Chapter 3 - Classical Conditioning: Foundations
The Early Years of Classical Conditioning
Summited work on classical conditioning in his PhD dissertation at the University of Pennsylvania. He repeatedly tested the
knee-jerk reflex of college students by sounding a bell 0.5 second before hitting the patellar tendon just below the kneecap. Soon
enough the sounding of the bell set off the knee-jerk reflex. He did not explore deeper into his findings and did not receive much
Ian P. Pavlov
A Russian Psychologist, studies on classical conditioning were an extension of digestion by developing surgical techniques that
enabled dogs to survive for many years with artificial fistulae that permitted the collection of various digestive juices.
He found that the dogs secreted stomach fluids in response to the sight of food or seeing the person that normally feeds them
They referred to this as psychic secretions because they seemed to be a response to the expectation or thought of food.
The Discoveries of Vul’fson and Snarskii
They preformed the first systematic studies of classical conditioning in Pavlov’s laboratory.
They focused on Salivary Glands since they are the first glands to be involved in the digestion/ breakdown of food.
Vul’fson studied salivary responses of the dogs by giving them various substances, which after awhile they began to salivate just
by the sight of these substances.
Snarskii took this a step further by giving them artificial substances. For example: artificially coloured black water that was sour
(lemon water). After a few times of having this black sour water, the dog began to salivate with just the sight of black water.
They found that these substances created distinctive texture and taste sensations in the mouth. This sensation is called
The dogs learned to associate the sight of these foods with salivation. This is called object learning, which is the association of
one feature of an object with another.
The Classical Conditioning Paradigm
Pavlov’s procedure for the study of conditioned salivation involved two stimuli: the tone or light that does not elicit salivation
and the second stimulus is the food or taste of a sour substance.
Conditioned Stimulus (CS): the light or tone, because its effectiveness of this stimuli on eliciting salivation depended on pairing
it with the presentation of food.
Unconditioned Stimulus (US): the food or sour substances, because its effectiveness on eliciting salivation did not depend on
any prior training
Conditional Response (CR): the salivation that eventually came to be elicited by the tone or light
Unconditional Response (UR): the salivation that was always elicited by the food our sour substance
Most contemporary experiments on Pavlovian conditioning are done on domesticated rats, rabbit’s ad pigeons using procedure
developed by North American scientists during the second half of the twentieth century.
Watson and Rayner believed that infants, at first, were limited in their emotional responses.
They assumed that “there must be some simple method by means f which the range of stimuli which can call out all these
emotions and their compounds is greatly increased”. This simple method was Pavlovian conditioning.
In a famous experiment, Rayner and Watson conditioned a fear response to a white rat in nine-month old Albert.
Albert was fine with the rat until they began to make a loud noise (hammer hitting a steel bar) behind him while they put the rat
After the first two times, Albert was reluctant to touch the rat
After the first five times, Albert showed strong fear responses to the rat such as whimpering, crying, leaning away from the rat as
much as he could and sometimes he would crawl on all fours away from the rat.
These fear responses were not evident when he was presented with his toy blocks, but the conditioned fear did generalize to other
furry things such as a rabbit, fur coat, cotton wool, a dog and a Santa Claus mask.
Fear and anxiety are the sources of considerable human discomfort and if sufficiently severe, they can lead to serious
psychological and behavioural problems.
Since it is hard to experiment on human subjects, most of the research on fear conditioning has been conducted with laboratory
mice and rats.
Unlike Albert who showed signs of fear by whimpering and crying, rats show their fear by freezing. Freezing is defined as
immobility of the body (except for breathing) and the absence of movement of the whiskers associated with sniffling.
Freezing has probably evolved because animals that are motionless are less likely to be seen by their predator.
Direct measurement of freezing as an index of conditioned fear has become popular, especially in neurobiological studies of fear. There are two other direct measures of immobility, both involving the suppression of ongoing behaviour that is referred to as
In one case the ongoing behaviour that is measured is licking a drinking spout that contains water. The animals are slightly water
deprived and therefore lick readily when placed in the experimental chamber. If a fear conditioned stimulus (ex// tone.) is
presented then it takes longer for them to do a certain amount of licks and their behaviour is suppressed. This is called the lick-
Another technique for indirect measurement of conditioned fear is the conditioned emotional response (CER). In this
procedure, rats are trained to press a response lever for a food reward in a small experimental chamber. Once the rats are pressing
the lever at a steady rate, a fear conditioned is introduced, consisting of a tone or light paired with a brief shock. They begin to
suppress their lever pressing during the CS due to fear.
In order to measure the suppression of the lever presses, the following formula is used:
*See text page 73 for example.
Suppression Ratio= CS Responding ÷(CS Responding + pre-CS Responding)
the eye blink reflex is an early component of the startle response and occurs in a variety of species.
Eyeblink conditioning continues to be a very active area of research because it provides a powerful tool for the study of problems
in development, age and Alzheimer’s disease.
It is also used in studies of the neurobiology of learning. This knowledge has in turn made eyeblink conditioning useful in studies
of autism, fetal alcohol syndrome and obsessive compulsive obsessive disorder.
It is easy to get someone to blink, all you have to do is clap your hands or blow a puff of air toward the person’s eye. If the air
puff is preceded by a brief tone, the person will learn to blink when the tone comes on, in anticipation of the air puff.
A study of eyeblink conditioning in 5-month-old infants illustrates this technique. For two sessions, the CS was a tone presented
for 750 milliseconds, and the US was a gentle puff of air delivered to the right eye through a plastic tube. The results of the
experiments showed that classical conditioning required the pairing of a CS and US. It also showed that learning was not
observable at the first session but at the second session they began to learn that the CS was related to the US.
Recent interest in eyeblink conditioning in humans stems from the fact that substantial progress has been made in understanding
the neurobiological substrates of this type of learning neurobiological investigations of eyeblink conditioning have been
conducted primarily with domesticated rabbits which was developed by Gormezano.
Rabbits are ideal for this type of research because they are sedentary and rarely blink in the absence of an air puff or irritation of
the eye. In this experiment they are placed in an enclosure and attached to equipment that enables measurements of the blink
response. The US to elicit blinking is provided by a mild irritation of the skin below the eye with a brief 0.1-second electrical
current. The Cs may be a light, a tone or a mild vibration in the rabbit’s abdomen. The CS is presented for half a second and is
followed immediately by the delivery of the US. The US elicits a rapid and vigorous eye closure. As the CS is repeatedly paired
with the US, the eyeblink is also made with the CS. Rabbit eyeblink conditioning is relatively slow, requiring several hundred
trials for substantial levels of conditioned responding.
Sign Tracking/ Autoshaping Paradigm
Sign tracking is investigated in the laboratory by presenting a discrete localized visual stimulus just before each delivery of a
small amount of food.
Brown and Jenkins preformed the first experiment of this sort in 1968 with pigeons. They were placed in an experimental
chamber and had a small circular key that could be illuminated and that the pigeons could peck on. Periodically the birds
were given access to food and the key was lit for 8 seconds immediately before each food delivery. You would assume that
when they pigeons saw the key light they would go over to the food dish and wait for food but instead they started pecking at
the key light even though it was not necessary to gain access to food. Presenting the key light at random times or unpaired
with food does not lead to pecking.
Since its discovery, many experiments have been done on sign tracking in a variety of species, including chicks, quail,
goldfish, rats, rhesus monkeys, squirrel monkeys, and human adults and children.
Sign tracking occurs only in situations where the CS is localized and therefore can be approached and tracked.
In one study conducted with laboratory rats, a localized sound and light were compared as conditioned stimuli for food. Only
the light CS generated sign tracking behaviour. The auditory CS elicited approach to the food cup rather than approach to the
sound source. These type of experiments illustrate that for sign tracking to occur, the CS has to be of the proper modality and
Research is also underway to develop sign tracking as a model system for studying the role of incentive motivation in drug
Learning What Tastes Good or Bad
A taste preference may be learned if a flavor is paired with nutritional repletion or other positive consequences. In contrast, a conditioned taste aversion is learned if ingestion of a novel flavor is followed by an aversive consequence such as
indigestion or food poisoning.
The typical learning aversion experience involves eating a distinctively flavoured food and then getting sick. Such a flavor-illness
experience can produce a conditioned food aversion in just once trial, and the learning can occur even if the illness is delayed a
few hours after the ingestion of the food.
In 20% of the cases, the individuals were certain that their illness was not caused by the food they at. They learned an aversion to
the food. This indicates that food aversion can be independent of rational thought process and can go against a person’s
conclusions about the cause of their illness.
Experimental studies of taste-aversion have been conducted with people in situations where they encounter illness during the
course of medical treatment such as chemotherapy. Chemotherapy often causes nausea as aside effect. Both children and adult
cancer patients have been shown to acquire aversions of foods eaten before a chemotherapy session. Such conditioned aversions
may contribute to the lack of appetite that is a common side effect of chemotherapy.
Conditioned food aversions also may contribute to the suppression of food intake or anorexia observed in other clinical
situations. The anorexia that accompanies growth of some tumors may result from food-aversion learning. Animal research
indicates that the growth of tumors can result in the conditioning of aversions to food ingested during the disease.
People suffering from anorexia nervosa experience digestive disorders that may increase their likelihood of learning food
Food aversion learning may also contribute to loss of appetite seen in people suffering from severe depression.
Taste-aversion learning in tested on animals and is a result of the pairing of a CS (a taste) and a US (drug injection or radiation
Two unique features of taste aversions is that it can be learnt in just one trial and that it occurs even if the illness is not
experiences till several hours after.
A flavour can also be made not pleasant and hard to tolerate by pairing it with another taste that is already disliked.
How people learn to like or dislike an initially neutral flavour is part of the general phenomenon of evaluative conditioning. In
evaluative conditioning, our evaluation or liking of a stimulus changes by virtue of having that stimulus associated with
something we already like or dislike. Excitatory Pavlovian Conditioning procedures
o Organisms learn an association between the conditioned and unconditioned stimuli.
o As a result of this association the CS activates behavioral and neural activity related to the US in the absence of the
actual presentation of the US
Common Pavlovian Conditioning procedures
o One of the major factors that determines the course of classical conditioning is the relative timing of the CS and the US.
o Seemingly small and trivial variations in how a CS is paired with a US can have profound effects on how vigorously
and when the CR occurs
Five Classical conditioning Procedures
1: short delayed conditioning
o most frequently used