Classical Conditioning

Classical Conditioning

Classical conditioning is also referred to as associative learning or Pavlovian
conditioning, after its primary founder, the Russian physiologist Ivan Petrovich
Pavlov (1849-1936). Pavlov’s original studies involved examining digestion
in dogs. The first step in digestion is salivation. Pavlov developed an apparatus
that allowed him to measure the amount of saliva a dog produced
when presented with food. Dogs do not need to learn to salivate when food
is given to them—that is an automatic, reflexive response. However, Pavlov noticed that, with experience, the dogs began to salivate before the food was
presented, suggesting that new stimuli had acquired the ability to elicit the
response. In order to examine this unexpected finding, Pavlov selected specific
stimuli, which he systematically presented to the dog just before food
was presented. The classic example is the ringing of a bell, but there was
nothing special about the bell per se. Dogs do not salivate in response to a
bell ringing under normal circumstances. What made the bell special was its
systematic relationship to the delivery of food. Over time, the dogs began to
salivate in response to the ringing of the bell even when the food was not
presented. In other words, the dogs learned to associate the bell with food
so that the response (salivation) could be elicited by either stimulus.

In classical conditioning terminology, the food is the unconditioned
stimulus (US). It is unconditioned (or unlearned) because the animal naturally
responds to it before the experiment has begun. The sound of the bell
ringing is referred to as the conditioned stimulus (CS). It is not naturally effective
in eliciting salivation—for it to be so, learning on the part of the subject
is required. Salivating in response to food presentation is referred to as the unconditioned response (UR), and salivating when the bell is rung is referred
to as the conditioned response (CR). Though it would seem that saliva
is saliva, it is important to differentiate the conditioned from the unconditioned
response, because these responses are not always identical. More
important, one is a natural, unlearned response (the UR), while the other
requires specific learning experiences in order to occur (the CR).

Classical conditioning is not limited to dogs and salivation. Modern researchers
examine classical conditioning in a variety of ways. What is important
is the specific pairing of some novel stimulus (the CS) with a stimulus
that already elicits the response (the US). One common experimental procedure
examines eye blink conditioning in rabbits, where a brief puff of air
to the eye serves as the US, and the measured response (UR) is blinking. A
tone, a light, or some other initially ineffective stimulus serves as the CS. After
many pairings in which the CS precedes the air puff, the rabbit will begin
to blink in response to the CS in the absence of the air puff. Another common
behavior that is studied in classical conditioning research is conditioned
suppression. Here a CS is paired with an aversive US, such as a mild
electric shock. Presentation of the shock disrupts whatever behavior the animal
is engaged in at the time, and with appropriate pairing over time, the CS
comes to do so as well. A final example that many humans can relate to is
taste aversion learning. Here a specific taste (CS) is paired with a drug or
procedure that causes the animal to feel ill (US). In the future, the animal
will avoid consuming (CR) the taste (CS) associated with illness (US). Taste
aversions illustrate the fact that all forms of conditioning are not created
equal. To learn a conditioned eye blink or salivation response requires many
CS-US pairings, while taste aversions are often learned with only one pairing
of the taste and illness.