How it began
In 1890 Ivan Pavlov was asked to organize the Physiology Department of the Institute of Experimental Medicine in Saint Petersburg, where he studied the digestive glands of dogs. He noticed that the dogs began to salivate in the presence of the technician who normally fed them, not only in the presence of food. He developed the concept of the conditioned reflex, which he called the conditional reflex, jointly with his assistant Ivan Tolochinov in 1901. Tolochinov reported the results in Helsinki in 1903, and Pavlov explained them more fully that year at the International Medical Congress in Madrid.
Before it existed
Earlier experiments on digestion were acute, meaning that the animal underwent vivisection that ultimately killed it. Pavlov's laboratory instead kept a full-scale kennel and observed the dogs' normal physiological processes over long periods, using surgically implanted fistulas to collect secretions. His 1897 book The Work of the Digestive Glands summarized twelve years of this research, and it was within these long-running experiments that the learned salivation response was observed.
How it works
If a sound such as a buzzer or metronome was presented before food was given, the dog came to associate the sound with the food and would later salivate at the sound alone. Pavlov's writings record many different stimuli, including electric shocks, whistles, metronomes, tuning forks and visual signals as well as a bell. The salivation produced by the signal is the conditioned reflex, an automatic response acquired through experience.
Who pushed back
Priority was not entirely Pavlov's. Edwin B. Twitmyer at the University of Pennsylvania published similar research in 1902, a year before Pavlov published his. Later scholars have also questioned the popular image of the experiment: in 1994 A. Charles Catania cast doubt on whether Pavlov ever used a bell, and others replied with references suggesting that he did. Bertrand Russell wrote that it was open to question whether Pavlov's methods could cover the whole of human behavior.
What lasted
Pavlov received the 1904 Nobel Prize in Physiology or Medicine for his work on digestion, not for conditioning, but the Nobel organization notes that his research on behavior influenced fields beyond physiology and became the basis of behaviorism. His work became known in the West through John B. Watson and B. F. Skinner, and conditioning became a key concept in comparative psychology.
Where it stands today
Studies of classical conditioning continue to be central to modern behavior therapy. The Pavlov Institute of Physiology of the Russian Academy of Sciences, which Pavlov founded in 1925, carries his name, and the term Pavlov's dog is among several named in his honor.
