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Chapter 3
Two Early Connectionist
Theories
Presented By:
Shayna N. Lamkin
Chapter Highlights
* Introduction
* Pavlov’s Conditioning
* Basic Principles of Pavlovian Conditioning
* Excitation and Inhibition
* Applications and Implications
* Thorndike’s Early Connectionism
* Thorndike’s Basic Ideas
* Elaborations
* Comparison of Thorndike with Pavlov
* Thorndike’s Place in Psychology
Introduction
First Psychological laboratory was founded by Wilhelm
Wundt in Germany, 1897.
*A marking point at which modern scientific psychology was
placed on a definite institutional footing.
Wundt and his colleagues wanted to understand human
sensations and thoughts and feelings. They wanted to take the
continuous flux of conscious awareness and analyze it into its
basic components.
*Are memory images the same as sensations?
*Are feelings a special kind of sensation or are they
something really different?
*How is the intensity of a sensation related to the
intensity of the physical stimulus that produces it?
This kind of psychology, developed in Germany, became
to a great extent the standard for the rest of Europe and
for America.
Pavlov’s Conditioning
1904-Ivan P. Pavlov (1849-1936) won the Nobel Prize in
physiology and medicine for his work on digestion.
His research consisted of opening a fistula in the wall of a
dog’s stomach. He noticed that the stomach secretions he
was studying were first triggered not by food reaching the
stomach but by chewing or even just the sight of food, and
he began to find this anticipatory secretion the most
interesting aspect of the digestive process.
Through this new line of research (Pavlov 1960, original
date 1927), he became even more famous as the father of
conditioning.
The experimenter starts with a stimulus (the unconditioned
stimulus) that will reliably elicit a specific response (the
unconditioned response).
Pavlov’s research-the unconditioned stimulus was meat
powder and the unconditioned response was salivation.
What was to become the conditioned stimulus could be any
of great variety of stimuli: a bell, a ticking metronome, a
triangle drawn on a large care, and so on…
If this stimulus was presented repeatedly just before the
meat powder, it too came to elicit salivation, the
conditioned response, and it thus became a conditioned
stimulus.
Since the term conditioning came to be applied quite
broadly, this particular kind of conditioning, being first
studied, came to be called classical conditioning.
The terms unconditioned stimulus and conditioned stimulus
may seem a bit odd, considering what they mean.
What is meant is that they mean is unconditional stimulus
(not conditional on any previous training), while the bell (or
whatever stimulus precedes the meat) is a conditional on
having been paired with the meat.
**Emphasizing that although Pavlov’s own studies mostly
used food as the unconditioned stimulus, there was no such
limitation either in his theory or in other research on
Pavlovian conditioning.
Unpleasant (or noxious) stimuli have been used as
unconditioned stimuli as much as have pleasant ones.
**Examples range from disliking a food because eating it
followed by illness, to hating a person who mistreated you,
to being afraid of horses after being thrown by one.
Basic Principles of
Pavlovian Conditioning
The most basic principle of Pavlovian conditioning is that
the more often the conditioned stimulus has been presented
just before the unconditioned stimulus, the greater is the
tendency for the conditioned stimulus to produce the
conditioned response. The resulting change indicates the
acquisition of conditioning.
This change represents two laws of acquisition, one stating
that with more pairings of the conditioned and the
unconditioned stimulus, the probability that a conditioned
response will occur increases, and the other stating that the
size of the conditioned responses increases (in Pavlov’s
research, the number of drops of saliva).
A second basic principle of conditioning is extinction.
Extinction means that after acquisition, the more successive
times the conditioned stimulus is then presented without the
unconditioned stimulus, the weaker the tendency to make the
conditioned response will become. As with acquisition, this
law is really two laws, one stating that the more times in
succession the conditioned stimulus has been presented alone,
the smaller the conditioned response will be, and the other
stating that the more such presentations there have been, the
less often any conditioned response will occur when the
conditioned stimulus is presented. Extinction might thus be
considered simply a process of unlearning the conditioning.
Two other principles of conditioning are very basic. One is
generalization. This means that after conditioning, the dog will
make the conditioned response not only to the exact
conditioned stimulus with which it was trained, but also to the
other stimuli that resemble its.
Another principle is discrimination, which is related to
generalization in much the same way that extinction is to
acquisition. Discrimination requires training with two
conditioned stimuli, one of which is always followed by the
unconditioned stimulus (as in acquisition) an the other never
followed by it (as in extinction). As training continues, there
will be less and less conditioned responding to the one not
followed by the unconditioned stimulus, until eventually there
is none.
Excitation and Inhibition
Pavlov suggested that the laws of conditioning could be
explained by the joint actions of two main processes in the
brain: excitation and inhibition. Excitation is a process of
arousal, one that tends to make responses happen, whereas
inhibition is a process of suppression, one that tends to prevent
responses from occurring. Both therefore operate in
opposition to each other. Of the two, excitation plays a much
greater part in producing conditioning, but inhibition is
needed to explain many of the specific ways in which
conditioning works.
An example of conditioning, in which a bell as the
conditioned stimulus is presented to the dog just before meat
is presented as the unconditioned stimulus. Both of these
stimuli produce excitation in the cerebral cortex of the brain,
each at a particular spot in the cortex appropriate to that
stimulus. Since the food is something important to the dog’s
survival, whereas the bell is a biologically less important
stimulus, the excitation produced by the food is the stronger
of the two.
According to Pavlov, excitation is then drawn from the
location of the cortex where the bell is represented to the
location where the food is represented. This effect occurs, he
said, because of two general tendencies. One is the tendency
for weaker excitation to be drawn toward the location of
stronger excitation. The other is the tendency for excitation
that occurs first to be drawn toward the location of excitation
that occurs slightly later. Each time the bell is presented just
before the food, the excitation from the conditioned stimulus is
drawn to the location of the excitation from the unconditioned
stimulus, and as a result the connection between these two
regions in the cortex gets stronger.
Excitation, Pavlov said, will occur not only at the place of the
cortex appropriate for the conditioned stimulus, but also at
the place where the unconditioned stimulus is represented.
This excitation, in turn, will produce a response similar to the
unconditioned response.
Excitation, he said also has an automatic tendency to
irradiate-that is, to spread out from its original focus in all
directions over the surface of the cortex.
The ideas of Pavlov’s was based on direct physiological
information.
Applications and
Implications
Pavlov believed that the principles of conditioning could be
used to explain a variety of phenomena. He related these
principles to personality, considering that one of the most
fundamental differences among dogs-and among humans-is
the balance between excitation and inhibition. Excitatory
personalities tend toward too much unrestrained activity
(“When in doubt, do something, do anything!”), whereas
inhibitory personalities tend toward unresponsiveness
(When in doubt, the safest thing to do is nothing.”).
Pavlov considered conflict between excitation and inhibition
to be the basis of neurosis.
Consider the case of the dogs that had learned a
discrimination between a circle followed by food and an
ellipse followed by no food. After they had learned, on further
trials the ellipse was gradually changed in shape to resemble
more and more closely a circle, so that it was harder and
harder to make the discrimination, until finally it became
impossible to see any difference between the two stimuli and
the discrimination broke down completely. As a result, the
dogs had both excitatory and inhibitory tendencies toward the
seemingly identical figures, and no way to tell which tendency
was appropriate. Pavlov noted that excitatory dogs would
respond to both stimuli, inhibitory dogs to neither.
This failure to discriminate was not just a calm adoption of the
same response to both stimuli. Rather, the dogs barked, tried
to leave the experimental room, and generally appeared
anxious, frustrated, and upset. These symptoms seemed so
similar to those of humans in difficult conflict situations that
Pavlov labeled the syndrome experimental neurosis.
Interceptive conditioning, in which either the conditioned or
the unconditioned stimulus, or both, is presented directly to one
of the internal organs. The responses that get conditioned by
such interceptive stimulation are also responses of the internal
organs or their blood supplies.
Example-Cold water as the unconditioned stimulus can make
the blood vessels in the wall of the stomach constrict, and this
unconditioned response can then be trained as a conditioned
response to some conditioned stimulus. Such conditioning
brings unconscious bodily processes.
Semantic conditioning, the conditioning of meaning… or
conditioning in which the conditioned stimulus is verbal and
the effect of the conditioning is to modify its meaning for the
learner.
Whereas bells and lights and other such conditioned stimuli
make up a first signaling system, language, Pavlov said,
becomes a second signaling system.
Thorndike’s Early
Connectionism
The idea that pleasure and pain are important determiners of
behavior has a distinguished history in psychology. It forms
the basis of the theory of psychological hedonism that was
developed by the English philosopher Jeremy Bentham in the
eighteenth century and adopted by a number of other British
philosophers. According to this view, we all do those things
that give us pleasure and avoid those that give us pain.
However, it remained for Edward L. Thorndike (1874-1949) to
make a similar, more behavioristic view central to the
psychology of learning.
Thorndike was a pioneer in experimental animal psychology.
Instead of relying on stories about the intelligent feats of this or
that animal, he took animals into the laboratory, presented
them with standardized problems, and made careful
observations of how they solved their problems. “Animal
Intelligence” (1898), his monograph, is still one of the classics in
the field.
His most widely quoted studies involved cats in a problem box.
A hungry cat was confined in a cage with a tempting morsel of
fish outside. The cat could open the door by pulling a loop of
string hanging inside the cage. Usually a cat went through a
long process of walking around, clawing the sides of the cage,
and other responses before it pulled the loop of string and was
able to leave the cage.
On successive tests in the cage, the cats took shorter and
shorter times to pull the string. Even after several experiences
of opening the door by pulling the string, on a given trial a cat
would still spend considerable time in other behavior before
pulling the string. This led Thorndike to conclude that the
cat’s learning to pull the string involved not an “intelligent”
understanding of a relation between string and pulling and
door opening but a gradual “stamping in” of the stimulusresponse connection between seeing the string and pulling it.
At the time Thorndike published these studies, they were
radical in two respects: their careful observation of animal
behavior under controlled conditions and their concern with
the gradual strengthening of responses.
They were Thorndike’s answer to the argument about
whether animals solve problems by reasoning or by instinct.
By neither, said Thorndike, but rather by the gradual
learning of the correct response.
Thorndike’s Basic Ideas
The question on whether what animals and people learn is
connections or cognitions, Thorndike was firmly on the
connectionist side. Some of Thorndike’s views on learning had
changed during the course of his career, one that did not
change was his conviction that what we learn are stimulusresponse bonds. These bonds, in his view, were connections in
the nervous system between incoming stimuli and the
responses that those stimuli produce. He did not use the term
“intervening variables,” but he treated these bonds as
intervening variables in his interpretation of learning. Why
does a given stimulus produce a given response rather than
some other response, or none? Because there is a bond
between that stimulus and that particular response.
The question is “What does learning consist of?” The forming
and strengthening and weakening of these stimulus-response
bonds. His theory is thus a clearly connectionist theory.
The other question-”What part does reinforcement play in the
formation of these bonds?” Thorndike was again clear: it
plays a crucial role. His primary law of learning was the law
of effect. This law states that in order for a stimulus-response
bond to be formed or s strengthened, the response must occur
in the presence of the stimulus and then be followed quickly
by a satisfier (reinforcer). In other words, making that
response in the presence of that stimulus must have a
satisfying effect; hence the name, law of effect.
Likewise, if the response occurs in the presence of the stimulus
but is followed by an annoyer, the stimulus-response bond will
be weakened. The fact that satisfiers and annoyers are
essential elements in the learning process, according to
Thorndike, make his, in addition to being a connectionist
theory, a reinforcement theory as well.
Thorndike’s emphasis here was heavily on what the cats did,
rather than on what they thought or felt, in other words, on
their behavior. His use of the terms satisfier and annoyer may
seem too subjective for such an objective approach. However
he defined those two words in a quite objective way.
“By satisfying state of affairs is meant one which the animal
does nothing to avoid, often doing things which maintain or
renew it. By an annoying state of affairs is meant one which
the animal does nothing to preserve, often doing things which
put an end to it”-Thorndike
Thorndike says nothing here about the animal’s feelings, only
about what the animal does. If satisfiers give the animal
pleasure or annoyers give it displeasure, that is not part of
Thorndike’s theory, which defines satisfiers and annoyers by
their effects on the animal’s behavior, not on its feelings.
Later on, Thorndike modified the law of effect to make
satisfiers much more important than annoyers. Reward, he
decided, strengthens connections, but punishment does not
directly weaken them. If punishment is effective in
weakening the tendency to do something, it is primarily
because it makes behavior more variable and thus gives some
new response a chance to be rewarded. He based this change
in interpretation on a variety of animal and human research,
including analysis of biographical information. Thorndike’s
view that reward strengthens behavior directly whereas
punishment weakens it indirectly has been accepted by a
number of subsequent psychologists.
Elaborations
Thorndike believed firmly throughout his career that the
strengthening of stimulus-response bonds by satisfiers is
central in all learning. When he began his research with
animals, he regarded the sort of trial-and-error learning
described above as only one of several possibilities. From
consulting with various experts on animal training, he expected
that his cats would learn faster to pull the loop of string if he
held the cat’s paw in his hand, moved it so that it pulled the
loop of string down, and thus showed the cat that the door of
the cage would then open and let the cat out to where the food
was.
However, his research eventually convinced him that neither of
these methods would work, that animals would learn only by
trying various responses, being reinforced for only one of
them, and thereby gradually learning the successful response.
Though subsequent researchers have had some success with
the other two methods-passive movement and imitation-the
question of how widely they occur when the experiment is done
appropriately is still being argued.
In Thorndike’s career, he stated a number of laws of learning,
of which the law of effect is by far his best known. One of the
others was the law of exercise, which stated that a stimulusresponse bond was strengthening from the addition of
reinforcement.
To the extent that this law of exercise was valid, then the law of
effect would refer only to the additional strengthening from the
addition of reinforcement. However, his research suggested that
any strengthening of a bond by practice alone, without
reinforcement, was quite small. The law of exercise thus
became less important in his theory, overshadowed by the law
of effect. Nevertheless, it retained some importance as a factor
in memory, where repeatedly saying two words together would
strengthen the tendency to remember one when hearing the
other, even without any obvious satisfier following it. Thus
Thorndike, though he stated and enthusiastically advocated the
law of effect, did not completely rule out learning in the absence
of reinforcement.
Thorndike’s concern with education led him to take
considerable interest in the topic of transfer, the effect of
learning one thing on subsequently learning something else.
Usually the transfer is positive, meaning that the second
learning is more rapid than it would be without the first
learning, though sometimes the first learning interferes with
and slow down the second, which constitutes negative transfer.
In Thorndike’s time it was widely believed that certain
difficult subjects learned in school-Latin and math were
favorite examples-produced positive transfer to a wide variety
of other learning, much as though they were strengthening the
brain by exercising it, or at least teaching the student to think
logically in some very general way.
The truth or falsity of this belief was obviously important to
educators and Thorndike set out to test it. He concluded that
learning any material transfers to learning any other material
only the degree that the two overlap. Thorndike’s considerable
influence in educational circles thus came out in favor of
teaching students the specific knowledge and skills they would
need, rather than other knowledge and skills designed to
produce general mental improvement.
Comparison of Thorndike
with Pavlov
•Both set out to study learning in an objective, scientific way.
•Both analyzed not only learning but all behavior into
responses to stimuli.
•Both put a good deal of emphasis on studies of animals, but
were nonetheless strongly concerned with applying what they
learned to the betterment of humankind.
•They were also marked similarities in the laws of learning
that they proposed.
•Both saw gradual strengthening of stimulus-response
connections.
•Both noted that when this reinforcement was removed, the
learned response was extinguished.
Their systems differed in at least two ways. One is the type of
learning on which they focused. In Pavlovian conditioning, a
new stimulus (the conditioned stimulus) comes to elicit a
response that is very similar to the one already elicited by the
unconditioned stimulus…a new stimulus comes to elicit an old
response.
For Thorndike’s cats, the new behavior of pulling the loop of
string was learned as a response to the same stimuli of the
puzzle box that had been there all along-an old stimulus
became attached to a new response.
Pavlov considered it of major importance to figure out what
was happening in the cerebral cortex during conditioning.
Thorndike was little concerned with the underlying physiology.
He assumed that stimulus-response bonds represented some
reality in the nervous system, but it did not matter to him what
in particular was going on in the brain as these bonds were
strengthened and weakened. This distinction is not
particularly important.
Both Pavlov and Thorndike were using intervening variables
inferred from behavior, and their value lies in how adequately
they explained the behavior.
Thorndike’s Place in
Psychology
Thorndike was a man of great energy and of wide interests
within psychology. He was a pioneer not only in both animal
and human learning but also in the psychology of education and
of individual differences. In all of these areas he was interested
both in pure science and in applications, and his contributions
included methods, theory, and data. There are thus a number of
aspects of American psychology for which a look at Thorndike’s
work makes a reasonable starting point. Instead what he did
most effectively for the development of learning theory was to
provide a few strong, simple ideas for subsequent psychologists
and educators to use, build on, or in some cases reject.
For well over half of the century since he published his 1898
monograph on animal learning, the majority of American
learning theorists have followed his lead, making Thorndike’s
pioneering ideas more precise.