A note on Pavlovian (classical) conditioning, a form of artificial animal behavior modification.

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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Pavlovian (Classical) Conditioning
Classical conditioning is a learning process that occurs through associations between an
artificial stimulus (conditioned) and a naturally occurring stimulus (unconditioned). It was
discovered by Russian physiologist Ivan Pavlov. It is a type of associative learning.
Classical conditioning occurs when a conditioned stimulus is paired with an unconditioned
stimulus. Usually, the conditioned stimulus is neutral (e.g., the sound of a bell), the
unconditioned stimulus is natural (e.g., the taste of food). The unconditioned (natural)
response to the unconditioned stimulus is a reflex / unlearned response (e.g., salivation).
After pairing between the two stimuli is repeated, the organism exhibits a response to the
conditioned stimulus when the conditioned stimulus is presented alone.
Components of Classical Conditioning:
 Unconditioned stimulus: it is a natural stimulus that causes a natural/unconditioned
response, i.e. smell of food.
 Unconditioned response: it is the natural response to unconditioned stimulus, i.e. dogs
salivate when they smell food.
 Neutral stimulus: it is a stimulus that naturally does not affect an animal, i.e. sound of
a bell.
 Conditioned stimulus: when the neutral stimulus is associated with an unconditioned
stimulus, it becomes a conditioned stimulus.
 Conditioned response: the response to the conditioned stimulus is called a
conditioned response.
Pavlov's Research:

2. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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During his research on the physiology of digestion in dogs, Pavlov noticed that his dogs
began to salivate in the presence of the technician who normally fed them, rather than
simply salivating in the presence of food. Putting these observations to an experimental
test, Pavlov presented a stimulus (e.g. the sound of a bell) and then gave the dog food;
after a few repetitions, the dogs started to salivate in response to the stimulus. Pavlov
concluded that if a particular stimulus in the dog's surroundings was present when the
dog was given food then that stimulus could become associated with food and cause
salivation on its own.
 The unconditioned stimulus (US) was the dog food.
 The unconditioned response (UR) was salivating upon seeing dog food.
 The bell's sound is originally a neutral stimulus.
 After conditioning, the bell's sound became the conditioned stimulus (CS).
 The conditioned response (CR) was salivating upon the sound of the bell.
Pavlov found out that learning occurred most rapidly when the interval between the
conditioned stimulus and the unconditioned stimulus was short.
MECHANISM OF CLASSICAL CONDITIONING:
Classical conditioning involves forming an association between two stimuli resulting in a
learned response. There are three phases of this process:
Phase 1 - Before Conditioning: The first part of the classical conditioning process requires
a naturally occurring stimulus that will automatically cause a response. Salivating in
response to the smell of food is a good example of a naturally occurring stimulus. During
this phase of the processes, the unconditioned stimulus results in an unconditioned
response, i.e. presenting food naturally and automatically triggers a salivation response.
At this point, there is also a neutral stimulus that produces no effect - yet. It isn't until this

3. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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neutral stimulus is paired with the unconditioned stimulus that it will come to evoke a
response.
Phase 2 - During Conditioning: During the second phase of the classical conditioning
process, the previously neutral stimulus is repeatedly paired with the unconditioned
stimulus. As a result of this pairing, an association between the previously neutral
stimulus and the unconditioned stimulus is formed. At this point, the once neutral stimulus
becomes known as the conditioned stimulus. The subject has now been conditioned to
respond to this stimulus.
Phase 3 - After Conditioning: Once the association has been made between the
unconditioned stimulus and the conditioned stimulus, presenting the conditioned stimulus
alone will come to cause a response even without the unconditioned stimulus. The
resulting response is known as the conditioned response.
PRINCIPLES OF CLASSICAL CONDITIONING:
Five key principles of classical conditioning are as follows:
Acquisition: Acquisition is the initial stage of learning when a response is first established
and gradually strengthened. During the acquisition phase of classical conditioning, a
neutral stimulus is repeatedly paired with an unconditioned stimulus. After an association
is made, the subject will begin to emit a behavior in response to the previously neutral
stimulus, which is now known as a conditioned stimulus. It is at this point that we can say
that the response has been acquired.
Extinction: Extinction is when the occurrences of a conditioned response decreases or
disappears. In classical conditioning, this happens when a conditioned stimulus is no
longer paired with an unconditioned stimulus. For example, if the smell of food (the

4. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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unconditioned stimulus) had been paired with the sound of a bell (the conditioned
stimulus), it would eventually come to evoke the conditioned response of hunger.
However, if the unconditioned stimulus (the smell of food) were no longer paired with the
conditioned stimulus (the bell), eventually the conditioned response (hunger) would
disappear.
Spontaneous Recovery: Sometimes a learned response can suddenly re-emerge even
after a period of extinction. Spontaneous recovery is the reappearance of the conditioned
response after a rest period or period of lessened response. For example, after training
a dog to salivate to the sound of a bell, we stop reinforcing the behavior and the response
eventually becomes extinct. After a rest period during which the conditioned stimulus is
not presented, we suddenly ring the bell and the animal spontaneously recovers the
previously learned response.
Stimulus Generalization: Stimulus generalization is the tendency for the conditioned
stimulus to cause similar responses after the response has been conditioned. For
example, if a dog has been conditioned to salivate at the sound of a bell, the animal may
also exhibit the same response to stimuli that are similar to the conditioned stimulus, i.e.
whistle, etc.
Stimulus Discrimination: Discrimination is the ability to differentiate between a conditioned
stimulus and other stimuli that have not been paired with an unconditioned stimulus. For
example, if a bell tone were the conditioned stimulus, discrimination would involve being
able to tell the difference between the bell tone and other similar sounds. Because the
subject can distinguish between these stimuli, he or she will only respond when the
conditioned stimulus is presented.