Classical Conditioning

Modified: 2020-03-27

Ivan Pavlov was a Russian physiologist. During the early 20th century he worked on describing the process of digestion. He developed techniques of collecting saliva from dogs. He did so because salivation is the first step in digestion. He presented meat powder to his dogs, and then collected the saliva. However, he soon noticed that as the dogs became familiar with the experimental routine they began to salivate before they received the meat powder.

That observation led Pavlov to investigate the process whereby dogs learned to associate the experimental routine with the meat powder. That decision marked the time that Pavlov's research became psychological instead of physiological. He systematically presented stimuli, e.g., metronomes, lights, buzzers, to his dogs and then followed those with meat powder. He soon found that the dogs easily learned to salivate to the presentation of any stimulus associated with the meat powder.

He called the meat powder the unconditioned stimulus or UCS, because dogs did not need to learn that association. It was already "built-in" to each dog. He called the stimulus he chose to present first the conditioned stimulus or CS. He called it the conditioned stimulus because the dogs would not salivate to it at first. They would only salivate to it after it had been associated with the UCS.

When the dog salivated to the meat powder, Pavlov called that response the unconditioned response or UCR. He called it that because it occurred to the UCS. When the dog salivated to the stimulus Pavlov chose and presented prior to the UCS, he called that the conditioned response or CR. Again, he called it that because it occurred to the CS. Although the UCR and CR are very similar, they are not identical.

So, Pavlov's discovery was that a new stimulus can lead to a new response similar to a naturally occurring stimulus and response. The keys to classical conditioning are the temporal (time) relationships of the CS and the UCS, and also, how well the CS predicts the likelihood of the UCS.

Let us review. Pavlov's discovery is now called classical or respondent conditioning. The UCS-->UCR relationship is naturally occurring; it is not learned. Salivation in dogs occurs to the presentation of meat powder because that is part of the biology of being a dog. A similar example in humans is an air puff to the eye and blinking. Humans will blink if air is blown gently into their eye. The CS at first leads to no observable behavior. But, as the CS is followed by the UCS over and over, dogs start to salivate when the CS is presented, and humans, also, start to blink to a light when that light (a CS) is presented prior to the puff of air.

So, one can think of classical conditioning as the pairing of a CS and a UCS in time, with the CS occurring first, or, CS-->UCS.

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