Ivan Petrovich Pavlov advanced the concept of reinforcement, which provided a physicochemical explanation for learning.
In April, 1903, Ivan Petrovich Pavlov delivered a surprising address to an international medical conference in Madrid. It was thought that the noted Russian physiologist would discuss his research on digestion, but instead he described new investigations into the links between psychic and physiological processes. The focal point of these inquiries was the experience that begins, perpetuates, or eliminates a given kind of behavior. Although Pavlov did not formally name that concept until the following year, he was referring to reinforcement, the key physicochemical event in the learning process.
Physiologists had a general understanding of the structure and functions of the nervous system
Before Pavlov’s work on reinforcement, however, monists lacked a cohesive theory supported by a convincing body of experimental data. They observed animals and drew valuable inferences, and they removed parts of animals’ nervous systems, noted the consequences, and reached conclusions. To gain real insight into learning, however, they required a clear approach combined with ways to measure the physical reactions of healthy subjects. Pavlov provided the solution to both problems.
The quantifying technique that Pavlov used to address learned behavior was an offshoot of his 1889-1897 investigations into the effects of the nervous system on digestion. In that project, which won for him the 1904 Nobel Prize in Physiology or Medicine,
Pavlov’s basic approach to the exploration of brain functions also grew from his experiments on digestion. While monitoring the results of sham feeding (the removal of food from a dog’s slit esophagus after it was swallowed but before it entered the stomach), he observed unexpected gastric secretions. As the vagus nerve (which originates in the medulla oblongata and enervates the abdominal cavity) had been severed during surgery, he concluded that part of the stomach’s neural control lay in the cerebral cortex. This led him to believe that secretions could provide information about higher neural activity. Thus, by 1897, Pavlov possessed a powerful leading idea and a technical procedure that could provide measurable data on the activity of the brain.
He also drew on a number of working assumptions. Pavlov was influenced by I. M. Sechenov, a mechanical reductionist who argued that all behavior can be described in terms of reflexes (motor responses to stimulation), reflexes can be explained entirely in physicochemical terms, and an understanding of complicated human reflex behavior is best approached through the study of simpler animal reflex behavior. Pavlov also knew that Charles Darwin
Finally, information drawn from recent observation sharpened Pavlov’s interest in the study of learned behavior. He closely studied Edward L. Thorndike’s experiments on instrumental conditioning, which required a cat to operate an instrument such as a lever or bobbin in order to escape from a puzzle box. Also, while doing research on the digestive system, he noticed an intriguing occurrence: When the presentation of food to a dog was regularly and closely preceded by an alerting signal, such as approaching footsteps, the signal alone caused salivation. Pavlov directed preliminary investigations into that type of behavior (the conditional reflex) as early as 1897.
In 1902, Pavlov applied himself completely to the study of the conditional reflex. The outlines of his theory of classical conditioning immediately took shape, for the basic ideas, much of the terminology, and the investigative methods were almost ready to present. Working in the well-equipped physiological laboratory of the St. Petersburg Institute of Experimental Medicine, he issued preliminary findings at Madrid in 1903 and presented formal results of his research in 1905.
Although his evidence was drawn from experiments on dogs, Pavlov extended his conclusions to the human nervous system. He maintained that all animals have an inborn neural capacity (the unconditional reflex) to react to events necessary for survival (the unconditional stimulus). For example, the sight of food normally produced a certain type and amount of salivation in a dog. As long as the dog was allowed to eat food presented to it, the unconditional reflex endured. Eating the proffered food reinforced the unconditional reflex, for the act of eating maintained (excited) a neural association between the unconditional stimulus and the unconditional reflex. When a dog was repeatedly shown food but was not allowed to eat, salivation weakened and eventually disappeared. Pavlov interpreted this to mean that the association between the sight of food and salivation was actually a temporary neural connection that could be broken through lack of reinforcement. On the other hand, an unreinforced (inhibited) connection could be reactivated; resumption of eating overrode inhibition and restored the extinguished link between salivation and the sight of food.
That link could also be redirected. If an unrelated stimulus (for example, the sound made by a bell) immediately preceded the delivery of food over a long enough period, it could provoke salivation. In Pavlovian terminology, the coupling of a conditional stimulus (a bell tone) with an unconditional stimulus (the sight of food) produced a conditional reflex. In other words, the bell tone made the dog think of food and then salivate. Moreover, a dog was able to discriminate between similar types of reinforced and unreinforced food. For example, it would stop salivating at the sight of white bread it was forbidden to eat but continue salivating at the sight of brown bread that was regularly fed to it.
The linchpin of Pavlov’s theory was thus the notion of reinforcement, which held that animals could associate any two occurrences if the first one promptly and reliably predicted the onset of the second. Reinforcement had a clearly adaptive function, for it provided an animal with a wide range of anticipatory responses to its changing environment. Pavlov’s experimental data, composed of precise, replicable measurements of the volume and rate of saliva in response to a variety of timed stimuli, confirmed the importance of that validating mechanism. The presence or absence of reinforcement, which created conditional reflexes and maintained, extinguished, or resurrected both conditional and unconditional reflexes, permitted an animal to modify its behavior on the basis of experience. Learning took place amid the forging and breaking of neural connections in reaction to changing circumstances.
The importance of reinforcement was first recognized in Russia, where it affected the debate between monistic biologists and state-supported subjectivistic psychologists. The split between government and society during the late czarist period worked to Pavlov’s advantage: While state ideology opposed all brands of materialism, including mechanistic reductionalism, private funding allowed Pavlov to expand investigations into reinforcement. For example, in 1911, the Ledentsov Society financed a series of soundproofed chambers, known as the tower of silence, in which he could study the effects of time intervals on the coupling of conditional and unconditional stimuli. His reputation spread rapidly, and by 1914 he headed an influential school of experimental physiology.
The revolutionary period disrupted Pavlov’s work, but after 1921 the Soviet leadership vigorously supported his research for several reasons: Pavlov’s mechanical reductionism was compatible with the materialistic orientation of the new Marxist regime, his doctrine of reinforcement strengthened the arguments of nurture over nature at a time when the government wished to reeducate the citizenry, and the scientific triumphs of the Pavlovian school had propaganda value for socialism. With state sponsorship, Pavlov and his successors directed large research projects on complex aspects of association through reinforcement.
Advances in cybernetics (the comparison of the communication and control systems of human-made devices with those in the nervous systems of animals) caused some Soviet scientists to question the validity of Pavlov’s conclusions. Nevertheless, his school dominated experimental biology, psychology, and cognitive theory in the Soviet Union, and his environmentally based concept of reinforcement undergirded Soviet educational practice.
Largely because of the language barrier, non-Russians were unable to absorb Pavlov’s concept of reinforcement until the 1920’s. European reaction was unenthusiastic; continental investigators tended toward Gestalt psychology, a holistic approach to perception that emphasizes complexity and thus was at odds with reductionism. The British identified largely with Sir Charles Scott Sherrington’s efforts to confine reflex action to the spinal cord.
The Pavlovian concept of reinforcement had a different reception in the United States, where it was compatible with behaviorism, an indigenous tradition opposed to introspection. Pavlov’s definition of reinforcement had to compete with Thorndike’s, however, as Thorndike had put forward a different definition in 1913 while developing his theory of instrumental conditioning. Thorndike defined reinforcement as any action that causes the appearance of an unconditional stimulus (such as pushing a lever to release a food pellet); according to Pavlov, reinforcement always follows the unconditional stimulus. The sharply differing terminology led to widespread confusion, with Pavlovian reinforcement sometimes described accurately, sometimes as the unconditional stimulus, and sometimes as rewards and punishments.
Generally, Americans and Western Europeans admire Pavlov’s meticulous investigations into the conditions effecting reinforcement and associate his original concept with a specific kind of simple learning (classical, or passive, as opposed to Thorndike’s instrumental, or purposeful). Pavlovian reinforcement has constantly combined and recombined with various forms of behaviorism, and some of its aspects have been incorporated into theories of language formation and information processing, but it is only one of many currents affecting the course of Western psychological and cognitive theory.
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Babkin, Boris P. Pavlov: A Biography. Chicago: University of Chicago Press, 1949. An indispensable primary source rich in anecdotal material, this is a fond memoir by a close colleague. Includes otherwise inaccessible personal and professional information on Pavlov. Comprehensive in scope, although poorly organized and somewhat polemical. Sparsely illustrated and includes notes, a bibliography, and an index. -
Frolov, Y. P. Pavlov and His School: The Theory of Conditioned Reflexes. Translated by C. P. Dutt. New York: Oxford University Press, 1937. This key work by a Soviet physician who worked with Pavlov treats Pavlov’s career in a systematic fashion but contains ideologically motivated inaccuracies typical of the Stalinist period. It should be read in conjunction with Babkin’s biography. Contains charts, diagrams, photographs, and an index. -
Gantt, W. Horsley. “Russian Physiology and Pathology.” In Soviet Science, edited by Ruth C. Christman. Washington, D.C.: American Association for the Advancement of Science, 1952. A somewhat dated but still valuable work by one of Pavlov’s American students. Contains interesting information on Pavlov’s attitudes toward contemporary scientists and scientific problems. Presents a somewhat argumentative but solid treatment of Pavlov’s school and its influence on various aspects of Soviet scientific and educational thought. Heavily footnoted. -
Graham, Loren R. Science, Philosophy, and Human Behavior in the Soviet Union. New York: Columbia University Press, 1987. This expanded version of Graham’s Science and Philosophy in the Soviet Union (1972) offers an excellent treatment of Pavlov’s contributions to Russian physiology and psychology. Includes chapters on the nature-nurture debate, biology and human beings, and cybernetics and computers. Lengthy, with notes, an extensive bibliography, and an index. -
Gray, Jeffrey A. Ivan Pavlov. New York: Viking Press, 1979. An excellent biography that draws extensively from Babkin and Frolov (previously cited). Particularly strong on Pavlov’s intellectual background and research methodology. Pavlov’s work is evaluated in the light of physiological and psychological developments of the 1960’s and 1970’s. Includes diagrams, graphs, and an index. -
Martin, Irene, and A. B. Levey. “Learning What Will Happen Next: Conditioning, Evaluation, and Cognitive Processes.” In Cognitive Processes and Pavlovian Conditioning in Humans, edited by Graham Davey. New York: John Wiley & Sons, 1987. An important and provocative essay that discusses the influence of Pavlovian reinforcement on contemporary cognitive theory. Particularly useful for readers interested in information processing. Traces Pavlov’s impact on behaviorism and outlines new directions in research. -
Pavlov, Ivan P. Experimental Psychology, and Other Essays. New York: Philosophical Library, 1957. A useful primary source that includes Pavlov’s autobiography, the 1903 Madrid speech that contained the first public reference to reinforcement, and the 1904 Nobel Prize speech in which Pavlov first outlined the major elements of classical conditioning. Also includes material on Pavlov’s later attempts to apply aspects of reinforcement to human personality disorders. Includes notes but no index. -
Todes, Daniel P. Pavlov’s Physiology Factory: Experiment, Interpretation, Laboratory Enterprise. Baltimore: The Johns Hopkins University Press, 2001. Explores Pavlov’s early work in digestive physiology through the structures and practices of his laboratory, the physiology department of the Institute of Experimental Medicine. Examines Pavlov’s roles as laboratory manager, experimentalist, entrepreneur, and scientific visionary through his scientific notes and correspondence, unpublished memoirs, and laboratory publications. -
Vucinich, Alexander S. Science in Russian Culture, 1861-1917. Stanford, Calif.: Stanford University Press, 1970. Especially useful to readers interested in history. Places Russian science in the cultural and social context of the postemancipation era. Presents Pavlov’s school as part of a wide, uniquely Russian current in experimental biology. Should be read in conjunction with Graham’s book cited above. Includes notes, an extensive bibliography, and an index.
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