buzzer, the flash of a light, a touch on the dog's harness, and the use of different pitches of a whistle in which the dogs had to differentiate between to determine which pitch resulted in access to food.

Pavlov's experimental research gained much respect throughout Russia as well as America and the rest of the nations. Although he began his investigations late in life he managed to develop the major constructs of a fully realized field of learning. He summarized his discoveries in his remarkable book, Conditioned Reflexes.