Classical Conditioning

Classical conditioning was first systematically investigated by Ivan Pavlov in
the late 1800’s and early 1900’s. Classical conditioning involves the transfer
of control of an elicited response from one stimulus to another, previously
neutral, stimulus. Pavlov discovered classical conditioning accidentally while
investigating digestion in dogs. A dog was given meat powder in its mouth to
elicit salivation. After this process had been repeated a number of times, the dog would start salivating before the meat powder was put in its mouth.
When it saw the laboratory assistant, it would start to salivate, although it
had not initially salivated at the sight. Pavlov devoted the rest of his long career
to the phenomenon of classical conditioning.
In classical conditioning, a response is initially elicited by an unconditioned
stimulus (US). The US is a stimulus that elicits a response without any
prior experience. For example, the loud sound of a balloon bursting naturally
causes people to blink their eyes and withdraw from the noise. The response
that is naturally elicited is called the unconditioned response (UR).
If some stimulus reliably precedes the US, then over time it, too, will come to
elicit a response. For example, the sight of an overfull balloon initially does
not elicit blinking of the eyes, but if the sight of the balloon reliably precedes
the loud noise that comes when it bursts, people eventually come to blink
and recoil at the sight of an overfull balloon. The stimulus with the new
power to elicit the response is called the conditioned stimulus (CS), and the
response elicited by the CS is called the conditioned response (CR).
Classical conditioning occurs with a variety of behaviors and situations.
For example, a person who was stung by a wasp in a woodshed may now experience
fear on approaching the woodshed. In this case, the building becomes
a CS eliciting the CR of fear because the wasp’s sting (the US) elicited
pain and fear (the UR) in that place. To overcome the classical conditioning,
the person would need to enter the woodshed repeatedly without incident.
If the woodshed was no longer paired with the painful sting of the
wasp, over time the CR would extinguish.
Many phobias are thought to arise through classical conditioning. One
common successful treatment is systematic desensitization, in which the person,
through progressive steps, gradually faces the feared object or situation
until the fear CR extinguishes. Classical conditioning has been recognized
as the culprit in food aversions developed by people receiving chemotherapy
treatments for cancer. In this case, the food becomes a CS for illness (the
CR) by being paired with the chemotherapy treatment (the US) that later
elicits illness (the UR). Using more advanced principles of classical conditioning
learned through research with nonhumans, people are now able to
reduce the degree of aversion that occurs to regular meals, thus preventing
the person from developing revulsions to food, which would further complicate
the treatment of the cancer by introducing potential nutritional problems. 485