Which brings us to the most famous of the Russian researchers, Ivan Petrovich Pavlov (1849-1936). After studying for the priesthood, as had his father, he switched to medicine in 1870 at the Military Medical Academy in St. Petersburg. It should be noted that he walked from his home in Ryazan near Moscow hundreds of miles to St. Petersburg!

In 1879, he received his degree in natural science, and in 1883, his MD. He then went to study at the university of Leipzig in Germany. In 1890, he was offered a position as professor of physiology at his alma mater, the Military Medical Academy, which is where he spent the rest of his life. It was in 1900 that he began studying reflexes, especially the salivary response.

In 1904, he was awarded the Nobel Prize in physiology for his work on digestion, and in 1921, he received the Hero of the Revolution Award from Lenin himself.

Pavlovian (or classical) conditioning builds on reflexes:  We begin with an unconditioned stimulus and an unconditioned response -- a reflex!  We then associate a neutral stimulus with the reflex by presenting it with the unconditioned stimulus.  Over a number of repetitions, the neutral stimulus by itself will elicit the response!  At this point, the neutral stimulus is renamed the conditioned stimulus, and the response is called the conditioned response.

Or, to put it in the form that Pavlov observed in his dogs, some meat powder on the tongue makes a dog salivate.  Ring a bell at the same time, and after a few repetitions, the dog will salivate upon hearing the bell alone -- without being given the meat powder!

Pavlov agreed with Sechenov that there was inhibition as well as excitation.  When the bell is rung many times with no meat forthcoming, the dog eventually stops salivating at the sound of the bell.  That’s extinction.  But, just give him a little meat powder once, and it is as if he had never had the behavior extinguished:  He is right back to salivating to the bell.  This spontaneous recovery strongly suggests that the habit has been there all alone.  The dog had simply learned to inhibit his response.

Pavlov, of course, could therefore condition not only excitation but inhibition.  You can teach a dog that he is NOT getting meat just as easily as you can teach him that he IS getting meat.  For example, one bell could mean dinner, and another could mean dinner is over.  If the bells, however, were too similar, or were rung simultaneously, many dogs would have something akin to a nervous breakdown, which Pavlov called an experimental neurosis.

In fact, Pavlov classified his dogs into four different personalities, à la the ancient Greeks:  Dogs that got angry were choleric, ones that fell asleep were phlegmatic, ones that whined were melancholy, and the few that kept their spirits up were sanguine!  The relative strengths of the dogs’ abilities to activate their nervous system and calm it back down (excitation and inhibition) were the explanations.  These explanations would be used later by Hans Eysenck to understand the differences between introverts and extraverts!

Another set of terms that comes from Pavlov are the first and second signal systems.  The first signal system is where the conditioned stimulus (a bell) acts as a “signal” that an important event is to occur -- i.e. the unconditioned stimulus (the meat).  The second signal system is when arbitrary symbols come to stand for stimuli, as they do in human language.