Pavlov's conceptualization of learning.

Introductory texts in psychology create the misleading impression that I. P. Pavlov was concerned solely with conditioned reflexes. In fact, influenced by Woodworth's Contemporary Schools of Psychology (1931), Pavlov also became interested in learning. Pavlov proposed a two-factor learning theory according to which all learning was based on association, but conditioning and trial and error learning had specific functions. According to Pavlov, conditioned reflexes were temporary and unstable and therefore more flexible in the interaction of higher organisms with the changing environment. Trial and error learning provided knowledge and was relatively more stable. Scientific discovery was based on facts obtained by trial and error; valid relations were reinforced by experimental results, whereas incorrect relationships were extinguished. Some suggestions are made that would allow authors of introductory texts to describe more informatively the contributions of Pavlov to modern psychology.     

Pavlov’s position toward konorski and miller’s distinction between pavlovian and motor conditioning paradigms

Two Warsaw medical students, Jerzy Konorski and Stefan Miller, having read I. P. Pavlov’s works on conditional reflexes, informed him in a 1928 letter that they had discovered a new type of conditioning. A previously neutral stimulus preceded the passive lifting of a dog’s paw which then was followed by feeding; this stimulus then evoked the spontaneous raising of that paw. Pavlov responded informing them that their conditioning of motor responses expanded his theory of higher nervous activity, but that their conditioning paradigm—that they named CRII—did not differ fundamentally from the Pavlovian conditioning paradigm. The replication of the Warsaw experiment in Pavlov’s laboratory failed to provide unequivocal results. From 1931 to 1933, Konorski, working in Pavlov’s Leningrad laboratory, further explored the parameters of CRII. Pavlov insisted that the conditioning of motor movements differs from the conditioning of other sensory analyzers only in that, on the neural level, the motor analyzer is both afferent, that is, perceptive, and efferent, that is, responsive. Konorski was not convinced, and he subsequently maintained that the two conditioning paradigms were fundamentally different.     

Pavlov's position on the effects of decortication on conditional reflexes.

This paper examined D. Joravsky's (1989) hypothesis that I.P. Pavlov dogmatically refused to acknowledge that classical conditioning can be mediated by subcortical regions of the large cerebral hemispheres. Decortication literature from 1901 to 1936 was reviewed. The early studies available to Pavlov, who died in 1936, showed that decortication does not allow the establishment of new or retaining of old conditional reflexes (CRs). G.P. Zeleny?'s later experiments(1930) suggested that the establishment of primitive CRs in decorticated dogs was possible. Pavlov never denied this possibility but cautioned that Zeleny?'s experiments could have been methodologically flawed. Although Joravsky's original hypothesis on Pavlov's position on the relation between decortication and the establishment of CRs is by and large accepted, it must be stressed that Pavlov's theory of higher nervous activity was primarily concerned with the function of the brain in the higher organism's struggle for existence. Within this context the cortical, rather than subcortical, processes play the decisive role in the organism's adaptation to the changing external environment.     

Pavlov’s position on the effects of decortication on conditional reflexes

This paper examined D. Joravsky’s (1989) hypothesis that I.P. Pavlov dogmatically refused to acknowledge that classical conditioning can be mediated by subcortical regions of the large cerebral hemispheres. Decortication literature from 1901 to 1936 was reviewed. The early studies available to Pavlov, who died in 1936, showed that decortication does not allow the establishment of new or retaining of old conditional reflexes (CRs). G.P. Zelenyi’s later experiments(1930) suggested that the establishment of primitive CRs in decorticated dogs was possible. Pavlov never denied this possibility but cautioned that Zelenyi’s experiments could have been methodologically flawed. Although Joravsky’s original hypothesis on Pavlov’s position on the relation between decortication and the establishment of CRs is by and large accepted, it must be stressed that Pavlov’s theory of higher nervous activity was primarily concerned with the function of the brain in the higher organism’s struggle for existence. Within this context the cortical, rather than subcortical, processes play the decisive role in the organism’s adaptation to the changing external environment.     

The second signal system as conceived by Pavlov and his disciples

Pavlov clearly formulated his ideas on thesecond signal system (specifically, language) in the 1930s. This occurred in conjunction with his interest in interspecies differences and in the study of human neuroses. Pavlov proposed that conditional reflexes signal concrete reality while symbolic-language provides abstractions of reality. Phylogenetically, language emerged in the humans because this form of communication had survival value to the species. Pavlov’s disciples L. A. Orbeli and N. I. Krasnogorskii had considered the ontogenetic development of language. The experimental investigation of A. G. Ivanov-Smolenskii extended Pavlov’s empirical study of the function of language in psychopathology. Notwithstanding a sustained interest in language, Pavlov did not develop a theory of language acquisition based upon the conditioning principle. Pavlov’s conceptualization of language may not have been original, nor did it contribute significantly to modern linguistics. It is now mainly of historical interest. It was, nevertheless, important to the conceptualization of neuroses within the context of the theory of higher nervous activity and it had far-reaching political implications for Soviet psychology in the immediate post-World War II period.     

Movement as a signal during classical conditioning

Analysis of the available data and that of the author disclosed the peculiarities of motor reaction when used as a conditioned stimulus. The author’s data showed that if signal value is attributed to a motor reaction (passive movement or movement evoked by the direct stimulation of the motor cortex), the changes of excitability in the motor cortex representation of the dog’s leg depend on the biological sign of the reinforcing stimulus during classic conditioning. They also remained the same during instrumental conditioning and were opposite in sign, showed increased excitability in the food situation, and decreased excitability in the defense situation. Using the movement as a conditional stimulus, we managed to uncover the commonality between classic and instrumental conditioning. This enabled us to answer questions, discussed by Pavlov and Guthrie, which, it seems to us, had not been convincingly answered during their time.     

The impact of Pavlov on the psychology of learning in English-speaking countries

The translation of Pavlov's lectures (Pavlov, 1927) provided English-speaking psychologists with access to the full scope of Pavlov's research and theoretical ideas. The impact this had on their study of the psychology of learning can be assessed by examining influential books in this area. This reveals that Watson (1924) had been highly effective in promoting the misleading idea that Pavlov was a fellow S-R theorist. This assumption was not questioned by Tolman (1932), Hilgard and Marquis (1940) or by Hull (1943). However, this mistake was not made by Skinner (1938), who also provided the strongest arguments against Pavlov's belief that behavioral effects required explanation in terms of physiological processes. Post-1927 most learning research in the English-speaking countries continued to use instrumental, rather than Pavlovian, conditioning procedures. Nevertheless, many of the issues addressed by this research were ones that Pavlov had been the first to raise, so that his major influence can be seen as that of defining a research program for subsequent students of learning.     

Overshadowing of a stimulus-reinforcer association by an instrumental response

In two experiments, rats were first exposed to pairings of a clicker and food; they were subsequently, in order to measure the effectiveness of the clicker as a conditioned reinforcer, given the opportunity to press a lever which turned the clicker on. For one group of animals the food originally delivered in the presence of the clicker had been contingent on their performance of an instrumental response (running in a running wheel); for a second the contingency between clicker and food had been purely classical. Although the actual correlation between clicker and food was identical for the two groups, the clicker was a less effective conditioned reinforcer for the first group than for the second. In a third experiment, all animals were initially required to run to obtain food in the presence of the clicker, but one group received additional trials on which food was delivered contingent on running in the absence of the clicker. This group showed less tendency to lever press for the clicker than a second group that had received free food on trials when the clicker was not presented. The results of all three experiments suggest that conditioning to the clicker could be overshadowed if the occurrence of food was more reliably predicted by the execution of an instrumental running response; they thus support the view that instrumental conditioning depends on the establishment of an association between response and reinforcer similar to the association between stimulus and reinforcer underlying classical conditioning.     

Schilder and Pavlov's theory of higher nervous activity. A critique and apologia

In the late 1920s, the Viennese psychoanalyst Paul Schilder, after performing a conditioning experiment with human subjects, criticized I. P. Pavlov's concept of "experimental neurosis." Schilder maintained that subjective reports by conditioned human subjects were more informative than the objectively observed behavior of conditioned dogs. In 1932, Pavlov published a rejoinder to Schilder's critique in the Journal of the American Medical Association. Pavlov maintained that Schilder misunderstood the value and implications of the scientific, objective method in the study of experimental neurosis. In 1934, Schilder subjected Pavlov's theory of higher nervous activity to an incisive critique in a 1935 article in Imago. Schilder objected to Pavlov's narrow, reductionist conceptualization of the conditional reflex. Schilder reiterated his view that the psychological, subjective explanation of the conditional reflex is preferable to the physiological, objective explanation, and that the inference of cortical phenomena from experimental findings might be improper. Neither Pavlov nor any of his disciples replied to Schilder. The author provides an apology for the Pavlovian position, suggesting that Schilder was unfamiliar with early and late writings of Pavlov.     

Contextual conditioning and reinstatement of extinguished instrumental responding

In three experiments we studied the relationship between contextual conditioning and the reinstatement of extinguished lever pressing that occurs when noncontingent food is introduced following extinction. In all three experiments the non-contingent food was presented off-baseline (with the response levers not present). On subsequent tests, with the response levers present, animals that had been exposed to food showed more reinstatement of lever pressing than control animals. This finding rules out alternative mechanisms for the reinstated responding that rely on the interaction of non-contingent food and responding, such as superstitious reinforcement or the discriminative after-effects of food. In addition, in each experiment we demonstrated that manipulations known to affect contextual conditioning (signalling the food in Experiment 1, context extinction in Experiment 2, and switching contexts in Experiment 3) reduced the reinstatement. These results are consistent with the claim that contextual conditioning is important in controlling instrumental conditioning and closely parallel findings concerning the reinstatement of Pavlovian responsing following extinction.     

Experimental evidence of the second signaling system of man

After the first principles of the conditional reflexes had been elucidated by Pavlov and his followers, Pavlov named the neurophysiologic entity common to both animals and men thefirst signaling system. He recognized that man has another signaling system,viz., language, and he proposed that it be named thesecond signaling system. Few experimental studies relating to the second signaling system have been done. Only occasional studies of the effects of spoken language on animals and men, or the effects of spoken language upon EEG and other motor activities of men have been reported. In this paper, the author reports experimental investigation of the second signaling system through the classical conditional salivary method in man, and the development of its methodology.     

Pavlov’s conceptualization of unconditional reflexes,or instincts,within the framework of the theory of higher nervous activity

According to I. P. Pavlov’s theory of higher nervous activity, the establishment and dissolution of conditional reflexes enhances the higher organism’s adaptation to the external environment. Pavlov asserted that, ontogenetically, conditional reflexes are based upon innate, unconditional reflexes (UR) or instincts. Pavlov did not distinguish between URs and instincts, but he preferred the former term. Phylogenetically the URs emerged out of well-established conditional reflexes during the development of higher organisms. An outgrowth of the experimental conditioning procedure, developed during the second decade of this century, was the observation and delineation of new URs. While studying human nervous and psychiatric disorders in the 1930s, Pavlov elucidated other URs. Pavlov identified 13 major URs, but he failed to formulate an exhaustive classification scheme of URs.     

Pavlov as a psychologist

American psychologists are informed on Pavlov’s work on conditional reflexes but not on the full development of his theory of higher nervous activity. This article shows that Pavlov’s theory of higher nervous activity dealt with concepts that concerned contemporary psychologists. Pavlov used the conditioning of the salivary reflex for methodological purposes. Pavlov’s theory of higher nervous activity encompassed overt behavior, neural processes, and the conscious experience. The strong Darwinian element of Pavlov’s theory, with its stress on the higher organisms’ adaptation, is described. With regard to learning, Pavlov, at the end of his scholarly career, proposed that although all learning involves the formation of associations, the organism’s adaptation to the environment is established through conditioning, but the accumulation of knowledge is established by trial and error.     

Pavlovvs. Köhler

During the 1920s, I. P. Pavlov’s scholarly interests broadened to consider problem-solving. Distrusting Wolfgang Köhler’s Gestalt explanation of the problemsolving process and its interspecies aspects, Pavlov performed, from 1933 to 1936, a number of experiments, including a replication of Köhler’s building experiment, using chimpanzees as subjects. Confirming Köhler’s findings, Pavlov explained the problemsolving process in terms of unconditional reflexes and the establishment, by Pavlovian conditioning and the Thorndikian method of trial and error, of temporary neural connections identical, on the psychological level, to associations. In contrast to Köhler’s “structural” explanation, Pavlov emphasized the processes of analysis and synthesis. According to Pavlov insight is achieved progressively—as the result of the organism’s problem-solving behavior—contradicting Köhler’s thesis of a sudden subjective reorganization of the environmental situation. Pavlov explained interspecies differences among higher organisms in terms of the range of a species behavior, with the second signal system as the main distinguishing characteristic between human and nonhuman species.     

Pavlov,psychoanalysis, and neuroses

Pavlov’s discovery of experiment neurosis was serendipitous, yet it was made under the influence of Breuer and Freud’s case of Anna O. In 1914, Pavlov’s disciple N. R. Shenger-Krestovnikova, exploring the limits of visual discrimination in dogs, noticed that when the discrimination was difficult, the dogs’ behavior became disorganized. Pavlov drew an analogy between the condition of Shenger-Krestovnikova’s dogs and their disorganized behavior with Anna O.’s situation and her neurotic reaction. Pavlov concluded that he had demonstrated in the laboratory the elements of neurosis in animals and human alike. Schilder’s criticism of his position, his later study of human neuroses in clinical settings, and the views of Janet may have induced Pavlov to differentiate between animal and human neuroses.     

Schilder and Pavlov’s theory of higher nervous activity

In the late 1920s, the Viennese psychoanalyst Paul Schilder, after performing a conditioning experiment with human subjects, criticized I. P. Pavlov’s concept of “experimental neurosis.” Schilder maintained that subjective reports by conditioned human subjects were more informative than the objectively observed behavior of conditioned dogs. In 1932, Pavlov published a rejoinder to Schilder’s critique in theJournal of the American Medical Association. Pavlov maintained that Schilder misunderstood the value and implications of the scientific, objective method in the study of experimental neurosis. In 1934, Schilder subjected Pavlov’s theory of higher nervous activity to an incisive critique in a 1935 article inImago. Schilder objected to Pavlov’s narrow, reductionist conceptualization of the conditional reflex. Schilder reiterated his view that the psychological, subjective explanation of the conditional reflex is preferable to the physiological, objective explanation, and that the inference of cortical phenomena from experimental findings might be improper. Neither Pavlov nor any of his disciples replied to Schilder. The author provides an apology for the Pavlovian position, suggesting that Schilder was unfamiliar with early and late writings of Pavlov.     

Pavlov's view of the inheritance of acquired characteristics as it relates to theses concerning scientific change

Pavlov's position on the inheritance of acquired characteristics was used to test selected theses of Laudan et al. (1986) concerning scientific change. It was determined that, despite negative experimental findings, Pavlov continued to accept the possibility of the inheritance of acquired habits. This confirms the main thesis I that, once accepted, theories persist despite negative experimental evidence. Pavolv's adherence to the concept of inheritance of acquired characteristics might possibly be explained by his early experiences. Adolescent readings of a popularized version of Darwin's theory, which included the concept of inheritance of acquired characteristics, profoundly influenced Pavlov's subsequent intellectual life. Overwhelmed by the theory, as originally presented, Pavlov was unable to alter his views in light of contrary findings.     

Recent Russian Pavloviana

In recent years three books have appeared which contribute greatly to our knowledge of Pavlov’s life and work, and of the development of the laboratory in Leningrad which bears his name and his intellectual imprint. These works are (1) A volume of brief, highly personal comments on I. P. Pavlov (Kreps, 1967); (2) A collection of short biographies, pictures, and selective bibliographies of individuals who had worked with Pavlov (Kvasov and Fedotova-Grot, 1967); and (3) An outline of the history of the I. P. Pavlov Institute of Physiology which grew from a most unprepossessing laboratory, taken over by I. P. Pavlov in 1907, into a giant institution with a staff currently exceeding 1,000 (Lange, 1968).     

Pavloviana inPsychology of the 20th Century: A special review

In the encyclopedicPsychology of the 20th Century three volumes are relevant to the work of I. P. Pavlov, his predecessors, contemporaries, and followers. Volume 1 (1976) provides an extensive account of the history of non-introspective, “objective” psychology. In Volume 4 (1977), examined in this review and consisting of sections on “Theories of Learning” and “Behavior Modification,” separate chapters are devoted to Pavlov’s life and work, and its continuation in the Soviet Union. Classical conditioning is considered in the context of S-R learning theories, interaction with operant conditioning, and development of behavior therapy. Additional materials are likely to be presented in Volume 6 (to be published) dealing with animal psychology, ethology, and physiological psychology.     

Pavlov and the Rockefeller foundation

Despite the tension between the United States and the Soviet Union in the early 1920’s, the Rockefeller Foundation and the Rockefeller Institute for Medical Research found ways to assist I. P. Pavlov. In addition to providing scientific literature and financial aid, these institutions and their officers rendered important moral support to the scientific career of Pavlov during his later years. In 1923, as a guest of the Rockefeller Institute, Pavlov visited American scientific laboratories. In 1924, he requested and received a number of books on physiology, and during the 1930’s the Foundation helped him to acquire equipment for his Leningrad laboratory.