Download INVOLVEMENT OF THE PARTIAL REINFORCEMENT

ACTA NEUROBIOL. EXP. 1979, 39: 383-394
Opening address delivered a t t h e Warsaw Colloquium o n Instrumental
Conditioning and Brain Research
M a y 1979
INVOLVEMENT OF THE PARTIAL REINFORCEMENT PROCEDURE
IN REWARD TRAINING: OPENING ADDRESS
Kazimierz ZIELINSKI
Department of Neurophysiology, Nencki Institute of Experimental Biology
Warsaw, Poland
Abstract. The analysis of the course of reward training presented
in early Konorski and Miller's papers (1933, 1936) indicates that the
appearance of active instrumental responses is related with the introduction of the partially reinforced, excitatory classically conditioned
procedure. It is postulated that the mechanism underlying the effects
of this procedure on the shaping of instrumental responses is similar
to that proposed by Konorski (1967) for the effects of inhibitory classically conditioned stimuli on the performance of the instrumental response.
It Q a great honor and privilege for me to be given the opportunity
to deliver an opening lecture about two events of great importance for
this country and for the world of science: the establishment olf 'the
Nencki Institute of Experimental Biology in 1918, and the publication
of the first of Jerzy Konorski's papers on Type I1 Conditioned Reflexes
in 1928 (9, 10). These two events were intimately related.
For more than a dozen years leaders of the intellectual life in Warsaw,
supported by scientists from other countries who were pupils and
friends of the great Polish physiologist and biochemist, Marceli Nencki,
attempted to create a biological institute in Warsaw. Only after Poland
regained independence, however, were the several biological laboratories existing since 1911 along with their Scientific Council and Directorial Board, finally legalized as the Nenchi Institute of Experimental
Biology. A number of outstanding saientists organized a very efficient
establishment, providing the opportunity to conduct research in physiology, biochemistry, protozoology, hydrobiology, ethology and mathematical statistics (16).
The Institute's library, which counted about 30,000 volumes of books
and periodicals before its total destruction during the second World War,
was the reason for the first contact with the Nencki Institue by J e n y
Konorski and Stefan Miller, students of the Medical Faculty at Warsaw
University. Konorski wrote in his autobiography (4): "Instead of medicine, we read and reread Pavlov and discussed every detail of the
experimental work of his coworkers. Moreover, we found in the library
of the Nencki Institute of Experimental Biology the Russian journals
in which the papers on conditioned reflexes were published" (p. 186).
As a result of their studies, these two young gifted men designed and
started on 1 February, 1928, in the Laboratory of Psychology of the Free
Polish University, experiments on avoidance, punishment, reward, and
omission learning, varieties of conditioned reflexes other than those studied by Pavlov and his pupils. Progress in their studies was amazingly
rapid. The first two papers concerning the properties of Type I1 Conditioned Reflexes were delivered to the Warsaw Branch of the French
Biological Society by the summer of 1928, and after a few months were
published in French in "Comptes Rendus de la SociCte de Biologiae"
(9, 10). Saon after, Konorski and Miller were offered the opportunity
to continue their research in the physiological laboratonies of the Medical Faculty at Warsaw University, and later in the State Psychiatric
H~ospitalin Pruszk6w near Warsaw. Their results from this early period
of research were summarized in a monograph, "The foundation of the
physiological theory of acquired movements", published in Polish in
1933 (16). However, much earlier, in 1928, Konorski and Miller exchanged
letters with Pavlov, who invited the two young scientists to his laboratories in Leningrad. Konorski worked in the Institute of Experimental
Medicine for two years (1931-1933), and Miller for only several months.
The main theme of the research conducted by Konorski during the Leningrad period was aoncerned with the relations between instrumental
and classical oonditioned reflexes. The results obtained were published
in Russian sin the "Transactions of Pavlov's Laboratories" in 1936 (7).
After returning from Leningrad the only place in Poland able to
accept the two visitors to Pavlov's laboratories within its staff was the
Nencki Institute. In contrast to electrophysiology, there was no tradition
of behavioral research in Poland. However, the Nencki Institute had
developed a strong schml of ethology, conducting research on the
adaptive behavior of various species from infusoria to amphibians. The
Institute appreciated the importance of neurophysiological ~esearchfor
biological sciences and consk+ently attempted to inoorporate different
groups of neurophysiol~ogists.In addition, there was no "Sovietophobia"
at the Institute. On the contrary, the Soviet Union's scientific centers
were the most numerous among those with which the Institute exchanged
publications. This aspect was rather important for Konorski's future,
since Konorski and Miller, in both lectures and publications, presented
an impartial picture of the development lof Soviet science as well as the
social changes in that country. And finally, Konorski and Miller returned
from the Institute of Experimental Medicine, where the physiological
section was built by Ivan Pavlov, but biochemical section was organized
by Marceli Nencki during the last decade of his life.
Such were the reasons why J e n y Konorski was able to work at the
Nencki Institute in the Department of Physiology, heated by Professor
Kazirnierz Bidaszewiaz. Thereafter, for 40 years, Professor Konorski was
a member of the Nenckii Institute. He started to organize chambers for
experiments on conditioning, while participating in the investigations
of Liliana Lubiliska on the excitability of penipheral nerves and neuromuscular transmission. When the Physiology Department was destroyed
by artillery fire during the first days of the battle for Warsaw, Konorski, like other members of the Institute, tried b salvage apparatus and
bmks fmm under the wreckage and debris, typing out copies of scientific notes and works still in manuscript, which were then preserved
in various places. All of this work was in vain, becoming lost or destroyed
by enemy actions. Among the materials lost were chapters of the book
prepared by Konorski just before the outbreak {of the war. The book
was eventually published in altered form in 1948 under the title "Conditioned reflexes and neuron organization" (3). However, the many losses
in human life were the heaviest blow to the Institute. Among others
who were killed in action at the front, fell in the Warsaw Uprising
or were murdered by the Nazis, was Stefan Miller, the closest friend
and coworker of Konorski. Tragically, he committed suicide when Nazi
troups entered his flat in the Warsaw Ghetto.
Jerzy Komrski and Liliana Lubihska were able to flee Warsaw, and
after a short period of work at the Bialystok hospital, they ~eceived
an (invitation to Leningrad. From there, they moved to Sukhumi, where
Konorski was offered the position of head of the Physiological Department belonging to the Institute of Experimental Medicine. By the beginning of 1945 Kmorski began his yourney back home. A small group
of the pre-war staff, only six persons, reactivated the Nencki Institute,
first at Mi in 1945 and then in Warsaw since 1954. Konorski organized
a Department of Neurophysiology in the Institute, which he headed until
the end of his life. Although he did not relish administrative duties, he
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Neurobiol. Exp. 6/79
performed many. Since 1946 he' was continously a member of Institute's Board of Directors, and he was the Director of the Institute
from 1968 to 1973. No single important event in the Institute was without
his participation. He actively influenced the development of other d5partments of the Institute. Research on human perception as well as in
neurochemistry were greatly stimulated by him. Today the Nencki Institute numbers 116 scientific workers, and 50 of them were either his
pupils and coworkers o r were trained by close collaborators of Konorski.
This number illustrates the extent of his influence on the present character of our Institute. The journal "Acta Neurobiologiae Expenimentalis",
a continuation of the pre-war journal, "Acta Biobgiae Experimentalis",
a c q u i r d an international range under his guidance. Professor Konorski
was also a leader in the cooperation of Polish neurophysiobgists with
scientists of other countries, and the audience of this conference provides
the best proof of the strehgth of ties between the Nencki Institute and
many leading neurophysiological centers thmughout the world.
Jerzy Konorski was the most distinguished among many prominent
scientists and outstanding persons fostered by the Nencki Institute. He
united talent with industry, intellectual courage with responsibility. All
of us were influenced by his ideas and personality, his arguments in
discussions and by his papers and b k s . All of us know many of his
scientific achievements. Thus, I would like to present only one of them,
and probably the most important, reported for the first time by Miller
and Konorski in 1928 i n the three-page paper, "On a particular form of
conditioned reflex" (10). This paper contains a description of the experimental procedures leading to the formation of the four varieties of
Type I1 Conditioned Reflexes, now usually refered as instrumental reflexes, and their basic differences from the procedures of classically conditioned reflexes. This disoovery was presented and discussed in all
monographs written by Jerzy Konorski.
When we compare this paper with corresponding phrases in his last
book, "Integrative activity of the brain" (4, p. 389), we find a number
of differences in the description of the pnocedures for instrumental eonditioning. These differences reflect changes in the understanding of the
processes underlying these conditioning procedures. I n a brief form they
were summarized by J e n y Konorski within a Postscript to the 1928
paper, when i t was translated and published by Skinner in t'he Journal
of the Experimental Analysis of Behavior (11).
In their early papers Konorski and Miller used not only Pavlovian
terminology, but they also applied the tyrpe of analysis developed by
Pavlov's scientific school. They placed emphasis on the stimulus conditions existing during the formation of instrumental responses. Let us
consider the reward training procedure. Konorski and Miller (11) noted
that an active movement is learned when a compound of two stimuli,
external stimulus (A), presented by the experimenter, and the second
stimulus (B), consisting of "all the sensations generated by a particular
movement such as llifting the leg - that is, a set of muscular, tactile, and
other sensations", is accompanied by the food unconditioned sti~mulus
(R). However, the external stimulus alone, similar to "sensations accompanied this particular movement" without the external stimulus, is not
accompanied by food. In other words, training of the instrumental response by the reward method involves the discrimination of the three
arrangements of stimulus conditions: (i) the external stimulus plus the
pqrioceptive stimulus plus hod, ,(ii) the external stimulus alone, and
(iii) the proprioceptive stimulus alone (A+\B4-R versus A versus B).
After some number of presentations of these three stimulus conditions
to the subject "... the stimulus A will then be capable of provoking by
itself the appearance of the stimulus B - in order to complete the conditioned compound" (p. 187). Appearance of the movement of which the
pmprioception is an element of the conditioned compound is the very
basis of type I1 (instrumental) conditioning.
Pavlov considered the excitatory classically conditioned reflex as an
effect of the association between conditioned and unconditioned stimuli.
After the association between the two stimuli is formed, according Do
Pavlov "the conditioned stimulus is a signal, as if it were a substitution
of the uncond~itionedstimulus" (12, p. 117). In the early Konorski and
Miller writings, the compound consisting of external and proprioceptive
stimuli was considered as a conditioned stimulus for the classically conditioned reflex. Thus, there 'was a basic uniformity between Pavlov's
idea of stimulus substitution and Konorski and Miller's (thoughts of the
active instrumental response as a source of stimulation which is missed
when the passive movement was not elicited. The description of instrumental learning procedures with phrases stressing the complementary
role of the proprioceptive stimuli smoothed over the difference between
the classical and instrumental conditioning procedures. To my mind,
this was one of the reasons responsible for the delay in the acceptance of
the specifity of instrumental reflexes by the Pavlovian school. Careful
reading of the Pavlov's foreword to the Konorski and Miller paper published in Russian in 1936 seems to confirm this supposition (12).
Later experiments conducted by Gbrska, Jankowska, Tarnecki and
others (see 4, p. 467-479) showed "that proprioception of a trained movement does not play kyessential role in type I1 conditioning" and "passive
movement as a rule cannot be instrumentalized" (Konorski in the "Postscript", 11, p. 189).
Konorski's impressions about his relations with Pavlov presented in
his Autobiography (5, p. 195) reflected both admiration and some
reservations caused by Pavlov's pegative attitude toward the specificity
of Type I1 Conditioned Reflexes and calling them "motor oonditioned
reflexes" o r "conditioned reflexes of the motor analyser". However, inspection of the Konorski's bibliography (2) indicates that the titles of
the two next pqpers by Konorski and Miller published before their visit
to Leningrad in 1930 included just these very phrases used to indicate
their own primary views on the nature of instrumental reflexes.
The contemporary reader of the early papers by Konorshi and Miller
has an impression that the authors were too Pavlovian, that their early
readings exerted a stnonger influence on them than their own original
findings. Only in the course of experimental work did their understanding of instrumental conditioning become more refined and exact. Paradoxically, the Leningrad period was extremely important for the
scientific maturation of Konorski as the founder of instrumental conditioned reflexes. There, he used dogs with long training histories in classically
conditioned reflexes, which provided an opportunity to investigate the
interrelations between instrumental and classi~callyconditioned reflexes.
These experiments confirmed the preliminary data obtained i n Warsaw,
showing that conditioned stimuli, which elicited classically conditioned alimentary salivation, exerted an inhibitory effect on instrumental
responses established by the reward procedure (Fig. 1). On the other hand,
conditioned stimuli which inhibited classically conditioned salivation,
as a rule, elicited instrumental responses trained by the reward procedure (6, p. 101-128; 7, p. 139-143 and 165-175; 4, p. 369-375). These
findings demonstrated the basic differences between classically conditioned and instrumental reflexes. Moreover, they directed the further
research of Konorski and his pupils into problems of extinction and
inhibition (see, 15). Data on the interrelations between classically conditioned and instrumental reflexes provided arguments in numerous
discussions with other interpretations of instrumental conditioning. For
instance, they were heavily used in Konorski and Miller's paper published
in The Journal (of General Psychology in 1937 (8) where they discussed
Skinner's paper published by the same journal two years earlier (14).
Our present approach to the distinction between various cmditioning
procedures is based on the analysis of contingencies rather than on stimulus conditions. From this point of view we may distinguish several
different relations among the conditioned stimulus, the conditioned respone and the unconditioned stimulus. In the case of classically conditioned reflexes, the conditioned stimulus signals the definite probability
of the unconditioned stimulus presentation which cannot be changed by
subject's behavior. In typical Pavlovian experiments the excitatory conditioned stimulus is a signal for h d or some oth'er unconditioned stimulus i,nevibably given at the end of its action, and presentation of the
Fig. 1. The effect of classically conditioned stimuli, CS+ (excitatory) and CS- (inhibitory), on instrumental response established in the experimental situation. From
above: a, movements of the hindleg; b, salivation; c, CS presentations. The animal
repeatedly lifts its right hindleg, each movement being reinforced by food. Then
(mark in line c) food is not presented for a few seconds and thereafter CS+ (bell)
is given with the 15-s CS-US interval. The dog momentarily stops performing the
movement, waits for food and salivates copiously. The food is presented, CS+ is
terminated and the instrumental responses are restored. Then again food is not
given for a few seconds, and CS- (metronome, 60 cyclelmin) is presented. The movements are not stopped, but the salivation is much reduced. From Konorski and
Miller (7, p. 141).
inhibitory stimulus is a signal that the unconditioned stimulus will not
be given either during or shortly after its action. In the real world
outside the conditioning chamber, such strict correlations between conditi'oned and unconditioned stilmuli are rather exceptional. Normally,
conditioned stimuli signals the certain probability of an unconditioned
stimulus. Performlance of a specific behavior is necessary for obtaining
an attractive unconditioned stimulus or avoiding an aversive one. When
only one kind of overt behavior, let us say, the leg flexion, is ubserved,
four different relations between the conditioned stimulus, conditioned
response and unconditioned stimulus 'may be expected, and all of them
were investigated and described by Konorski and Miller in their first
experimental paper. In reward training the occurrence of the specific
change of behavior (leg flexion) is a necessary condition for presentation
of the attractive unconditioned stimulus, whereas in omission training
the withholding of this same response during CS action is a condition
for obtaining the attractive US after the CS offset. In avoidance training
the specific change of behavior is a condition for not presentating the
aversive US, and in punishment training the withholding of this very
response d u M g CS action is a condition for nonpresentation of the
aversive US. The "truly random" pseudoconditioning procedure (13),
where CS presentations, US occurrences, and the performance of the CR
are not correlated, provides control conditions for both classical and
instrumental training procedures.
In the consecutive run of conditioning trials, either classical or ifnstrumental, a subject changes its behavior according to the consequences of
this behavior ir. previous trials. Let us limit our analysis to the alimentary situation. When excitatory classically conditioned reflexes are trai-ned, not only copious salivation, but also the targeting (orienting) reflex
to the food bowl beoome the $dominantmodes of behavior. The behavior
of a well trained dog is immediately chsanged after the CS onset: all
gross bodily movement become inhibited and the animal's posture indicates that the dog is ready to get the food that will be presented toward
the end of the CS. During training of inhibitory classically conditioned
reflexes, drowsiness in dogs has been frequently described, and when
a large proportion of inhibitory trials are presented during an experimental session, full sleep may even b e observed. In both varieties of classically conditioned reflexes, a subject learns that its behavior has no
consequences on food presentation.
For successful instrumental learning two conditions have to be fulfilled: (i) the change in behavior chosen by the experimenter as an
instrumental response must be performed with some minimal initial
probability, and (ii) the method employed must provide an opportunity
for the subject to recognize that the specific change in its o m behavior
leads to a change in the probability of the unconditioned stimulus.
It is obvious that only elements of the normal repertoire of an animal's
responses may be used as instrumental movements. The higher the behavior chosen by the experimenter as an instrumental response in the
hierarchy of responses emitted in a given experimental situation, the
easier is the instrumental training. However, responses occurring with
a lower probability provide an opportunity for more detailed analysis
of the increase in their frequency and for discovering the conditions that
lead to stabilization of the instrumental response. For dogs placed on the
Pavlovian stand, the leg flexion has a lower probability of occurrence
than the pressing a bar located near the food-tray for rats in an
operant chamber or a key-pecking response for pigeons. Inspection of
the graphs illustrated in the early Konorski and Miller papers indicates
that the method of training employed in their experiments inevitably
increased the general motor activity of the trained dogs and, among
other bodily movements, the leg flexion was also more frequent.
At early stages of reward training conducted acco~dingto the metod
of Konorski and Miller, the dog is confronted with two kihds of trials:
(i) passive leg flection elicited during the action of the sporadic external
stimulus followed by food presentation, and (ii) action of the same sporadic stimulus without leg flection not followed by the alimentary unconditioned stimulus (6, p. 60-69, 10). Taking into account the discoveries,
obtained by Konorski and his collaborators in the 19501s,that proprioceptive feedback is not necessary for instrumental conditioning, we may
infer that at the beginning of reward training a dog is confronted with
the partially reinforced excitatory, classically conditioned reflex situation. In such a situation the central motor behavior system of a hungry
dog is aroused and the trained anilmal performs various motor responses.
Most often movements located high in the hierarchy of responses are
performed; for instance, another instrumental movement acquired during the previous experimental history of the trained animal (6, p. 66-69).
All unsuccessful behaviors become inhibited, the hierarchy of responses
changes in the process of eliminating inappropriate movements and eventually the required behavior occurs.
The importance of the introduction of the partially reinforced excitatory, classic~allyconditioned reflex situation for the course of reward
training may be inferred from experiments conducted by Konorski in
Leningrad (7, p. 145-187). He showed that during the action of the
sporadic stimulus active leg flexions occur only after the introduction
of trials in which the sporadic stimulus was not followed by food (Fig. 2).
One of these experiments, conducted on dog "Nord", yielded data of
special interest for the present analysis. The motor activity of the dog
had been drastically increased by caffeine injection. Among various
movements, numerous leg flexion responses were performed. Some of
them occurred during the action of the sporadic stimulus and according
to the rules of reward training they were reinforced by food presentation.
However, as seen from Fig. 3, in these circumstances transformation of
the excitatory classically conditioned reflex into the instrumental reflex
did not occur. The general motor excitement which was independent of
the contingencies employed during training did not provide the opportunity for the subject to recognize that performance of the required motor
response had any consequences for presentation of the food reinforcement. Only after the introduction of partial reinforcement was a moderate increase of leg flexion responses in the experimental situation
observed and on this background instrumental training proceeded successfuly.
When Kcmorshi discussed the effects of classically conditioned stimuli
on performance of instrumental responses, his line of thinking was almost
identical to that presented above for the analysis of the early stages of
reward training. In his last monograph (4) he wrote: "... the inhibitory
CS in its early stage of development produces a state which differs
from that pmduced both by the positive CS and by the firmly established
inhibitory CS. Whereas the positive CS produces a pure alimentary re-
Sessions
Fig. 2. The course of reward training
in dog Fingal. Daily sessions from 14
January 1932 are presented. From above: a, active leg flexion in intertrial
intervals; b, active leg flexion during
a noise stimulus reinforced by food; C,
noise presentations not accompanied by
leg flexion or food; 4 noise accompanied by passive leg flexion and food.
Vertical dashed line indicates the introduction of noise presentations not
accompanied by passive leg flexion and
food presentation. From Konorski and
Miller (7, p. 165).
Fig. 3. The course of reward training
in dog Nord. Daily sessions from 19
April 1932 are presented. Before the
4th session, 5 cc of 1% caffein solution
was injected. Beginning with the 6th session, noise presentations not accompanied by passive leg flection and food
presentation were introduced. From the
9th session noise of a higher inteaity was
used as a conditioned stimulus. Denotations as in Fig. 2. From Konorski and
Miller (7, p. 176).
spome resembling that elicited by the US itself, and the well-established
inhibitory CS produces the inhibitory response, the early inhibitory CS
given rise to a conflict between the two, resulting in an entirely new
state" (p. 375).
This state is assumed to be the increase of the hunger drive, which
in turn causes the rise of excitability of the central motor behavior system activating structures responsible for the performance of motor acts
most probable in a given situation. An analysis of the early papers by
Konorski and Miller suggests that the some mechanism, i.e., the increase
of the hunger drive and the excitation of the central motor behavioral.
system - is active during instrumental reward training at this stage
when classically conditioned stimuli are partially reinforced with food
presentation.
There are data showing that the increase in the fear drive together
with the excitability of the central motor system accompanies the early
stages of avoidance training. Experiments by Gibson (1) were especially
illustr,ative. Goats and sheep were trained m
i n a large box enabling observation of the animals' behavior. During classically defensive conditioning,
subjects emitted various motor responses, changing their repertoire in
each consecutive trial. Similar behavi'or was observed at early stages of
avoidance training, although, the response pattern chosen by the experimenter as an instrumental response soon became dominant. When the
situation was changed i'n such a way that manother motor response was
now required for successful avoidance of shock, the rise in excitability
of the motor system resulted in increased emission of various motor responses came initially, similar to behavior observed during classically
defensive conditioning.
All of these data indicate that the behavior of animals is subjected
to many changes according to the c,ontingencies employed. Not only during instrumental but also during classical training, changes in the pattern
of motor responses occurred. These processes may be overlooked when
our attention is directed to only one special class of responses. But once
we recognize that our aim is to investigate the integrative activity of the
brain and its role in ad,aptive behavior of humans and animals, we
will probably share Klonorski's opinion offered in his "Postscript" to the
first experimental paper by Miller and Ksonorski (11): "Fi'nally, the sharp
distinction between, not only the procedural side of type I and type I1
conditioned reflexes, but also between their physi~logic~al
mech~anisms
seems to 'me now largely exaggerated. In fact, further investigation shows
with i'ncreasing clarity that both types can be explained on the basis
of the same general principles of connectionistic pmesses" (p. 189).
Over the years the scientific interests of Jerzy Konorski became much
broader than at the beginning of his scientific career. New lines of research were undertaken and more precise methods were introduced. However, the main problem of the present conference, the central mechanisms of instrumental conditioning, always was the most exciting for
him. Professor Konorski presented results of experiments and defended
his ideas to many audiences, listened attentively to others opinions and
lively discussed new f a d s and hypotheses. I am sure that the present
conference will be both interesting and enjoyable, if we try to emulate
the way so typical of Jerzy Konorski, the founder of investigations on
inskumential conditioning.
REFERENCES
1. GIBSON, E. J. 1952. The role of shock in reinforcement. J. Comp. Physiol.
Psychol. 45: 18-30.
2. GLOWACKA, R. 1974. Bibliography of Professor Jerzy Konorski's papers. Acta
Neurobiol. Exp. 34: 681-695.
3. KONORSKI, J. 1948. Conditioned reflexes and neuron organization. Univ. Press,
Cambridge, 267 p.
4. KONORSKI, J. 1967. Integrative activity of the brain: An interdisciplinary
approach. Univ. Chicago Press, Chicago, 531 p.
5. KONORSKI, J. 1974. Jerzy Konorski, In: A history of psychology in autobiography. Vol. 6. Appleton-Century Crofts, New York.
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8. KONORSKI, J. and MILLER, S. 1937. On two types of conditioned reflexes.
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10. MILLER, S. and KONORSKI, J. 1928. Sur une forme particulikre des rbflexes
conditionnels. C. R. Seanc. Soc. Biol. 99: 1155-1157.
11. MILLER, S, and KONORSKI, J. 1969. On a particular type of conditioned
reflex. J. Exp. Anal. Behav. 12: 187-189 (English transl. of Ref. 10).
12. PAVLOV, I. P. 1936. Foreword to the paper by J. Konorski and S. Miller
(in Russian). Tr. Fiziol. Lab. Akad. I. P. Pavlova 6: 115-118.
13. RESCORLA, R. A. 1967. Pavlovian conditioning and its proper control procedures. Psychol. Rev. 74: 71-80.
14. SKINNER, B. F. 1935. Two types of conditioned reflex and a pseudo type.
J. Gen. Psychol. 12: 66-77.
15. ZIELIRSKI, K. 1979. Extinction, inhibition, and differentiation learning. In
A. Dickinson and R. A. Boakes (ed.), Associative mechanisms in conditioning. L. Erlbaum Ass., Hillsdale, p. 269-293.
16. ZIELIRSKI, K. 1979. Sixty Years of the Nencki Institute of Experimental Biology. The Review of the Polish Acad. of Sci. No 4: 47-74.
Kazimierz ZIELINSKI,Nencki Institute of Experimental Biology, Pasteura 3, 02-093 Warsaw,
Poland.