プロ家庭教師による記憶理論の講座で、パブロフの条件反射の解説です。彼の書籍をインターネットで読めるようにまとめています。
日本語データ
パブロフ・イワン・ペトローヴィチ (1849-1936)
条件反射：大脳半球の生理的活動の探求 (1927)
ウェブ版編集：矢部祐司(2019)
英語データ
Pavlov, Ivan Petrovich, 1849-1936
Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex (1927)
Translated from Russian into English by G. V. Anrep (1927)
An internet resource developed by Yuji Yabe
プロ家庭教師による難関中学・難関高校・難関大学合格対策カリキュラムを指導依頼できます。
Ｑ：パブロフ博士の本名は何ですか？
Ａ：パブロフ博士の本名は、パブロフ・イワン・ペトローヴィチといい、ロシア出身の科学者です。ロシア人として初めてノーベル賞を受賞されました。
Ｑ：パブロフ博士の問題意識
Ａ：当時の心理学が内観に依存している点を問題にし、生理学の実験により脳の働きを科学的に解明すべきと考えました。身体の他の部位とは異なり、脳は特別に扱われていて、脳の働きをどのように測定するべきか科学的な研究手法を探求しました。
Ｑ：パブロフ博士の研究手法
Ａ：ロシアに実験施設を建てて、犬を用いた動物実験を開始しました。外部からの刺激がどのように犬の脳を刺激して、犬に唾液を催させるかを測定しました。その結果、刺激と反射についての理論をまとめました。パブロフ博士による犬の動物実験は、人々に衝撃を与えたので、パブロフの犬といえば条件反射の代名詞となっています。
Ｑ：パブロフ博士の実験は、どのような内容なのですか？
Ａ：パブロフ博士は、生物への刺激を２種類に分けました。
１つめは無条件刺激(unconditioned stimilus)と呼ばれます。無条件刺激は、生物にあらかじめ備わっている固有の反射を促します。例えば、餌という刺激は、犬に唾液分泌という反射を促します。痛みという刺激は、犬に筋肉の緊張という反射を促します。無条件刺激に対応する反射を、無条件反射(unconditioned reflex)と呼びます。
２つめは、条件刺激(conditioned stimilus)です。条件刺激は、特定の反射とは結びついていません。例えば、ベルの音を聞かせても、唾液分泌は促されません。ところが、条件刺激のベルを鳴らした後に、無条件刺激の餌を見せて、無条件反射の唾液分泌を促していくと、犬に変化が起こります。それまでベルの音を聞かせても、唾液分泌しなかった犬が、ベルの音を聞くだけで、唾液分泌するようになります。もともとは無関係だったベルの音(条件刺激)と唾液分泌(無条件反射)が結びつくことを、条件付(conditioning)と呼びます。
このような条件付の法則をパブロフ博士は発見し、細部をていねいに確認していきました。
Ｑ：パブロフ博士の実験は、どこで実施されたのですか？
Ａ：ロシアのペトログラード(サンクトペテルブルグの別名)にある実験施設です。刺激を厳密に管理するために、専用の建物が用意されました。
Ｑ：パブロフ博士の実験は、それまでの実験とどのように異なるのですか？
Ａ：パブロフ博士の実験は、学習に科学的な根拠を求めました。人間が学習できることは、伝統的に肯定されていましたが、学習の仕組みは科学的に解明されていませんでした。
Ｑ：パブロフ博士の実験は、どのような意義があるのですか？
Ａ：パブロフ博士は、刺激と反射の関係を、人工的に操作できることを実証しました。刺激と反射に秩序を与えることが、学習理論として確立しました。私たちが文字を見て、意味を読み取ることができるのも、刺激と反射の理論に基礎づけられています。
Ｑ：パブロフ博士の条件反射理論は、現代にどのように役立つのですか？
Ａ：パブロフ博士の条件反射理論は、現代では、記憶力の強化を通じて、学習能力向上に役立ちます。他にも、メディア依存対策や広告報道への批判能力となります。条件反射理論によれば、広告による条件刺激は、負の学習とも考えられます。パブロフ博士の確立した理論は、何を記憶するべきか主体的に考えるべきと、私たちに教えてくれます。
Ｑ：パブロフ博士の理論には、どのような限界があるのですか？
Ａ：パブロフ博士の理論の限界は、反射がそのまま理解や記憶とはならなかった点です。
例えば、現代社会では、子供に芸能人の顔(刺激)を見せると、反射が起きます。しかし子供は、芸能人の制度について理解していませんし、芸能人の名前すら覚えていない場合があります。芸能人の顔という刺激に、反射が起きたとしても、刺激がどのようなものか、理解しているわけではありません。
同じように、人間の言葉の刺激に対して、オウムは反射を返すこと(オウム返し)ができますが、オウムが人間の言語を理解しているとは言えません。
このように、反射・記憶・理解には、内容的な差異が指摘できます。現代の試験問題も、反射(択一)・記憶(一問一答)・理解(論述)は、異なる能力として扱います。パブロフの条件反射理論は、小学生から中学生くらいまでの暗記中心カリキュラムまでは有効と考えられます。
テレビ視聴と学力の相関関係も、単純な刺激と反射だけでは、学習が成立しないであろうと示唆しています。
Ｑ：パブロフ博士の実験は、どのような刺激を採用したのですか？
Ａ：実験の刺激として以下を採用しています。しかし、人間に反射を促すものであれば、すべてが条件刺激となりえると述べています。
視覚：ドッグフード・特定の人間・光線
味覚：塩酸・食べられない固形物
嗅覚：バニラ
聴覚：メトロノームの音・特定のヘルツの音・ブザー・車の警笛
触覚：電流・傷
Ｑ：パブロフ博士の実験で、刺激の順番を前後させると、どうなるのですか？
Ａ：パブロフ博士の実験は、無条件刺激(メトロノーム音)の後に、条件刺激(ドッグフード)を提示しました。この場合は、条件付が成功しています。しかし、無条件刺激(ドッグフード)の後に条件刺激(メトロノーム音)を提示すると、条件付は成功しませんでした。このことから、広告は先に覚えさせたい刺激(スポンサー名)を提示して、その後に無条件刺激(強い色や光)を提示するように、制作されています。
Ｑ：パブロフ博士の実験で、刺激の間隔は重要なのですか？
Ａ：刺激の間隔は、条件付に重要です。基本的には、条件刺激のすぐ後に無条件刺激を提示しないと、条件付が起きにくくなります。
Ｑ：パブロフ博士の実験で、条件付の強化とは何ですか？
Ａ：条件付の強化(reinforcement)とは、ひとたび条件付が成立した後で、無条件刺激と条件刺激を再び条件付すると、反射がより強くなることです。いわば、条件付の上乗せができる法則です。この法則は、スポーツやアートの達人が、素晴らしい反応を見せることをよく説明できます。反対に、メディア依存や買物依存も、説明できてしまいます。
Ｑ：パブロフ博士の実験で、無条件刺激と条件刺激では、反射の強さは異なるのですか？
Ａ：条件刺激は、無条件刺激よりも、反射が弱くなることがわかっています。
Ｑ：パブロフ博士の実験で、先行条件付とは何ですか？
Ａ：先行条件付(forward conditioning)とは、条件刺激が無条件刺激より先行する条件付です。
Ｑ：パブロフ博士の実験で、延滞条件付とは何ですか？
Ａ：延滞条件付(delayed conditioning)とは、条件刺激が無条件刺激より遅れて提示される条件付です。延滞時間には内制止が発生し、睡眠に陥る場合もあります。
Ｑ：パブロフ博士の実験で、痕跡条件付とは何ですか？
Ａ：痕跡条件付(delayed conditioning)とは、条件刺激が無条件刺激より遅れて提示される条件付です。条件刺激と無条件刺激はまったく重ならず、条件刺激の終止した後、時間を隔てて、無条件刺激が提示されます。
Ｑ：パブロフ博士の実験で、外制止とは何ですか？
Ａ：外制止(external inhibition)とは、条件付の途中で、条件刺激以外の刺激を提示すると、条件反射が弱められることです。
Ｑ：パブロフ博士の実験で、内制止とは何ですか？
Ａ：内制止(internal inhibition)とは、動物の体内で自然に条件反射が制止されることです。
Ｑ：パブロフ博士の実験で、条件付の消去とは何ですか？
Ａ：条件付の消去(extinction)とは、条件付が成立した後で、条件刺激だけを提示して、無条件刺激を提示しない(無条件反射を起こさない)ようにすると、条件付が弱まり、やがて消去される法則です。いわば、条件刺激に飽きるという法則です。
ただし、ひとたび消去された条件付でも、完全に存在しなくなったわけではく、身体に保存されていることがわかっています。
Ｑ：パブロフ博士の実験で、脱制止とは何ですか？
A：脱制止(disinhibition)とは、消去の進行中に、条件刺激以外の刺激を提示すると、消去しかけた条件反射が復活することです。
Ｑ：パブロフ博士の実験で、般化とは何ですか？
A：般化(generalization)とは、ある条件刺激に対して条件反射を形成すると、それと似ている刺激に対しても条件反射が生じることです。例えば、１０００ヘルツ音に条件反射が生じると、８００ヘルツ音に対しても条件反射が生じます。
Ｑ：パブロフ博士の実験で、分化条件付とは何ですか？
A：分化条件付(differential conditioning)とは、一方の刺激を条件付し、他方の刺激を消去すると、消去された刺激に般化が及ばなくなることです。
Ｑ：パブロフ博士の実験で、高次条件付とは何ですか？
A：高次条件付(higher order conditioning)とは、条件刺激に対する条件反射が形成されたのち、別の条件刺激に対して次々に条件付することでせう。例えば、音刺激を条件付した後に、さらに音刺激に光刺激を条件付します。
Ｑ：パブロフ博士の実験で、感性前条件付とは何ですか？
A：感性前条件付(sensory pre-conditioning)とは、まだ条件付されていない刺激(中性刺激)同士を、反復して提示した後に、片方を条件刺激として条件付すると、もう片方の刺激にも条件付されることです。
Ｑ：パブロフ博士の実験で、大脳の機能はどのように考えられていたのですか？
A：大脳皮質(cerebral cortex)に結合が起きることで、条件付が生じると考えました。
Ｑ：パブロフ博士の実験で、第一信号とは何ですか？
A：条件反射の第一信号とは、動物にみられる直接経験による条件反射です。
The development of the objective method in investigating the physiological activities of the cerebral hemispheres. -- Concept of Reflex. -- Variety of Reflexes. -- Signal reflexes, the most fundamental physiological characteristic of the hemispheres.
大脳半球への好奇心
The cerebral hemispheres stand out as the crowning achievement in the nervous development of the animal kingdom. These structures in the higher animals are of considerable dimensions and exceedingly complex, being made up in man of millions upon millions of cells -- centres or foci of nervous activity -- varying in size, shape and arrangement, and connected with each other by countless branchings from their individual processes. Such complexity of structure naturally suggests a like complexity of function, which in fact is obvious in the higher animal and in man. Consider the dog, which has been for so many countless ages the servant of man. Think how he may be trained to perform various duties, watching, hunting, etc. We know that this complex behaviour of the animal, undoubtedly involving the highest nervous activity, is mainly associated with the cerebral hemispheres. If we remove the hemispheres in the dog [Goltz [l] and others[2]], the animal becomes not only incapable of performing these duties hut also incapable even of looking after itself. It becomes in fact a helpless invalid, and cannot long survive unless it be carefully tended.
大脳半球の生理学の不在
In man also the highest nervous activity is dependent upon the structural and functional integrity of the cerebral hemispheres. As soon as these structures become damaged and their functions impaired in any way, so man also becomes an invalid. He can no longer proceed with his normal duties, but has to be kept out of the working world of his fellow men. In astounding contrast with the unbounded activity of the cerebral hemispheres stands the meagre content of present-day physiological knowledge concerning them. Up to the year 1870,[p. 2] in fact, there was no physiology of the hemispheres; they seemed to be out of reach of the physiologist. In that year the common physiological methods of stimulation and extirpation were first applied to them [Fritsch and Hitzig (3)]. It was found by these workers that stimulation of certain parts of the cortex of the hemispheres (motor cortex) regularly evoked contractions in definite groups of skeletal muscles: extirpation of these parts of the cortex led to disturbances in the normal functioning of the same groups of muscles. Shortly afterwards it was demonstrated [Ferrier [4], H. Munk [5]] that other areas of the cortex which do not evoke any motor activity in response to stimulation are also functionally differentiated. Extirpation of these areas leads to definite defects in the nervous activity associated with certain receptor organs, such as the retina of the eye, the organ of Corti, and the sensory nerve-endings in the skin. Searching investigations have been made, and still are being made, by numerous workers on this question of localization of function in the cortex. Our knowledge has been increased in precision and filled out in detail, especially as regards the motor area, and has even found useful application in medicine. These investigations, however, did not proceed fundamentally beyond the position established by Fritsch and Hitzig. The important question of the physiological mechanism of the whole higher and complex behaviour of the animal which is -- as Goltz showed -- dependent upon the cerebral hemispheres, was not touched in any of these investigations and formed no part of the current physiological knowledge.
脳科学研究が遅れている理由
When therefore we ask the questions: What do those facts which have up to the present been at the disposal of the physiologist explain with regard to the behaviour of the higher animals? What general scheme of the highest nervous activity can they give? Or what general rules governing this activity can they help us to formulate? -- the modern physiologist finds himself at a loss and can give no satisfactory reply. The problem of the mechanism of this complex structure which is so rich in function has got hidden away in a corner, and this unlimited field, so fertile in possibilities for research, has never been adequately explored.[p.3]
The reason for this is quite simple and clear. These nervous activities have never been regarded from the same point of view as those of other organs, or even other parts of the central nervous system. The activities of the hemispheres have been talked about as some kind of special psychical activity, whose working we feel and apprehend in ourselves, and by analogy suppose to exist in animals. This is an anomaly which has placed the physiologist in an extremely difficult position. On the one hand it would seem that the study of the activities of the cerebral hemispheres, as of the activities of any other part of the organism, should be within the compass of physiology, but on the other hand it happens to have been annexed to the special field of another science-psychology.
研究の方法論 心理学の検討
What attitude then should the physiologist adopt? Perhaps he should first of all study the methods of this science of psychology, and only afterwards hope to study the physiological mechanism of the hemispheres? This involves a serious difficulty. It is logical that in its analysis of the various activities of living matter physiology should base itself on the more advanced and more exact sciences -- physics and chemistry. But if we attempt an approach from this science of psychology to the problem confronting us we shall be building our superstructure on a science which has no claim to exactness as compared even with physiology. In fact it is still open to discussion whether psychology is a natural science, or whether it can be regarded as a science at all.
It is not possible here for me to enter deeply into this question, but I will stay to give one fact which strikes me very forcibly, viz. that even the advocates of psychology do not look upon their science as being in any sense exact. The eminent American psychologist, William James, has in recent years referred to psychology not as a science but as a hope of science. Another striking illustration is provided by Wundt, the celebrated philosopher and psychologist, founder of the so-called experimental method in psychology and himself formerly a physiologist. Just before the War (1913), on the occasion of a discussion in Germany as to the advisability of making separate Chairs of Philosophy and Psychology, Wundt opposed the separation, one of his arguments being the impossibility of fixing a common examination schedule in psychology, since every professor had his own special ideas as to what psychology really was. Such testimony seems to show clearly that psychology cannot yet claim the status of an exact science. [p. 4]
研究の方法論 生理学の検討
If this be the case there is no need for the physiologist to have recourse to psychology. It would be more natural that experimental investigation of the physiological activities of the hemispheres should lay a solid foundation for a future true science of psychology; such a course is more likely to lead to the advancement of this branch of natural science.
The physiologist must thus take his own path, where a trail has already been blazed for him. Three hundred years ago Descartes evolved the idea of the reflex. Starting from the assumption that animals behaved simply as machines, he regarded every activity of the organism as a necessary reaction to some external stimulus, the connection between the stimulus and the response being made through a definite nervous path: and this connection, he stated, was the fundamental purpose of the nervous structures in the animal body. This was the basis on which the study of the nervous system was firmly established. In the eighteenth, nineteenth and twentieth centuries the conception of the reflex was used to the full by physiologists. Working at first only on the lower parts of the central nervous system, they came gradually to study more highly developed parts, until quite recently Magnus,[6] continuing the classical investigations of Sherrington[7] upon the spinal reflexes, has succeeded in demonstrating the reflex nature of all the elementary motor activities of the animal organism. Descartes' conception of the reflex was constantly and fruitfully applied in these studies, but its application has stopped short of the cerebral cortex.
It may be hoped that some of the more complex activities of the body, which are made up by a grouping together of the elementary locomotor activities and which enter into the states referred to in psychological phraseology as "playfulness," "fear," "anger," and so forth, will soon be demonstrated as reflex activities of the subcortical parts of the brain. A bold attempt to apply the idea of the reflex to the activities of the hemispheres was made by the Russian physiologist, I. M. Sechenov, on the basis of the knowledge available in his day of the physiology of the central nervous system. In a pamphlet entitled "Reflexes of the Brain," published in Russian in 1863, he attempted to represent the activities of the cerebral hemispheres as reflex -- that is to say, as determined. [p. 5] Thoughts he regarded as reflexes in which the effector path was inhibited, while great outbursts of passion he regarded as exaggerated reflexes with a wide irradiation of excitation. A similar attempt was made more recently by Ch. Richet,[8] who introduced the conception of the psychic reflex, in which the response following on a given stimulus is supposed to be determined by the association of this stimulus with the traces left in the hemispheres by past stimuli. And generally speaking, recent physiology shows a, tendency to regard the highest activities of the hemispheres as an association of the new excitations at any given time with traces left by old ones (associative memory, training, education by experience).
All this, however, was mere conjecture. The time was ripe for a transition to the experimental analysis of the subject -- an analysis which must be as objective as the analysis in any other branch of natural science. An impetus was given to this transition by the rapidly developing science of comparative physiology, which itself sprang up as a direct result of the Theory of Evolution. In dealing with the lower members of the animal kingdom physiologists were, of necessity, compelled to reject anthropomorphic preconceptions, and to direct all their effort towards the elucidation of the connections between the external stimulus and the resulting response, whether locomotor or other reaction. This led to the development of Loeb's doctrine of Animal Tropisms;[9] to the introduction of a new objective terminology to describe animal reactions [Beer, Bethe and Uexküll[10]]; and finally, it led to the investigation by zoologists, using purely objective methods, of the behaviour of thc lower members of the animal kingdom in response to external stimuli-as for example in the classical researches of Jennings.[11]
アメリカの行動主義の心理学について
Under the influence of these new tendencies in biology, which appealed to the practical bent of the American mind, the American School of Psychologists -- already interested in the comparative study of psychology -- evinced a disposition to subject the highest nervous activities of animals to experimental analysis under various [p. 6] specially devised conditions.
ソーンダイクの動物行動実験
We may fairly regard the treatise by Thorndyke [sic], The Animal Intelligence (1898),[12] as the starting point for systematic investigations of this kind. In these investigations the animal was kept in a box, and food was placed outside the box so that it was visible to the animal. In order to get the food the animal had to open a door, which was fastened by various suitable contrivances in the different experiments. Tables and charts were made showing how quickly and in what manner the animal solved the problems set it. The whole process was understood as being the formation of an association between the visual and tactile stimuli on the one hand and the locomotor apparatus on the other. This method, with its modifications, was subsequently applied by numerous authors to the study of questions relating to the associative ability of various animals.
客観的な実験を求めて
At about the same time as Thorndyke[sic] was engaged on this work, I myself (being then quite ignorant of his researches) was also led to the objective study of the hemispheres, by the following circumstance: In the course of a detailed investigation into the activities of the digestive glands I had to inquire into the so-called psychic secretion of some of the glands, a task which I attempted in conjunction with a collaborator. As a result of this investigation an unqualified conviction of the futility of subjective methods of inquiry was firmly stamped upon my mind. It became clear that the only satisfactory solution of the problem lay in an experimental investigation by strictly objective methods. For this purpose I started to record all the external stimuli falling on the animal at the time its reflex reaction was manifested (in this particular case the secretion of saliva), at the same time recording all changes in the reaction of the animal.
２５年に渡る実験
This was the beginning of these investigations, which have gone on now for twenty-five years-years in which numerous fellow-workers on whom I now look back with tender affection have united with mine in this work their hearts and hands. We have of course passed through many stages, and only gradually has the subject been opened up and the difficulties overcome. At first only a few scattered facts were available, but to-day sufficient material has been gathered together to warrant an attempt to present it in a more or less systematized form. At the present time I am in a [p. 7] position to present you with a physiological interpretation of the activities of the cerebral hemispheres which is, at any rate, more in keeping with the structural and functional complexity of this organ than is the collection of fragmentary, though very important, facts which up to the present have represented all the knowledge of this subject. Work on the lines of purely objective investigation into the highest nervous activities has been conducted in the main in the laboratories under my control, and over a hundred collaborators have taken part.
ロシアとアメリカの科学者の違い
Work on somewhat similar lines to ours has been done by the American psychologists. Up to the present, however, there has been one essential point of difference between the American School and ourselves. Being psychologists, their mode of experimentation, in spite of the fact that they are studying these activities on their external aspect, is mostly psychological -- at any rate so far as the arrangement of problems and their analysis and the formulation of results are concerned. Therefore -- with the exception of a small group of "behaviourists " -- their work cannot be regarded as purely physiological in character. We, having started from physiology, continue to adhere strictly to the physiological point of view, investigating and systematizing the whole subject by physiological methods alone. As regards other physiological laboratories a few only have directed their attention to this subject, and that recently; nor have their investigations extended beyond the limits of a preliminary inquiry.
反射の整理
I shall now turn to the description of our material, first giving as a preliminary an account of the general conception of the reflex, of specific physiological reflexes, and of the so-called "instincts."
デカルトの反射神経
Our starting point has been Descartes' idea of the nervous reflex. This is a genuine scientific conception, since it implies necessity. It may be summed up as follows : An external or internal stimulus falls on some one or other nervous receptor and gives rise to a nervous impulse; this nervous impulse is transmitted along nerve fibres to the central nervous system, and here, on account of existing nervous connections, it gives rise to a fresh impulse which passes along outgoing nerve fibres to the active organ, where it excites a special activity of the cellular structures. Thus a stimulus appears to be connected of necessity with a definite response, as cause with effect. It seems obvious that the whole activity of the organism should conform to definite laws. If the animal were not in exact correspondence with its environment it would, sooner or later, [p. 8]cease to exist. To give a biological example: if, instead of being attracted to food, the animal were repelled by it, or if instead of running from fire the anial threw itself into the fire, then it would quickly perish. The animal must respond to changes in the environment in such a manner that its responsive activity is directed towards the preservation of its existence. This conclusion holds also if we consider the living organism in terms of physical and chemical science. Every material system can exist as an entity only so long as its internal forces, attraction, cohesion, etc., balance the external forces acting upon it. This is true for an ordinary stone just as much as for the most complex chemical substances; and its truth should be recognized also for the animal organism. Being a definite circumscribed material system, it can only continue to exist so long as it is in continuous equilibrium with the forces external to it: so soon as this equilibrium is seriously disturbed the organism will cease to exist as the entity it was. Reflexes are the elemental units in the mechanism of perpetual equilibration. Physiologists have studied and are studying at the present time these numerous machine-like, inevitable reactions of the organism-reflexes existing from the very birth of the animal, and due therefore to the inherent organization of the nervous system.
生理学における反射の研究
Reflexes, like the driving-belts of machines of human design, may be of two kinds-positive and negative, excitatory and inhibitory. Although the investigation of these reflexes by physiologists has been going on now for a long time, it is as yet not nearly finished. Fresh reflexes are continually being discovered. We are ignorant of the properties of those receptor organs for which the effective stimulus arises inside the organism, and the internal reflexes themselves remain a field unexplored. The paths by which nervous impulses are conducted in the central nervous system are for the most·part little known, or not ascertained at all. The mechanism of inhibitions confined within the central nervous system remains quite obscure: we know something only of those inhibitory reflexes which manifest themselves along the inhibitory efferent nerves. Furthermore, the combination and interaction of different reflexes are as yet insufficiently understood. Nevertheless physiologists are succeeding more and more in unravelling the mechanism of these machine-like activities of the organism, and may reasonably be expected to elucidate and control it in the end. [p. 9]
本能は反射に含まれるか
To those reflexes which have long been the subject of physiological investigation, and which concern chiefly the activities of separate organs and tissues, there should be added another group of inborn reflexes. These also take place in the nervous system, and they are the inevitable reactions to perfectly definite stimuli. They have to do with reactions of the organism as a whole, and comprise that general behaviour of the animal which has been termed "instinctive."
ハーバード・スペンサーの本能の議論
Since complete agreement as regards the essential affinity of these reactions to the reflex has not yet been attained, we must discuss this question more fully. We owe to the English philosopher, Herbert Spencer, the suggestion that instinctive reactions are reflexes. Ample evidence was later advanced by zoologists, physiologists, and students of comparative psychology in support of this. I propose here to bring together the various arguments in favour of this view. Between the simplest reflex and the instinct we can find numerous stages of transition, and among these we are puzzled to find any line of demarcation.
生まれたてのヒナの本能
To exemplify this we may take the newly hatched chick. This little creature reacts by pecking to any stimulus that catches the eye, whether it be a real object or only a stain in the surface it is walking upon. In what way shall we say that this differs from the inclining of the head, the closing of the lids, when something flicks past its eyes ? We should call this last a defensive reflex, but the first has been termed a feeding instinct: although in pecking: nothing but an inclination of the head and a movement of the beak occurs.
本能は反射よりも複雑
It has also been maintained that instincts are more complex than reflexes. There are, however, exceedingly complex reflexes which nobody would term instincts.
嘔吐は複雑な反射
We may take vomiting as an example. This is very complex and involves the co-ordination of a large number of muscles (both striped and plain) spread over a large area and usually employed in quite different functions of the organism. It involves also a secretory activity on the part of certain glands which is usually evoked for a quite different purpose.
本能の分析
Again, it has been assumed that the long train of actions involved in certain instinctive activities affords a distinctive point of contrast with the reflex, which is regarded as always being built on a simple scale. By way of example we may take the building of a nest, or of dwellings in general, by animals. A chain of incidents is linked ;:together: material is gathered and carried to the site chosen ; there it is built up and strengthened. To look upon this as reflex we must [p. 10] assume that one reflex initiates the next following -- or, in other words, we must regard it as a chain-reflex. But this linking up of activities is not peculiar to instincts alone. We are familiar with numerous reflexes which most certainly fuse into chains. Thus, for example, if we stimulate an afferent nerve, e.g. the sciatic nerve, a reflex rise of blood pressure occurs; the high pressure in the left ventricle of the heart, and first part of the aorta, serves as the effective stimulus to a second reflex, this time a depressor reflex which has a moderating influence on the first. Again, we may take one of the chain reflexes recently established by Magnus. A cat, even when deprived of its cerebral hemispheres, will in most cases land on its feet when thrown from a height.
猫の本能
How is this managed? When the position of the otolithic organ in space is altered a definite reflex is evoked which brings about a contraction of the muscles in the neck, restoring the animal's head to the normal position. This is the first reflex. With the righting of the head a fresh reflex is evoked, and certain muscles of the trunk and limbs are brought into play, restoring the animal to the standing posture. This is the second reflex.
本能はどのような仕組みか
Some, again, object to the identification of instincts with reflexes on this ground: instincts, they say, frequently depend upon the internal state of an organism. For instance, a bird only builds its nest in the mating season. Or, to take a simpler case, when an animal is satiated with eating, then food has no longer any attraction and the animal leaves off eating. Again, the same is true of the sexual impulse. This depends on the age of the organism, and on the state of the reproductive glands; and a considerable influence is exerted by hormones (the products of the glands of internal secretion). But this dependence cannot be claimed as a peculiar property of "instincts." The intensity of any reflex, indeed its very presence, is dependent on the irritability of the centres, which in turn depends constantly on the physical and chemical properties of the blood (automatic stimulation of centres) and on the interaction of reflexes.
反射はひとつの器官だけに限定されない
Last of all, it is sometimes held that whereas reflexes determine only the activities of single organs and tissues, instincts involve the activity of the organism as a whole. We now know, however, from the recent investigations of Magnus and de Kleijn, that standing, walking and the maintenance of postural balance in general, are all nothing but reflexes. [p. 11]
反射と本能を区別しない
It follow from all this that instincts and reflexes are alike the inevitable responses of the organism to internal and external stimuli, and therefore we have no need to call them by two different terms. Reflex has the better claim of the two, in that it has been used from the very beginning with a strictly scientific connotation.
反射は神経系の基盤
The aggregate of reflexes constitutes the foundation of the nervous activities both of men and of animals. It is therefore of great importance to study in detail all the fundnmental reflexes of the organism.
本能についてはあまりよく分かっていないが文学的・直観的な分類はある
Up to the present, unfortunately, this is far from being accomplished, especially, as I have mentioned before, in the case of those reflexes which have been known vaguely as " instincts." Our knowledge of these latter is very limited and fragmentary. Their classification under such headings as "alimentary," "defensive," "sexual," "parental" and "social" instincts, is thoroughly inadequate. Under each of these heads is assembled often a large number of individual reflexes. Some of these are quite unidentified; some are confused with others; and many are still only partially appreciated. I can demonstrate from my own experience to what extent the subject remains inchoate and full of gaps. In the course of the researches which I shall presently explain; we were completely at a loss on one occasion to find any cause for the peculiar behaviour of an animal. It was evidently a very tractable dog, which soon became very friendly with us. We started off with a very simple experiment. The dog was placed in a stand with loose loops round its legs, but so as to be quite comfortable and free to move a pace or two. Nothing more was done except to present the animal repeatedly with food at intervals of some minutes. It stood quietly enough at first, and ate quite readily, but as time went on it became excited and struggled to get out of the stand, scratching at the floor, gnawing the supports, and so on. This ceaseless muscular exertion was accompanied by breathlessness and continuous salivation, which persisted at every experiment during several weeks, the animal getting worse and worse until it was no longer fitted for our researches. For a long time we remained puzzled over the unusual behaviour of this animal. We tried out experimentally numerous possible interpretations, but though we had had long experience with a great number of dogs in our laboratories we could not work out a satisfactory solution of this strange behaviour, until it occurred to us at last that it might be the expression of a special freedom reflex, and that the dog simply could not remain quiet when it was constrained in the stand. [p. 12]
自由反射
This reflex was overcome by setting off another against it -- the reflex for food. We began to give the dog the whole of its food in the stand. At first the animal ate but little, and lost considerably in weight, but gradually it got to eat more, until at last the whole ration was consumed. At the same time the animal grew quieter during the course of the experiments: the freedom reflex was being inhibited.
It is clear that the freedom reflex is one of the most important reflexes, or, if we use a more general term, reactions, of living
beings. This reflex has even yet to find its final recognition. In James's writings it is not even enumerated among the special human "instincts." But it is clear that if the animal were not provided with a reflex of protest against boundaries set to its freedom, the smallest obstacle in its path would interfere with the proper fulfilment of its natural functions. Some animals as we all know have this freedom reflex to such a degree that when placed in captivity they refuse all food, sicken and die.
探求反射 あれは何？反射
As another example of a reflex which is very much neglected we may refer to what may be called the investigatory reflex. I call it the "What-is-it?" reflex. It is this reflex which brings about the immediate response in man and animals to the slightest changes in the world around them, so that they immediately orientate their appropriate receptor organ in accordance with the perceptible quality in the agent bringing about the change, making full investigation of it. The biological significance of this reflex is obvious. If the animal were not provided with such a reflex its life would hang at every moment by a thread. In man this reflex has been greatly developed with far-reaching results, being represented in its highest form by inquisitiveness -- the parent of that scientific method through which we may hope one day to come to a true orientation in knowledge of the world around us.
抑制性反射についてもまだよく分かっていない
Still less has been done towards the elucidation of the class of negative or inhibitory reflexes (instincts) which are often evoked by any strong stimulus or even by weak stimuli, if unusual. Animal hypnotism, so-called, belongs to this category.
反射を整理分類したい
As the fundamental nervous reactions both of men and of animals are inborn in the form of definite reflexes, I must again emphasize how important it is to compile a complete list comprising all these
reflexes with their adequate classification. For, as will be shown later on, all the remaining nervous functions of the animal organism are based upon these reflexes. Now, although the possession of such [p. 13] reflexes as those just described constitutes the fundamental condition for the natural survival of the animal, they are not in themselves sufficient to ensure a prolonged, stable and normal existence.
大脳を切除した犬
This can be shown in dogs in which the cerebral hemispheres have been removed. Leaving out of account the internal reflexes, such a dog still retains the fundamental external reflexes. It is attracted
by food ; it is repelled by nocuous stimuli; it exhibits the investigatory reflex, raising its head and picking up its ears to sound. In addition it exhibits the freedom reflex, offering a powerful resistance to any restraint. Nevertheless it is wholly incapable of
looking after itself, and if left to itself will very soon die. Evidently something important is missing in its present nervous make-up. What nervous activities can it have lost? It is easily seen that, in this dog, the number of stimuli evoking reflex reaction is
considerably diminished; those remaining are of an elemental generalized nature, and act at a very short range. Consequently the dynamic equilibrium between the inner forces of the animal system and the external forces in its environment has become elemental as compared with the exquisite adaptability of the normal animal, and the simpler balance is obviously inadequate to life.
唾液分泌
Let us return now to the simplest reflex from which our investigations started. If food or some rejectable substance finds its way into the mouth, a secretion of saliva is produced. The purpose of this
secretion is in the case of food to alter it chemically, in the case of a rejectable substance to dilute and wash it out of the mouth. This is an example of a reflex due to the physical and chemical properties of a substance when it comes into contact with the mucous membrane of the mouth and tongue. But, in addition to this, a similar reflex secretion is evoked when these substances are placed at a distance from the dog and the receptor organs affected are only those of smell
and sight. Even the vessel from which the food has been given is sufficient to evoke an alimentary reflex complete in all its details; and, further, the secretion may be provoked even by the sight of the
person who brought the vessel, or by the sound of his footsteps. All these innumerable stimuli falling upon the several finely discriminating distance receptors lose their power forever as soon as the hemispheres are taken from the animal, and those only which have a direct effect on mouth and tongue still retain their power. The great advantage to the organism of a capacity to react to the former stimuli is evident, for it is in virtue of their action that [p. 14] food finding its way into the mouth immediately encounters plenty of moistening saliva, and rejectable substances, often nocuous to the mucous membrane, find a layer of protective saliva already in the mouth which rapidly dilutes and washes them out. Even greater is their importance when they evoke the motor component of the complex reflex of nutrition, i.e. when they act as stimuli to the reflex of seeking food.
防衛反射
Here is another example -- the reflex of self-defence. The strong carnivorous animal preys on weaker animals, and these if they waited to defend themselves until the teeth of the foe were in their flesh
would speedily be exterminated. The case takes on a different aspect when the defence reflex is called into play by the sights and sounds of the enemy's approach. Then the prey has a chance to save itself by hiding or by flight.
How can we describe, in general, this difference in the dynamic balance of life between the normal and the decorticated animal? What is the general mechanism and law of this distinction? It is pretty evident that under natural conditions the normal animal must respond not only to stimuli which themselves bring immediate benefit or harm, but also to other physical or chemical agencies -- waves of sound, light, and the like -- which in themselves only signal the approach of
these stimuli; though it is not the sight and sound of the beast of prey which is in itself harmful to the smaller animal, but its teeth and claws.
刺激と反射はどのような関係でありえるか
Now although the signalling stimuli do play a part in those comparatively simple reflexes we have given as examples, yet this is not the most important point. The essential feature of the highest activity of the central nervous system, with which we are concerned and which in the higher animals most probably belongs entirely to the hemispheres, consists not in the fact that innumerable signalling stimuli do initiate reflex reactions in the animal, but in the fact that under different conditions these same stimuli may initiate quite different reflex reactions; and conversely the same reaction may be initiated by different stimuli.
大脳は刺激と反射を制御する
In the above-mentioned example of the salivary reflex, the signal at one time is one particular vessel, at another time another; under certain conditions one man, under different conditions another -- strictly depending upon which vessel had been used in feeding and which man had brought the vessel and given food to the dog. This evidently makes the machine-like responsive activities of the [p. 15] organism still more precise, and adds to it qualities of yet higher perfection. So infinitely complex, so continuously in flux, are the conditions in the world around, that that complex animal system which is itself in living flux, and that system only, has a chance to establish dynamic equilibrium with the environment. Thus we see that the fundamental and the most general function of the hemispheres is that of reacting to signals presented by innumerable of interchangeable signification.
注記
[1] F. Goltz, "Der Hund ohne Grosshirn," Pflüger's Archiv, V. li. p.
570, 1892.
[2] M. Rothmann, "Der Hund ohne Grosshirn." Neurologischcs
Celtralblatt, V. xxviii. p. 1045, 1909.
[3] Fritsch und E. Hitzig, "Ueber die elektrische Erregbarkeit des
Grosshirns." Arckiv für (Anatomie und) Physiologie, p. 300, 1870.
[4] D. Ferrier, Functions of the Brain, London, 1876.
[5] H. Munk, Ueber die Functionen der Grosskirnrinde, Berlin, 1890 and 1909.
[6] R. Magnus, Körperstellung, Berlin, 1924.
[7] C. S. Sherrington, The Integrative Action of the Nervous System,
London, 1906.
[8] Ch. Richet, Réflexes Psychiques. Réflexes Conditionels.
Automatisme Mental. Pavlov's Jubilee Volume, Petrograd, 1925.
[9] J. Loeb, Studies in General Physiology, Chicago, 1905.
[10] Beer, Bethe und Uexküll, "Vorschläge zu einer objectivirenden
Nomenklatur in der Physiologie des Nervensystems," Biologisches
Centralblatt,V., xix. P. 517, 1899.
[11] H. S. Jennings, The Behavior of Lower Organisms, New York, 1906.
[12] E. L. Thorndyke[sic], The Animal Intelligence, An Experimental
Study of the Associative Processes in Animals, New York, 1898.
解説
evince 明らかにする
contrivance 装置・発明
cerebral hemisphere 大脳半球
excitatory 興奮性
inhibitory 抑制性
tractable 摂食の
nocuous stimuli 有害刺激
inchoate 初期段階
freedom reflex 自由反射
investigatory reflex 探求反射
alimentary reflex 消化反射
hypnotism 催眠
secretion of saliva 唾液の分泌
mucous membrane 粘膜
Technical methods employed in the objective investigation of the
functions of the cerebral hemispheres. -- Response to signals as
reflex action. -- Unconditioned and conditioned reflexes. -- Necessary conditions for the development of conditioned reflexes.
実験の客観性について
In the previous lecture I gave an account of the reasons which led us to adopt, for the investigation of the functions of the cerebral hemispheres, the purely objective method used for investigating the physiological activity of the lower parts of the nervous system. In this manner the investigation of the cerebral hemispheres is brought into line with the investigations conducted in other branches of natural science, and their activities are studied as purely physiological facts, without any need to resort to fantastic speculations as to the existence of any possible subjective state in the animal which may be conjectured on analogy with ourselves.
条件反射が存在する理由
From this point of view the whole nervous activity of the animal must be regarded as based firstly on inborn reflexes. These are regular causal connections between certain definite external stimuli acting on the organism and its necessary reflex reactions. Such inborn reflexes are comparatively few in number, and the stimuli setting them in action act close up, being as a rule the general physical and chemical properties of the common agencies which affect the organism. The inborn reflexes by themselves are inadequate to ensure the continued existence of the organism, especially of the more highly organized animals, which, when deprived of their highest nervous activity, are permanently disabled, and if left to themselves, although retaining all their inborn reflexes, soon cease to exist. The complex conditions of everyday existence require a much more detailed and specialized correlation between the animal and its environment than is afforded by the inborn reflexes alone. This more precise correlation can be established only through the medium of the cerebral hemispheres; and we have found that a great number of all sorts of stimuli always act through the medium of the hemispheres as temporary and interchangeable signals for the comparatively small number of agencies [p. 17] of a general character which determine the inborn reflexes, and that this is the only means by which a most delicate adjustment of the organism to the environment can be established. To this function of the hemispheres we gave the name of " signalization."
実験の方法論
Before passing on to describe the results of our investigation it is necessary to give some account of the purely technical side of the methods employed, and to describe the general way in which the signalizing activity of the hemispheres can be studied. It is obvious that the reflex activity of any effector organ can be chosen for the purpose of this investigation, since signalling stimuli can get linked up with any of the inborn reflexes. But, as was mentioned in the first lecture, the starting point for the present investigation was determined in particular by the study of two reflexes -- the food or "alimentary" reflex, and the "defence" reflex in its mildest form, as observed when a rejectable substance finds its way into the mouth of the animal. As it turned out, these two reflexes proved a fortunate choice in many ways. Indeed, while any strong defence reflex, e.g. against such a stimulus as a powerful electric current, makes the animal extremely restless and excited; and while the sexual reflexes require a special environment -- to say nothing of their periodic character and their dependence upon age -- the alimentary reflex and the mild defence reflex to rejectable substances are normal everyday occurrences.
唾液分泌に限定する理由
It is essential to realize that each of these two reflexes -- the alimentary reflex and the mild defence reflex to rejectable substances -- consists of two distinct components, a motor and a secretory. Firstly the animal exhibits a reflex activity directed towards getting hold of the food and eating it or, in the case of rejectable substances towards getting rid of them out of the mouth; and secondly, in both cases an immediate secretion of saliva occurs, in the case of food, to start the physical and chemical processes of digestion and, in the case of rejectable substances, to wash them out of the mouth. We confined our experiments almost entirely to the secretory component of the reflex: the allied motor reactions were taken into account only where there were special reasons. The secretory reflex presents many important advantages for our purpose. It allows of an extremely accurate measurement of the intensity of reflex activity, since either the number of drops in a given time may be counted or else the saliva may be caused to displace a coloured fluid in a horizontally placed graduated glass tube. It would be much [p. 18] more difficult to obtain the same accuracy of measurement for any motor reflex, especially for such complex motor reactions as accompany reflexes to food or to rejectable substances. Even by using most delicate instruments we should never be able to reach such precision in measuring the intensity of the motor component of the reflexes as can easily be attained with the secretory component. Again, a very important point in favour of the secretory reflexes is the much smaller tendency to interpret them in an anthropomorphic fashion -- i.e. in terms of subjective analogy. Although this seems a trivial consideration from our present standpoint, it was of importance in the earlier stages of our investigation and did undoubtedly influence our choice.
唾液の測定方法
For the purpose of registering the intensity of the salivary reflex all the dogs employed in the experiments are subjected to a preliminary minor operation, which consists in the transplantation of the opening of the salivary duct from its natural place on the mucous membrane of the mouth to the outside skin. For this purpose the terminal portion of the salivary duct is dissected and freed from the surrounding tissue, and the duct, together with a small portion of the mucous membrane surrounding its natural opening, is carried through a suitable incision, to the outside of the cheek in the case of the parotid gland, or under the chin in the case of the submaxillary gland. In this new position the duct is fixed by a few stitches which are removed when the wound has healed. As a result of the operation the saliva now flows to the outside, on to the cheek or chin of the animal, instead of into the mouth, so that the measurement of the secretory activity of the gland is greatly facilitated. It is only necessary for this purpose to adjust a small glass funnel over the opening of thc duct on to the skin, and for this we find a special cement prepared according to a formula of Mendeléev [1] most useful. As an alternative, very suitable and accurate as recording apparatus is a hemispherical bulb which also can be hermetically sealed on to the skin. From the bulb project two tubes, one pointing up and the other pointing down. The latter tube is used for drawing off the saliva which collects during each observation, while the former tube connects by air transmission with a horizontal graduated glass tube filled with coloured fluid. As the saliva flows into the hemispherical bulb the coloured fluid is displaced along the graduated tube, where [p. 19] the amount of secretion can be read off accurately. Further, it is not difficult to fix up an automatic electrically-recording device which will split up the displaced fluid into drops of exactly equal volume and reduce any lag in the movement of the fluid to a minimum.[2]
The formation of conditioned reflexes by means of conditioned and direct stimuli. -- Agencies which can be used as conditioned stimuli. -- Inhibition of conditioned reflexes: external inhibition.
条件反射を結びつける
In the previous cases a conditioned reflex was obtained by linking up the action of a new stimulus with an unconditioned reflex. It is possible, however, to obtain a conditioned reflex less directly, by linking up yet a further stimulus with a conditioned stimulus which is already firmly established. Let us refer again to our experiment with the metronome. The sound of the beats was a conditioned stimulus so firmly and powerfully established as readily to admit of demonstration in face of the large audience present at my lecture. The effect of the metronome even under such unfavourable conditions was complete and precise. With the help of this strong conditioned stimulus it has been found possible to give still another stimulus conditioned properties like the first. For if some new and more or less neutral stimulus is applied in conjunction with the metronome alone -- i.e. not at the same time giving food -- this new stimulus also acquires the character of an alimentary conditioned stimulus [Drs. Zeljony, Foursikov, Frolov].
二次条件反射
Conditioned reflexes established in this manner are termed secondary conditioned reflexes, and I shall bring to your attention certain precautions which must be observed for the successful establishment of reflexes of this order.
通常は１０秒の間隔を開ける
The essential condition is that the new stimulus should be withdrawn some seconds before the primary stimulus is applied. With new stimuli of a medium physiological strength this lapse of time must be not less than ten seconds, while for stronger stimuli the interval must be considerably increased. Any shortening of the indicated minimal interval of time leads to a quite different result, typifying a group of extremely delicate and interesting phenomena in the physiology of the hemispheres, which will be treated in the fifth lecture.
二次条件反射の実験
I shall describe first an experiment conducted by Dr. Frolov illustrating the development of a secondary conditioned reflex: A [p.34] dog has two primary alimentary conditioned stimuli firmly established, one to the sound of a metronome and the other to the buzzing of an electric bell. The appearance of a black square in the dog's line of vision is now used as yet a further stimulus, which is to be given the character of a secondary conditioned stimulus. The black square is held in front of the dog for ten seconds, and after an interval of fifteen seconds the metronome is sounded during 30 seconds. In the table given below the square is presented for the tenth time.
Internal inhibition of conditioned reflexes: (a) Extinction.
抑制性反射
Towards the end of the last lecture I discussed external inhibition of conditioned reflexes, as exhibited in numerous cases of temporary clashing between conditioned reflexes and other extra excitatory processes in the brain, and we saw how this clashing led to weakening, more or less profound, and sometimes even to the disappearance of the conditioned reflexes.
内抑制
In the second type of inhibition, which may be termed internal inhibition, the positive conditioned stimulus itself becomes, under definite conditions, negative or inhibitory; it now evokes in the cells of the cortex a process of inhibition instead of the usual excitation. Conditions favouring the development of conditioned reflexes of the negative or inhibitory type are of frequent occurrence, and these reflexes are met with not less frequently than reflexes of the positive or excitatory type.
外抑制と内抑制
The most striking difference between external and internal inhibition is that, whereas under the conditions described in the preceding lecture external inhibition is produced on the very first application of an extra stimulus, internal inhibition on the other hand always develops progressively, quite often very slowly, and in many cases with difficulty.
内抑制の実験
I shall start by describing that form of internal inhibition which was first encountered in our researches, and shall trace the growth of our present conception of its nature.
Demonstration.-- The following is an example of an experiment illustrating the first group of internal inhibitions.
We are taking for this experiment the same dog that was used in the second lecture for the conditioned reflex to the sound of the metronome. In testing the reflex the metronome is sounded for 30 seconds during which the secretion of saliva is measured in drops, and at the same time the interval between the beginning of the stimulus and the beginning of the salivary secretion is recorded. This interval is customarily called the latent period, although as [p. 49] will be seen later some other term might more usefully have been employed. Stimulation by the metronome is not followed in this particular experiment by feeding, i.e. contrary to our usual routine the conditioned reflex is not reinforced. The stimulus of the metronome is repeated during periods of 30 seconds at intervals of two minutes. The following results are obtained:
Internal inhibition (continued): (b) Conditioned Inhibition.
内制止の二種類 実験消去
The fourth lecture was devoted entirely to the study of the first type of internal inhibition, which was termed experimental extinction. In extinction the positive conditioned stimulus is temporarily transformed into a negative or inhibitory one by the simple method of repeating it several times in succession without reinforcement.
内制止の二種類 分化消去
In the present lecture we shall consider the second type of internal inhibition, which has also been investigated in some detail.
分化制止の実験の解説
The method of experimentation is as follows. A positive conditioned stimulus is firmly established in a dog by means of the usual repetitions with reinforcement. A new stimulus is now occasionally added, and whenever the combination is applied, which may be at intervals sometimes extending to hours or days, it is never accompanied by the unconditioned stimulus. In this way the combination is gradually rendered ineffective, so that the conditioned stimulus when applied in combination with the additional stimulus loses its positive effect, although when applied singly and with constant reinforcement it retains its full powers.
分化制止
We have been accustomed in our investigations to designate this phenomenon by the name of conditioned inhibition, although this cannot be regarded as especially appropriate since the development of experimental extinction also is subject to equally rigid conditions. The use of this term, in fact, can only be justified by historical consideration. Since we were concerned in this case with the participation of an additional stimulus, the whole phenomenon was confused at first with external inhibition. It was only later when its character of internal, as distinct from external, inhibition became firmly established that the prefix "conditioned" was added. As will be shown further on, this form of inhibition might more appropriately have been termed "differential inhibition."
The process of development of conditioned inhibition presents [p. 69] especial interest. While illustrating the varied complexity of the phenomena involved, it demonstrates at the same time the value of the experimental method as providing a satisfactory means for the analysis of this very complexity into simple general principles. For this reason we shall discuss conditioned inhibition in considerable detail.
分化制止の２つの刺激の時間関係
The first point of importance in the establishment of a conditioned inhibition is its dependence on time relations between the applications of the two stimuli in the inhibitory combination. Conditioned inhibition is developed with comparative ease in all those cases where the duration of the positive stimulus overlaps that of the additional stimulus. In our experiments it is usual to start the additional stimulus a few seconds (generally from 3 to 5) before the positive stimulus, but provided there is an overlap it is immaterial whether the commencement of the additional stimulus precedes, coincides with, or even follows by a few seconds, that of the positive stimulus. If, on the other hand, the additional stimulus is removed as soon as the positive stimulus is applied, so that the two stimuli never coincide, the development of the conditioned inhibition may be a matter of considerable difficulty, and accompanied by restlessness and various defence reactions of the animal.
分化制止は１０秒の間隔があると生じない
If, finally, a pause of several seconds is introduced between the termination of the additional stimulus and the beginning of the positive stimulus no inhibition develops at all. On the contrary, in the majority of cases, when this pause reaches a duration of about ten seconds, the additional stimulus itself acquires the properties of a positive stimulus. This has been discussed already as the general method of formation of positive conditioned reflexes of the second order. It is only with exceptionally powerful additional stimuli, such for example as a powerful motor-car hooter, that the pause can be increased to so much as twenty seconds and a conditioned inhibition still be developed. An example from the work of Dr. Frolov will serve to illustrate the latter case :
[p. 100]：原著のｐ100ページ
(p. 200)：参照例がp200ページにあり
[sic] ：原文そのまま 原文の表記に異和感があってもこの表記で正しいという確認のための記号です。ラテン語のsic erat scriptumの省略形です。参考 文法辞典
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