The Story of Psychology (48 page)

Ivan Pavlov (1849–1936), a very different breed of scientist, was a research physiologist who spent the first half of his career investigating the digestive process. It was in the course of this work that he noticed the odd phenomenon of the salivating dog, and he spent the second half of his career studying what he called “conditioned reflexes.”
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From first to last he considered conditioning a physiological rather than a psychological process, and although the laws of conditioning became as basic to behaviorism as the laws of learning and effect, he had so poor an opinion of psychology that he threatened to fire anyone in his laboratory who used psychological terminology. To his dying day he insisted that he was not a psychologist but a physiologist studying brain reflexes.

Pavlov was born in a central Russian farming village. His father was the local Orthodox priest, his mother the daughter of a priest, and Pavlov planned to follow in the family tradition. Czar Alexander II had recently made free education available to gifted but poor students; Pavlov qualified on both counts, and was educated in a primary school and a seminary. But while he was at the seminary he read Darwin’s
Origin of Species
and the Russian physiologist Ivan Sechenov’s
Reflexes of the Brain
, and underwent something akin to a conversion. Abandoning his plans for the priesthood, he quit the seminary to study natural science at the University of Saint Petersburg (again thanks to the Czar’s largesse), where Sechenov was a professor of physiology.

Pavlov graduated in 1875 with a brilliant record and went on to study medicine, but his goal was research, not practice, and he had to support himself—and, after 1881, a wife—on ill-paid assistantships. At that time, Russia offered far fewer opportunities to young scientists than did the Western countries, and despite Pavlov’s extraordinary talent and his impressive research studies in physiology, he could eke out only a marginal existence for many years.

He was too absorbed in his work, however, to be concerned about the exigencies of daily living; he was the embodiment of the impractical intellectual. During his engagement, he spent what little money he had on luxuries for his fiancée and only once bought her something practical: a pair of shoes that she urgently needed for a trip. But when she got to her destination and opened her luggage, she found only one shoe. She wrote to ask what had happened, and he replied, “Don’t look for your shoe. I took it as a remembrance of you and have put it on my desk.”
When they were married and living in near poverty, he often forgot to pick up his monthly salary until his wife reminded him. One winter, when he could afford little fuel for their apartment, a batch of butterflies he kept at home to study metamorphosis succumbed to the cold. When his wife complained about their poverty, he answered, exasperated, “Oh, leave me alone, please. A real misfortune has occurred. All my butterflies have died, and you are worrying about some silly trifle.”

But in the laboratory, Pavlov was practical, perfectionist, and systematic. He expected his assistants to live up to his standards, and castigated or fired those who fell short in any way, whatever the reason. During the Revolution (with which, for many years, he had no sympathy, though eventually he became a supporter of the system), one of his employees arrived late. When Pavlov upbraided him, the man said there had been street fighting en route and he had been in danger of losing his life, but Pavlov angrily replied that that was no excuse and that devotion to science should supersede all other motives. According to some accounts, he sacked the man.

That was long after Pavlov had become successful. In 1891, at the age of forty-two, he was at last appointed professor at the St. Petersburg Military Academy, and a few years later professor at St. Petersburg University. With this solid footing, he was able to organize the Institute of Experimental Medicine, the laboratory in which he conducted his research for forty years. His work during the 1890s was on digestion, which he studied by surgically creating in the stomach of laboratory dogs a little pouch or separate compartment with a fistula implanted in it. This enabled him to observe the gastric reflex (the secretion of gastric juices when the dog began to eat) without the contaminating presence of food. His findings won him a Nobel Prize in medicine in 1904, and in 1907 he reached the height of scientific prestige in Russia when he became an academician, or full member, of the Academy of Sciences.

Sometime between 1897 and 1900, in the course of his gastric-reflex research, Pavlov became aware of an odd and annoying phenomenon: the dogs would secrete gastric juices and saliva at times other than feedings—for instance, when they saw or heard their keeper shortly before a regular mealtime. At first Pavlov regarded this as a nuisance, since it interfered with the data on the quantities of digestive secretions. But he recognized that there must be an explanation for the production of such fluids when there was no food in the dog’s mouth or even nearby. An obvious one was that the dog “realized” that mealtime was near and these thoughts produced the secretions, but the resolutely antipsychological
Pavlov would have nothing to do with such subjective speculations.

Though reluctant to do research on the matter, he finally decided he could look into it, since in his opinion it was an entirely physiological phenomenon—a “psychical secretion” due to a reflex in the brain caused by the stimulus of the sight or sound of the person who usually brought food. In 1902 he began to study how and when such a stimulus, inherently unconnected to the glandular response, was capable of causing it, and he spent the rest of his life investigating the phenomenon.

Although Pavlov was an expert surgeon, he spared himself the labor of creating stomach pouches for this research. Since the dogs produced saliva as well as gastric juices at the sight of their keepers, it was enough to implant a simple fistula in one of the salivary glands and hook this up to a collecting and recording device. The dogs were trained to stand still on a table, and were praised, petted, and fed for doing so. Eager to please, they would jump onto the table without being told to and patiently remain there, loosely harnessed in place and attached to equipment. The harness was necessary to prevent disruption of the apparatus, a rubber tube connecting the fistula to a collecting vessel and a recording drum. The dogs faced a wall with a window in it; directly in front of them, inside the experimental chamber, was a bowl into which food could be mechanically dropped.

As soon as a dog had food in its mouth, its saliva began to flow; since this was a response that required no training, Pavlov called the food an “unconditioned stimulus” and the salivary response an “unconditioned reflex.” The matter to be studied, however, was the link between a neutral stimulus and the same reflex. Typically, the experimenter, out of sight so as not to be a signal to the dog, would make a sound—ring a bell, buzz a buzzer—and would cause food to drop into the bowl anywhere from five to thirty seconds later. At first, the sound of the bell or buzzer would produce only a normal reflex—the pricking-up of the dog’s ears—but no salivary response. But after a number of these sequences, the sound alone would cause the dog’s saliva to start flowing. In Pavlov’s terms, the sound had become a “conditioned stimulus” to salivation, which had become a “conditioned reflex” to the sound.

Pavlov and his assistants ran many variations of this experiment. Instead of a sound, they would flash a light or rotate an object the dog could see through the window, manipulate apparatus that touched the dog or tugged on a part of its harness, change the length of time between the neutral stimulus and the delivery of food, and so on. In all cases,
neutral stimuli could be made into conditioned ones, but with varying degrees of ease; a neutral odor (not of food) might require twenty or more pairings to become a conditioned stimulus, while the rotation of an object in the dog’s view might take only five pairings, the sounding of a loud buzzer only one.
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A psychologist would have called the conditioning process associative learning, but Pavlov explained it in physiological terms. Acknowledging indebtedness to his mentor, Sechenov, and to Descartes, the first to offer a reflex theory, he theorized that an unconditioned response, such as salivating on taking food into the mouth, was a brain reflex: A direct connection existed between the sensory and motor nerves in the spine or lower brain centers. In contrast, a conditioned response, such as salivating at the sound of a bell or other formerly neutral stimulus, was the result of new reflexive pathways created by the conditioning process in the cortex of the brain.

Pavlov developed this theory of localized brain reflexes in great detail to fit his findings about conditioning. But it was largely ignored except in the Soviet Union, and in America was soon conclusively disproven by the psychologist Karl Lashley, who removed different areas and amounts of cortex from rats, then had them learn mazes, and found that their loss of ability to learn was related not to the destruction of any particular cortical area but to the total amount destroyed.
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The fate of Pavlov’s physiological theory, however, in no way diminished the enthusiastic acceptance of his laboratory data and laws of conditioning as a major addition to psychological knowledge. These were some of his more noteworthy findings:

Timing:
The sequence of the stimuli is critical. Only if the neutral stimulus precedes the unconditioned reflex does it become a conditioned stimulus, capable of eliciting the reflex. In one experiment, an assistant gave a dog food and five to ten seconds later turned on a loud buzzer; even after 374 such pairings, the buzzer alone did not bring about salivation. When he sounded the buzzer
before
giving the dog food, a single pairing was enough to make it a conditioned stimulus.
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Extinction:
Unlike an unconditioned reflex to an unconditioned stimulus, the connection between a conditioned stimulus and a conditioned reflex is impermanent. If the conditioned stimulus is repeatedly presented without reinforcement (food), the salivary response weakens and eventually disappears.

Generalization:
If a dog was presented with a stimulus similar to, but somewhat different from, a stimulus it had become conditioned to—for instance, a tone higher or lower than the one paired with food—the dog would salivate, but less strongly than in response to the conditioned tone. The greater the difference between tones, or between any conditioned stimulus and a related stimulus, the weaker the response. The dog was, in effect, generalizing from its experience and expecting similar experiences to yield similar results.

Differentiation:
After a dog had been conditioned to salivate on hearing a given tone and also on hearing another tone some notes lower, if the first tone was then always reinforced by food but the second one never was, the dog would gradually cease to salivate in response to the second tone. The dog had learned to “differentiate”—the term more often used by English and American psychologists is “discriminate”—between the stimuli.

Experimental neurosis:
In seeking to determine the limits of his dogs’ ability to discriminate, Pavlov unexpectedly precipitated in them something resembling a nervous breakdown. In one historic study, a dog learned to discriminate between a circle flashed on a screen, always followed by food, and an elongated ellipse flashed on the screen, never followed by food. When the dog’s salivating at the sight of the circle and failure to salivate at the sight of the ellipse were well established, the assistant began changing the shape of the ellipse, making it ever more nearly circular. The dog kept learning to discriminate between the circle and the rounder ellipses until the ratio of the axes of the ellipse was 7:8. The assistant then tried an even rounder ellipse whose axes had a ratio of 8:9, but at that point, Pavlov later wrote,

Only after long rest and careful treatment did the dog recover enough to tolerate experiments in easier differentiations.

286 The Story of Psychology

Pavlov believed that he had identified the fundamental unit of learning in animals and human beings. All learned behavior, he said, whether acquired in school or outside it, was nothing but “a long chain of conditioned reflexes” whose acquisition, maintenance, and extinction were governed by the laws he and his assistants had discovered. His ideas profoundly influenced Russian psychology from early in the century until the 1950s, but in the West remained largely unknown for some years, even though Pavlov had mentioned conditioning in his 1904 Nobel award address.

In 1908 Robert Yerkes (who would later direct the development of the Army Alpha and Beta) and a colleague learned about Pavlov’s work from German journals, corresponded with him, and published a brief article in the
Psychological Bulletin
describing his method and main findings. They emphasized the usefulness of his research methods but failed to predict the effect the concept of the conditioned reflex would have on American psychology.
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But in 1916 John B. Watson—whom we are about to meet—began to spell out how Pavlovian conditioning enlarged the behaviorist theory of psychology, and a few years later he termed the conditioned reflex “the keystone of the arch” of behaviorist theory and methodology.
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In

1927 Pavlov’s book,
Conditioned Reflexes
, appeared in English, and from then on behaviorist psychologists rapidly absorbed his ideas and borrowed his research methods. The number of articles on Pavlovian conditioning published in psychological and medical journals increased geometrically from the mid-1920s on, totaling nearly a thousand by 1943.
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In 1951, Professor Henry Garrett of Columbia University summed up the impact of Pavlovian ideas on experimental psychology, which had been largely behaviorist for more than three decades: