Download 20 IVAN PAVLOV AND CLASSICAL CONDITIONING

20
IVAN PAVLOV
AND CLASSICAL
CONDITIONING
Ivan Pavlov was not a psychologist. He was a physiologist, and one of the most
prestigious scientists in the world even before his discovery of classical, or Pavlovian, conditioning.
Ivan Petrovich Pavlov (1849-1936) was born in Ryazan in central Russia, where
his father was a village priest. He was educated first at the church school in Ryazan
and then at the theological seminary there. But he decided to become a scientist,
and in 1870 he enrolled in the natural science curriculum. During his first year
thereafter, he conducted an experiment on the physiology of the pancreatic nerves
that won him a gold medal.
He went on to study at the Academy of Medical Surgery, where he completed
his studies (winning another gold medal for research on circulation) in 1883. In
1890 Pavlov was invited to organize and direct the Department of Physiology at
the Institute of Experimental Medicine, where he remained. This institute became
one of the most important research centers in the world, and here Pavlov did the
research on the physiology of digestion that won him the Nobel Prize in 1904.
From this work also came his accidental discovery of conditioned reflexes, which he
saw as a way of investigating the higher functions of the brain.
Pavlov was passionate about his science. According to George Miller, "During
the [Russian] revolution he scolded one of his assistants for arriving ten minutes
late for an experiment; shooting and fighting in the streets should not interfere
when there was research to be done in the laboratory" (1962, pp. 179-180). He
could not have been an easy man to work with. Yet his clear sense of what was right
extended beyond his high scientific standards. In 1927, when the sons of priests
were expelled from the medical schools by the Soviet government, he resigned as a
professor of physiology, saying, "I am the son of a priest and if you expel the others,
I will go, too" (p. 185).
Pavlov's interest was in how the nervous system works. Such a big question cannot be researched all at once, so Pavlov narrowed his thinking down to the study of
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salivary secretions. When an assistant placed food in a dog's mouth, Pavlov would
collect saliva (through a tube into the mouth), and measure the amount of salivation that occurred in response to the food under various conditions.
However, a difficulty soon arose. After a while, the dog would begin to salivate as
the assistant approached, before any food was placed in its mouth. Clearly that was a
problem. Pavlov wanted to study salivation as a response to food in the mouth. He
could hardly do that if salivation begins when there is no food in the mouth.
Pavlov decided, however, that what was happening here was even more interesting than the original question. Pavlov realized that he was watching the brain
form a new connection, or pathway. The sight of the assistant, who brought food,
had become connected in the brain with the arrival of the food itself. Salivation
occurred in anticipation of that food.
Pavlov set out to study the formation of such connections. But the assistant was
an unnecessary complication, and the dog had had experience with him before.
Pavlov wanted to study the formation of a brand-new association, from the beginning. Therefore, he would begin his experiments with a "signal" that, at the start,
had no association at all with food. He would sound the clicks of a metronome (or it
could be any of a number of stimuli, such as the famous bell). A very brief time after
that, he would place some food in the dog's mouth, by way of a pneumatic system
that would blow a measured amount of food directly into its mouth. (That way,
there was no approach of an assistant to complicate things.)
After a few such pairings, what is called classical or Pavlovian conditioning occurs.
Salivation now begins to occur to the metronome alone. (This can be shown by
occasional test trials in which the food is omitted. Or, if the signal comes first by a
brief period, we may see salivation in response to the signal before the food comes.)
The salivary response has become a conditioned response or conditioned reflex.
Pavlov and his assistants went on to explore the effects of varying the kind of
signal used. It could, it seemed, be almost anything that the dog could detect-a
bell, the sound of a metronome, a light going on, a light going off, and so on. He
could study the effect of varying the interval between the signal for food and the
food itself, the effects of presenting the signal without the food (experimental extinction), and much more. Meanwhile other researchers, following Pavlov's lead, were
extending the findings to other reflexes and other species, humans included.
Human salivary conditioning, in fact, is quite easy to demonstrate. Salivation can
be measured by weighing a small wad of cotton (the kind that dentists use), placing
it in the subject's mouth, removing it after a carefully timed period, and weighing
it again. The gain in weight shows how much saliva has been produced. But the
response can be something quite other than salivation. A puff of air delivered to the
corner of the eye will trigger a reflex blink. If the puff is signaled by some neutral
stimulus such as a tone, after a while the blink will begin to occur as a conditioned
response to the tone alone, before the puff of air occurs. Or the change in skin conductance that accompanies a state of emotion or arousal-the galvanic skin response,
or GSR-might be measured. That too can be conditioned to a light, or a tone, or a
picture of a particular person-any signal, presumably, can be used in this way.
All these findings, varied as they were, fit into a rather simple framework, shown
in figure 20.1. Begin with some signal or stimulus-the unconditioned stimulus, or
UCS-which already triggers some reflex reaction. The response is the unconditioned response, or UCR. These can be any of a number of specific things-food in
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Ivan Pavlov and Classical Conditioning
Figure 20.1
Pavlovian or classical conditioning
A.
B.
UCS
CSUCS
C ._
UCR
. . . >UCR
CS*CR
the mouth that evokes salivation, a puff of air on the eye that evokes a blink, a mild
shock to the finger that elicits finger withdrawal, and so on . That signal is paired
with another signal that initially does not trigger the response in question. This is
the conditioned stimulus, or CS . It too can be different in different experiments : it
might be a tone, the sound of a ticking metronome, a light going on, a light going
off, or a touch on the skin-again, any of these will do . After a number of such pairings, we will begin to see the original response, the UCR, occurring in response
to the CS alone . When that happens, we call it a conditioned response or conditioned
reflex (CR) .
Thus, figure 20 .1 shows a summary picture of many such experiments in many
species . Present any CS along with any UCS, many times, and we will see a "connection" forming, so that the CS comes to trigger the response (now a CR) on a
greater and greater proportion of the trials .
Now, that conception of conditioning is too simple, and has had to be modified
since Pavlov's day. Some reasons for this are discussed elsewhere (chapter 24) . But
the basic idea is still with us, and it extends far beyond saliva, and far beyond dogs .
First-and Pavlov made much of this-every variable in his conditioning experiments was objective. The tone, the food, the salivary flow-all are events that anyone can see and measure . For many centuries, philosophers had been talking about
associations between one idea and another "in the mind" (chapter 2) . But "ideas"
are in the mind, locked up inside each person or animal where no one else can
see them . In Pavlov's work, the association was between a stimulus and a response
that anyone could observe . Anyone who doubted Pavlov's findings could repeat
the experiments and see for him or herself . It is true that Ebbinghaus (chapter 29),
a little earlier, had shown ways in which associations could be studied objectively
in humans . But Pavlov showed how they could be studied objectively in any species . It's also true that the connection in the brain is hypothetical ; we do not see it
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directly. But more modern methods of studying the brain have brought scientists
much closer to seeing it directly, so that they can investigate how it works. Such
research is still in progress today.
Apart from the question of how it takes place, the underlying principles of conditioning could shed some light on a number of real-life concerns, not just in dogs,
and not just about salivation. Conditioning may well play a role in some of the
attitudes we form. If a person has an emotional reaction (negative or positive) to
members of certain groups, might this be a conditioned emotional reaction, occurring as a conditioned response to the mention of the group or to the presence of
members of it?
Conditioning may play a role in the fears we acquire, and it might help explain
the individuality and idiosyncrasy of these. One dog may salivate (or blink) at the
occurrence of a tone, whereas another dog may ignore the tone but salivate (or
blink) when a light goes off. The same response occurs to different stimuli in the
two cases. This can be understood if the two dogs have different conditioning histories-that is, if salivation (or blinking) has been conditioned as a response to the
tone in the one case, and to the light in the other.
Human behavior may include parallel cases. Perhaps John is afraid of dogs;
James is not, but he is afraid of speaking before a group. The same response (fear)
is evoked by different stimuli or situations. This too might result from differences
in conditioning histories. Maybe James had been laughed at a number of times
while giving an oral presentation, and perhaps the bad feelings associated with this
became conditioned responses triggered by public-speaking situations. John may
have had painful experiences with a dog. Or perhaps he has seen someone else react
fearfully to dogs, and has picked up a conditioned fear reaction that way. Since
Pavlov's time, we have learned that this sort of vicarious conditioning can and does
occur.
Finally, if conditioning may play a role in the development of certain fears, it
may also be used to eliminate them. In other words, it may be used as a therapeutic
procedure (chapter 26).
Thus the concepts and methods of Pavlovian conditioning, have very wide ramifications indeed. They may help explain some otherwise puzzling facets of human
behavior.
BIBLIOGRAPHY
Babkin, B. P. (1949). Pavlov: A biography. Chicago: University of Chicago Press.
Boring, E. G. (1950). A history of experimental psychology (2nd ed.). New York: Appleton-Century-Crofts.
Bower, G. H., & Hilgard, E. R. (1981). Theories of learning (5th ed.). Englewood Cliffs, NJ:
Prentice-Hall.
Miller, G. A. (1962). Psychology: The science of mental life. New York: Harper & Row.
Pavlov, I. P. (1927). Conditioned reflexes: An investigation of the physiological activity of the cerebral
cortex ( G. V Anrep, Trans.). London: Oxford University Press, Humphrey Milford.
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