QUESTIONS1. How old is the science of psychology?2. What do you know about its early growth?3. What are the difficulties besetting psychology?4. What is the origin of popular psychology?5. Why is psychology so much hampered by prejudice?6. State the two ways in which psychology has been influenced by natural science.7. How was psychology influenced by medieval theology?8. Who were the opponents of theological psychology?9. What does freedom of action mean?10. What kind of ignorance is the cause of the belief in absolute freedom?11. How did the associational psychology originate?12. What is meant by the faculty psychology?13. What does psychology owe to Herbart?14. What is voluntarism?15. Why are mechanical explanations of mental life inadequate?16. From which science can psychology obtain the most fruitful analogies?17. Which science gave in the earlier part of the nineteenth century the strongest direct impulse to psychology?18. What is psychophysics and who is its author?19. What is meant by the personal equation?20. What experimental investigations were suggested by the personal equation?21. How did the study of the physiology of the brain influence psychology?22. Is psychology a special science?
QUESTIONS
1. How old is the science of psychology?
2. What do you know about its early growth?
3. What are the difficulties besetting psychology?
4. What is the origin of popular psychology?
5. Why is psychology so much hampered by prejudice?
6. State the two ways in which psychology has been influenced by natural science.
7. How was psychology influenced by medieval theology?
8. Who were the opponents of theological psychology?
9. What does freedom of action mean?
10. What kind of ignorance is the cause of the belief in absolute freedom?
11. How did the associational psychology originate?
12. What is meant by the faculty psychology?
13. What does psychology owe to Herbart?
14. What is voluntarism?
15. Why are mechanical explanations of mental life inadequate?
16. From which science can psychology obtain the most fruitful analogies?
17. Which science gave in the earlier part of the nineteenth century the strongest direct impulse to psychology?
18. What is psychophysics and who is its author?
19. What is meant by the personal equation?
20. What experimental investigations were suggested by the personal equation?
21. How did the study of the physiology of the brain influence psychology?
22. Is psychology a special science?
Aswe all know, the processes of our mental life stand in the closest relationship with the functions of the nervous system, especially with the functions of its highest organ, the brain. Local anemia, that is, a lack of blood in the brain, causes fainting, a cessation of consciousness; on the other hand, during mental work the blood pressure in the brain is higher than usual and metabolism is increased. Narcotic or poisonous drugs, as alcohol, caffein, and morphine, which influence mental activity, do this by means of their effect on the nervous system. Aside from such experiences, there are two special groups of facts upon which our knowledge of this relationship is based.
First the dependence of mental development on the development of the nervous system. This is most conspicuous when man and animals are compared. It is somewhat obscured, however, by the relation of the size of the brain to the size of the animal. The larger animal has as a rule the larger brain. Therefore the brain of man can be compared only with the brain of such animals as are of nearly the same size. When such a comparison is made, man is found to be no less superior in nervous organization than in intelligence. His brain is about three times as heavy, absolutely and relatively, as that of the animals most nearly approaching him, the anthropoid apes; eight to ten times as heavy asthe brain of the most intelligent animals lower down in the scale, for instance large dogs. Similar relations between brain weight and intelligence are found in the human race itself. Of course, we cannot expect that this relation will always be found in a comparison of only two individuals. The conditions are too complex for such a regularity to exist; but it is easily demonstrated when averages of groups of intelligent and unintelligent men are compared. We do not expect, either, that in every individual case physical strength is exactly proportional to the weight of the muscles, although no one doubts that strength depends on the weight of the muscles.
The second of the facts upon which our knowledge of the relationship between mental life and nervous function is based, consists in the parallel effects of disturbances of their normal condition. Diseases or injuries of the brain are, as a rule, accompanied by disturbances of the mental life. On the other hand, mental disturbances can often be traced to lesions or structural modifications in the brain. This cannot be done in every case; but the actual connection is none the less certain. It is often very difficult to decide whether or not any mental abnormality exists. Expert psychiatrists have for weeks at a time observed men suspected of mental disease without being able to pronounce judgment. Equally difficult is the discovery of material changes in the brain and its elements. Much progress has been made in recent times in this respect; but it is still far from easy to recognize the more delicate changes in nervous structure resulting from disease. Certain abnormalities may never become directly visible although they involve disturbances of function, for instance, abnormalities in the nutrition of the nervous elements or changes in their normal sensitivity. No wonder, then,that for many mental diseases, as hysteria, corresponding material lesions are not yet known. But the correctness of our thesis is so strongly secured by the enormous number of cases in which it has been demonstrated, that no one doubts that it applies also to those cases in which, often for good reasons, its demonstration has thus far been impossible.
Of much importance is the particular form of this relationship between brain function and mental life. Popular thought attributes the chief classes of total mental activity to special parts of the brain. Judgment is thought to have its seat behind the thinker’s high forehead. The occipital part of the brain is, according to the medieval philosophers, the organ of memory. And so Gall’s phrenology met with ready acceptance from the public at large, which was delighted to learn that musical ability, mathematical talent, religious sentiment, egotism and altruism, and many other character traits had their special organs in the brain. But anatomists and physiologists have not been able to admit the plausibility of this doctrine.
Yet popular thought has, on the other hand, always emphasized the unity of mind. Those who regard its unity as the chief characteristic of mind have for centuries sought for the single point in the brain where the mind can be said to have its seat. If it were distributed all through the brain, would it not be possible to cut the mind into pieces by simply cutting the brain?
That both these views of the relation between brain and mind are inadmissible has become certain. Since about forty years ago the truth in this matter has been known. But to understand it clearly it is necessary first to familiarize ourselves with the construction of the nervous system.
QUESTIONS23. What do we learn from a comparison of brain weight and intelligence?24. What is the relation between nervous pathology and mental abnormality?25. Is phrenology admissible?26. What view concerning the relation of brain and mind is suggested by the unity of mind?
QUESTIONS
23. What do we learn from a comparison of brain weight and intelligence?
24. What is the relation between nervous pathology and mental abnormality?
25. Is phrenology admissible?
26. What view concerning the relation of brain and mind is suggested by the unity of mind?
Fig. 1.—Multipolar Cell Body.Fig. 1.—Multipolar Cell Body.
The number of elements making up the nervous system is estimated at about four thousand millions. It will help us to comprehend the significance of this number if we understand that a man’s life devoted to nothing but counting them would be too short to accomplish this task, for a hundred years contain little more than three thousand million seconds. These elements are stringlike bodies, so thin that they are invisible to the naked eye. They are generally calledneurons. Within them different parts are to be distinguished. The part which is most important for the neuron’s life is a spherical, bobbin-shaped, pyramidal, or starlike body, called the ganglioncell or cell body, located usually near one of the ends of the long fiber of the neuron, but sometimes nearer the middle of the fiber. The length of the fiber varies from a fraction of an inch to several feet. The fiber may be compared with a telephone wire, inasmuch as its function consists in carrying a peculiar kind of excitatory process.
Fig. 2—Pyramidal Cell Body. a, Nerve fiber with collaterals.Fig. 2—Pyramidal Cell Body. a, Nerve fiber with collaterals.
Fig. 3.—Dendrites of a Nerve Cell of the Cerebellum.Fig. 3.—Dendrites of a Nerve Cell of the Cerebellum.
At both ends of the neuron are usually found treelike branches. When the cell body is located near one of the ends of the fiber, many of these branches take their origin from the cell body and give it the pyramidal or starlike appearance illustrated by figures 1, 2, and 4. These branches are called dendrites, from the Greek word for tree,dendron. How wonderfully complicated the branching of a neuron may be is illustrated by figure 3. In addition to the dendrites a neuron possesses another kind of branches, resembling incharacter the tributaries of a large river, entering into it at any point of its course. These are called collaterals (lowest part of figure 2).
Fig. 4.—Various Types of Cell Bodies. 1 and 2, Giant pyramidal cell bodies; n, nerve fiber.Fig. 4.—Various Types of Cell Bodies. 1 and 2, Giant pyramidal cell bodies; n, nerve fiber.
Fig. 5.—Longitudinal Section of a Nerve Fiber with Stained Fibrils. a, Medullated sheath.Fig. 5.—Longitudinal Section of a Nerve Fiber with Stained Fibrils. a, Medullated sheath.
The ganglion cells have a varying internal structure, which may be made visible to the eye when the cells have been stained by the use of different chemicals. They are found to contain small corpuscles with a network of minute fibrils between them, as shown in figures 1 and 4. The nerve fibers, too, in spite of being only1/40to1/500mm. thick, permit us to distinguish smaller parts (fig. 5). The core consists of a bundle of delicate, semi-fluid, parallel fibrils, the axis-cylinder. This is surrounded generally by a fatty, marrow-like sheath, and in the peripheral parts of the system this sheath is again inclosed in a membrane. Certain fibers attain a considerable length, for example, those which end in the fingers and toes, having their origin in the spinal region of the body.
The treelike branches of the main fiber and of the collaterals, if far away from the cell body, are sometimes called the terminal arborization, from the Latin word for tree,arbor(fig. 6). The treelike branching has most probably a functional significance of great importance. It enables the endings of different neurons to come into close enough contact to make it possible for the nervous processes to pass over from one neuron into another neuron, without destroying the individuality, the relative independence of each neuron.
Fig. 6.—Terminal Arborization of Optical Nerve Fibers.Fig. 6.—Terminal Arborization of Optical Nerve Fibers.
Wherever large masses of neurons are accumulated, the location of the ganglion cells can be found directly by the naked eye. The fibers are colorless and somewhat transparent. Where they are massed together, the whole looks whitish, as is the case with snow crystals, or foam. The ganglion cells, however, contain a dark pigment, and where many of them are present among the fibers, the whole mass looks reddish gray. Accordingly one speaks of white matter and gray matter in the nervous system.
The nature of the excitatory process for the carriage of which the neurons exist is still unknown. It is certain, however, that this process is not an electrical phenomenon. Electrical changes accompany the nervous process and enable us to recognize its presence and even to measure it; but they are not identical with the nervous process.Probably it is a kind of chemical process, perhaps analogous to the migration of ions in the electrolyte of a galvanic element, the lost energy being restored by the organism. Two facts are especially noteworthy. The velocity of propagation has been found to be about 60 meters per second in the human nervous system. In the lowest animals propagation is often considerably slower. It is clear, therefore, that it is an altogether different magnitude from the velocities found in light, electricity, or even sound.
A second fact is the summation of weak stimulations. The second one produces a stronger effect than the first, the third again a stronger effect, and so on. It also happens that a number of successive stimuli produce a noticeable effect, whereas one of these stimuli alone, on account of its weakness, would produce none. On the other hand, if strong stimuli succeed one another, the effect becomes less and less conspicuous. The neurons are fatigued, as we say, and require time for recuperation.
The elements of the nervous system just described are combined into one structure according to a surprisingly simple plan, in spite of its seeming complexity. This apparent complexity results chiefly from the enormous number of elements entering into the combination. The purpose of the nervous architecture may be briefly described thus: The conductivity of the nervous tissue is employed tobring all the sensory points of the living organism into close connection with all the motor points, thus making a body capable of unitary action out of a mere accumulation of organs, each of which serves its specific end. Walking along and meeting an obstacle, I must be able first to lookabout and find a way of pushing it aside or climbing over it, and then to push or climb. This is impossible unless my eyes are connected with the muscles of the head, the arms, the legs. Perhaps I am inattentive, or it is dark, so that I run against the obstacle with my feet or my body. In this case it is necessary that the sensory points of my skin be connected with all those muscles. Hearing a call, I must be able to turn my head so that I may hear more distinctly the sound I am expected to perceive; but I must also be able to move my tongue and the rest of my vocal organs in order to answer, or, as the case may require, my arms and legs in order to defend and protect myself. Thus the ear and all other sensory points of the body must be closely connected with all the motor points.
It is plain, then, that the simplest kind of nervous system must consist of three kinds of neurons: sensory (often called afferent), motor (often called efferent), and connecting neurons. To improve the working of such a system, the afferent and the efferent neurons, and especially the connecting (associating) paths, are developed by the introduction of additional neurons, serving to cross-connect the primary chains of neurons.Figure 7illustrates the architecture of an exceedingly simple nervous system of the most rudimentary kind.
A perfection of the system is brought about by a superstructure built on essentially the same plan.Figure 8is a diagram illustrating this. The pointsS´andM´correspond to the points of the same names in figure 7. But several systems (three in the diagram) like that of figure 7 have been combined by connecting neurons in exactly the same manner in which the combination was effected in figure 7. In this higher system (nerve center, we shouldcall it) the pointsS´´´andM´´have a significance comparable to that ofS´andM´.
Fig. 7.—Diagram of Nervous Architecture: Reflex Arches connected by a Low Nerve Center. (From Psychological Review, 15, 1908.)Fig. 7.—Diagram of Nervous Architecture: Reflex Arches connected by a Low Nerve Center.(From Psychological Review, 15, 1908.)
Fig. 8.—Diagram of Nervous Architecture: Lower Nerve Centers connected by a Higher Center. (From Psychological Review, 15, 1908.)Fig. 8.—Diagram of Nervous Architecture: Lower Nerve Centers connected by a Higher Center.(From Psychological Review, 15, 1908.)
Several of these larger systems (three in the diagram) are combined again by means of connecting neurons inexactly the same manner as before. This is illustrated by figure 9. The pointsS´´´andM´´´have a significance like that ofS´andM´,S´´´being nearer to sensory points of the body than to motor points,M´´´being nearer to motor points. This system of connecting neurons represents again what we may call a higher nerve center—higher still than those which are combined in it.
Fig. 9.—Diagram of Nervous Architecture: Higher Nerve Centers connected by a Still Higher Center.Fig. 9.—Diagram of Nervous Architecture: Higher Nerve Centers connected by a Still Higher Center.
Thus we may conceive any number of systems, one still higher than the other. And we may understand how it is possible that simpler mental functions may enter into a combination, forming a unitary new function, without completely losing their individuality as functions of a lower order; for combinations of simple functions represented bydirectconnections into complex functions are brought about only by mediation of higher connecting neurons which represent theless directconnections of sensory and motor points. The most manifold associations are made possible. A practically inexhaustible number of different adaptations is structurally prepared, so that the most complicated circumstances and situations find the organism capable of meeting them in a useful reaction. This type of nervous system is the property of the highest animals andof man. The lower type of nervous system is represented by the reflex arches of the so-called spinal and subcortical centers. The higher type is represented by the cerebrum and cerebellum, which during a process of evolution covering hundreds of thousands of years have gradually been developed to serve as the highest centers of the nervous system.
The most prominent part of the nervous system is that inclosed within the skull and the vertebral column. The spinal cord runs all through this column up to the skull. Entering into the skull, it thickens and forms what is called the bulb (medulla oblongata). It then divides into several bodies, which are referred to as the subcortical centers, because they are located below the cortex, which is the surface layer of the cerebrum, or large brain. These subcortical centers contain the central ends of neurons which are links of chains of afferent neurons coming from the higher sense organs and from the sensory points of the skin and the internal organs. Chains of efferent neurons, on the other hand, take their origin in the subcortical centers, reaching at their peripheral ends the motor points of the body, that is, the muscle fibers of our skeletal muscles and of the muscle tissues contained in the alimentary canal and the other internal organs.
Above and partly surrounding the subcortical centers are the large brain and the cerebellum or small brain. The ganglion cells of the neurons contained in the cerebrum and cerebellum are all located near the surface or cortex. There seems to be a peculiar advantage—not yet perfectly understood—in having the gray matter spread out over the surface of the cerebrum and cerebellum in as thin a layer as possible. To this end the surface of the cerebrum is much increased by the formation of large folds, separatedby deep fissures (see figure 10). In the cerebellum the folds are more numerous and exceedingly fine, and they do not have the appearance of being the product of fissuration. The surface of the cerebrum is estimated to be equal to a square with a side eighteen inches long. Without the fissures the surface would be only about one third of this. The mixture of ganglion cells and fibers making up the gray matter of the brain is illustrated in figures 11 and 12. Both are sections of the cortex of the cerebrum. In figure 11 the cell bodies alone are stained and thus made visible; in figure 12 the fibers alone are stained.
Fig. 10.—Frontal Section of the Right Cerebral Hemisphere.Fig. 10.—Frontal Section of the Right Cerebral Hemisphere.
From what has been said thus far it is clear that certain areas of the cortex must be connected with certain groups
Fig. 11.—Section of the Cerebral Cortex. Only the cell bodies are stained.Fig. 11.—Section of the Cerebral Cortex.Only the cell bodies are stained.Fig. 12.—Section of the Cerebral Cortex.Only the fibers are stained.
of sensory points or motor points of the body much more directly than with others. This is confirmed by histological, pathological, and experimental investigations. For the eyes and the ears, for the muscles of arms and legs, hands and feet, even the several fingers and toes, the corresponding areas of the cortex—that is, the areas with which there is direct connection—are definitely known.Figure 13conveys an idea of the relation between certain parts of the brain and the sensory and motor organs of the body.
Fig. 13.—Localization of Peripheral Functions in the Cerebral Cortex.Fig. 13.—Localization of Peripheral Functions in the Cerebral Cortex.
We have already touched on the question as to the relation between the nervous system and consciousness. It is evident that no single point of the nervous system can be regarded as the long-searched-for seat of the soul, since no single point is structurally or functionally distinguished from all others. But it does not follow that mental functionsare localized in different parts of the brain according to the popular conception of judgment, memory, will, and so on, each depending on a special part of the brain. There is no more truth in the similar assertions of phrenology. Localization of function in this sense is impossible. Judgment is not a mental function which can be separated from memory and attention. No more separable from each other are such functions as religious sentiment, filial love, self-consciousness. The sensational, ideational, and affective elements of these functions are to a considerable extent the same.
Localization of mental functions really means this:—Since there is a division of labor among the sensory and motor organs of the body, and since each of these organs is most directly connected with certain areas of the cortex and much less directly with the other areas, it is to be expected that certain states of consciousness will occur only when certain areas of the cortex are functioning. It is but natural that the province of the cortex most directly connected with the eyes serves vision, including both visual perception and visual imagination; that the province of the cortex most directly connected with the ears serves audition. Who would expect anything else? In the same sense, the sensations of touch, of taste, and so on, are localized in the brain. The same rule holds good for movements. When our limbs move in consequence of some thought concerning them, the areas of the cortex which are most closely connected with them must function, while other areas may remain inactive. Activity of our vocal organs, in the service of our mind, can occur only by the influence of that province of the cortex which is most directly connected with the muscles of the vocal organs. But how varied are the thoughts which may bring about action of the vocal organs! On the other hand,how diversified may be the movements by which a mother may react upon the crying of her child! In either case it may be right to say that our mind is localized in the brain as a whole—not, of course, equally in every infinitesimal particle, but distributed through the brain in a manner comparable to the distribution of the roots and branches of a tree.
QUESTIONS27. To what kind of things are the neurons comparable?28. How many neurons does the nervous system contain?29. What kinds of branches does a neuron possess?30. What are white matter and gray matter?31. How does the velocity of a nervous process compare with other velocities in nature?32. What is the general function of the nervous system?33. Can you draw a diagram illustrating the architecture of a simple and of a more complex nervous system?34. How can simpler nervous functions enter into a combination without completely losing their individuality?35. What is meant by subcortical?36. What is meant by afferent and efferent neurons?37. How large is the surface of the brain?38. What is meant by sensory and motor areas of the cortex?39. Where is the seat of the soul?
QUESTIONS
27. To what kind of things are the neurons comparable?
28. How many neurons does the nervous system contain?
29. What kinds of branches does a neuron possess?
30. What are white matter and gray matter?
31. How does the velocity of a nervous process compare with other velocities in nature?
32. What is the general function of the nervous system?
33. Can you draw a diagram illustrating the architecture of a simple and of a more complex nervous system?
34. How can simpler nervous functions enter into a combination without completely losing their individuality?
35. What is meant by subcortical?
36. What is meant by afferent and efferent neurons?
37. How large is the surface of the brain?
38. What is meant by sensory and motor areas of the cortex?
39. Where is the seat of the soul?
How the functional relation between the mind and the nervous system should be explained, is a question discussed for centuries and variously answered. But all the answers are essentially either the one or the other of these two: (1) Either the brain is a tool of the mind, or (2) it is an objectified conception of the mind itself.
Popular thought, supported by desires common to all human beings, readily accepts the view that mind is essentially different from matter, that its laws are in every respect different from the laws of material nature, and that the brain, being a part of the material nature, is simply the special tool used by the mind in its intercourse with nature. Consider what a contrast seems to exist between logical certainty and the mere probability derived from more or less deceptive sense impressions, between voluntary attention and sensual desire, between religious inspiration and ordinary perception, artistic creation and everyday work. Nevertheless, these highest as well as the lowest activities of the mind need a tool with which they can get into communication with the world; and this tool, says popular thought, is the brain. By means of this tool the mind can take possession of the world and shape it at will. This explanation of the functional relation between the mind and the nervous system agrees well with the facts above discussed concerning brain weight and intelligence, and nervous pathology and mental abnormality. That the magnitude, the architecture, the normal condition of a tool have an influence on the task performed, is plain enough. Many a piece of music can be played on a large organ having a great variety of stops, whereas its performance on a small instrument would be impossible. Raffael might have deserved the name of a great painter if born without arms, but the world would never have known it.
The facts of localization of function, however, do not agree so well with this tool conception of the brain, which always leads us back again to the theory that the mind takes hold of its tool at a single point. If the mind cansuffer or producethischange only here,thatchange only there, it is difficult to see why we should regard it as an altogether separate entity. Some have pointed out, as an analogy, that truth too is everywhere, and because of its absolute unity, everywhere in its totality, without being bound to space and time. I must doubt, however, if truth is present where such analogies are worked out, for nothing can be less clear than the assertion that truth has unity. Mind is not everywhere in its totality, neither in the brain nor in the whole world. It is partly here, partly there; as seeing mind it is in the occipital convolutions of the brain, as hearing mind in the temporal convolutions. Thus we are forced, if we regard the brain as the mind’s tool, to regard the mind as an entity possessing spatial form. If we reject this conclusion, we must also reject the premise that the brain is the mind’s tool.
There are two other difficulties of very considerable importance. One of them is compliance with the principle of the conservation of energy. If mind is an entity independent of the brain, if the brain is a tool which mind can use arbitrarily, without having to obey the laws of the material world, there would be a serious break in the continuity of natural law, and the principle of the conservation of energy would suffer an exception.
Until recently it was, not probable, but at least possible, that this principle of the conservation of energy was not strictly correct when applied to conscious beings, especially to man. But in recent years direct experiment has proved that it applies to the dog, and even to man. In an animal performing no gross muscular work the energy supplied by the food is completely transformed into heat, which is absorbed by the animal’s surroundings. Rubner has found as the result of very exact measurementsthat the heat produced by an animal during several weeks is within one half of one per cent (that is, within the probable error) equal to the quantity of chemical energy received from the food. One might think that it would be rash to apply conclusions reached by experimenting on a dog to man, whose mental life stands on a much higher level. But even this objection has been removed by Atwater. He performed similar experiments on five educated persons, varying the conditions of mental and muscular activity or relative rest. The result is the same. Taking the total result, there is absolute equality between the energy supplied and the energy given out; in the human organism, mind has thus been proved to be subject to the laws of the natural world.
The second difficulty spoken of consists in the fact that, accepting the view which regards the brain as the mind’s tool, we cannot well avoid regarding the mind as a kind of ghost or demon, similar to the demons with which the imagination of primitive peoples populates the universe—gaseous and usually invisible men, women, giants, or dwarfs. Mankind has always felt strongly inclined to believe in the existence of such demons, and is still fond of making them the subjects of fairy tales and similar stories. But the more mature experience of the last centuries of human history has eliminated them from our theories of the actual world and assigned them their proper places in tales and mythology. Winter and summer, rain and sunshine, even the organic processes in the heart or the spinal cord are understood only by excluding from the explanation the assumption of such demons. The same is by analogy true for the processes in the brain, for the brain is not likely to be an exception to the rule. It is more difficult, of course, to determine directly whether such a demon exerts his influencein the inaccessible cavity of the skull than it is on the street or even in a haunted house. But no assertion is entitled to be regarded as true merely because we cannot go to the place in question and observe that it is false. Why not assert that heaven is located on the back side of the moon and hell in the center of the sun, merely because no one can see with his own eyes that they are not there? We must make only those assumptions which, considered from all points of view, have a high degree of probability, not those which flatter our vanity or appeal to us as the fashionable belief of the time. Now, it does not seem probable that our brain is the residence of a separable demon, no matter whether we attribute to him the power of changing at will the total amount of energy contained in our body, or conceive his activity, as some psychologists do, as a new form of energy added to the mechanical, thermal, electric, chemical, and so on,—requiring only an additional transformation of energy and not breaking down the principle of its conservation.
If we cannot regard the brain and the mind as two independent entities, scarcely any other conception of them is possible except as a single entity of which we may obtain knowledge in two ways, an objective and a subjective way.Mindknows itself directly, without mediation of any kind, as a complex of sense impressions, thoughts, feelings, wishes, ideals, and endeavors, non-spatial, incessantly changing, yet to some extent also permanent. Butmindmay also be known by other minds through all kinds of mediations, visual, tactual, and other sense organs, microscopes and other instruments. When thus known by other minds, mind appears as something spatial, soft, made up ofconvolutions, wonderfully built out of millions of elements, that is, as brain, as nervous system. By mind and brain we mean the same entity, viewed now in the aspect in which mind knows itself, now in the aspect in which it is known by other minds.
Suppose a person is asked a question and after some hesitation replies. In so far as this act is seen, heard, and otherwise perceived (or imagined as seen, heard, or otherwise perceived), it is a chain of physical, chemical, neurological, etc., processes, of material processes as we may say. But that part of the chain of material processes which occurs in the nervous system may not only be known by others, but may know itself directly, as a transformation of perceptual consciousness into thought, feeling, willing. The links of these two chains of material processes in the brain and of mental states should not be conceived as intermixed and thus forming one new chain, but rather as running parallel—still better as being link for link identical. The illusion that one of these chains brings forth the other is caused by the fortuitous circumstance that they do not both become conscious at once. He who thinks and feels cannot at the same time experience through his sense organs the nervous processes as which these thoughts and feelings are objectively perceptible. He who observes nervous processes cannot at the same time have the thoughts and feelings as which these processes know themselves. Those objective processes, however, which go on outside of the nervous system, in particular those outside of the experiencing organism, in the external world, precede or follow mental states as causes generally precede their effects and effects follow their causes. There is no objection to speaking of a causal relation between material processes of this kind and mental states.
Whatever explanation of the functional relation between brain and mind a person may accept, he need not constantly be on his guard lest he be inconsistent. We speak of the rising and setting sun without meaning that the earth is the center of the universe and that the sun moves around it. So we may also continue to speak quite generally of the material world as influencing our mind, and of the mind as bringing about changes in the material world.
Our view of the relation between body and mind leads to the further conclusion that, as our body may be distinguished from its parts without having existence separate from its parts, so our mind may be distinguished from the several states of consciousness without having existence separate from them. Mind is the concept of the totality of mental functions. As self-preservation is the chief end of all bodily function, so self-preservation is the chief end of mental life.
QUESTIONS40. Do the facts of comparative anatomy and of localized function agree with the view that the brain is the mind’s tool?41. Is mind subject to the law of the conservation of energy?42. Is mind a demon interfering with the laws of nature?43. What is the cause of the illusion that nervous processes bring forth mental states, or that mental states bring forth nervous processes?44. Why is it correct to regard certain events going on outside of the organism—and even in the organism, but outside of the nervous system—as effects or as causes of certain mental states?45. Is there any objection to distinguishing our mind from the several mental states?
QUESTIONS
40. Do the facts of comparative anatomy and of localized function agree with the view that the brain is the mind’s tool?
41. Is mind subject to the law of the conservation of energy?
42. Is mind a demon interfering with the laws of nature?
43. What is the cause of the illusion that nervous processes bring forth mental states, or that mental states bring forth nervous processes?
44. Why is it correct to regard certain events going on outside of the organism—and even in the organism, but outside of the nervous system—as effects or as causes of certain mental states?
45. Is there any objection to distinguishing our mind from the several mental states?
Weshall discuss first the simplest facts of mental life, later their complications. It has often been objected that such a treatment is not in harmony with the fact that we are more familiar with the complications than with the simpler facts. But we are also more familiar with our body than we are with muscle cells, nerve cells, and blood corpuscles, and yet we do not object to beginning the study of biology by a study of the structural elements and their chief properties. No one understands this to mean that the cells of various kinds existed first separately and were then combined into the body which consists of them. No one should believe that the simple mental states existed separately and were then combined into those complications with which we have become familiar in everyday life. Simple mental states are abstractions. But we cannot hope to understand the complexity of mental life without using abstractions.
Through the sense organs our mind receives information about the external world. The traditional classification of the sensations divided them into five groups. But the distinctionof five senses has been found to be insufficient. At least twice as many must be distinguished.
When psychologists tried to explain all human knowledge in terms of experience, they met with some difficulty in the description of our experience of solid bodies. Tactual sensation was found to be insufficient for this explanation, since it informs us only of the side-by-side position of things, that is, of only two dimensions. It was soon recognized that the movements of our limbs were important factors in this experience, and the question was asked: How do we perceive the spatial relations of our limbs and the resistances offered to changes in these spatial relations, that is, to movements? The first answer to this question was, that the muscles, being obviously a kind of sense organ which gives us the familiar sensations of fatigue and muscular pain, are also capable of sending in definite groups of afferent nervous processes according to their conditions of contraction and tension. This answer was quite true, as far as it went; and about 1870 the sensory neurons of muscles were actually discovered. The tendons connecting the muscles with the bones were also found to contain sensory neurons.
But this cannot be all, for we are able to judge the position of our limbs even when the muscles are completely relaxed and a limb is moved by another person. It is further a fact that a weight and the distance through which it is moved can be estimated with fair accuracy, whether the arm is sharply bent or straightened out, although the contraction and tension of the muscles is very different in these two cases. It is now known with some certainty how these estimations are made possible. The surfaces of the joints are furnished with nerves. Make a slow movement of the hand or a finger and attend to thesensation resulting from it. There is little doubt that the sensation is localized in the joint. This view is supported by the fact that electrical stimulation of a joint considerably decreases the accuracy of the estimation of weight and movement.
The three classes of sensations—muscular, tendinous, and articular—are customarily grouped together under one heading askinestheticsensations, meaning literally sensations of movement. But, as we have noted, these sensations occur as the result not only of movements of our limbs, but also of pressure or pull when the limb is at rest. They always occur together with tactual sensations, but must nevertheless be strictly distinguished from them.
Soon after this distinction had been recognized, the tactual, or rather cutaneous, sense was found to consist of several senses. The impressions of touch, that is, of pressure on the skin, of temperature, and of pain had always been distinguished; but it had not been known that the areas of greatest sensitivity for touch are not identical with those for temperature, and that the sensitivity for pain may be greatly diminished without a corresponding change in the sensitivity for touch. It was only about 1880 that these observations were explained, when an anatomical separation of the neurons serving these different sensations was demonstrated. If we test the sensitivity of the skin by carefully stimulating single points, it is found that not every point of the skin is sensitive, but that the sensitive points are isolated by larger or smaller insensitive areas. It is further found that the points sensitive to warmth are different from those sensitive to cold or to pressure or to pain. This can easily be demonstrated for the cold points by touching the skin in a number of successive points with a steel pen or a lead pencil. Generally only the touch isperceived, but now and then an intense sensation of cold is felt on definite points, always recurring when these points are touched. It is somewhat more difficult to demonstrate the points sensitive to warmth. The sensation is in this case much less noticeable. The points sensitive to touch are on hairy parts of the skin always close to a hair; on other parts, for instance the palm of the hand and particularly the finger tips, they are located so close together that their separateness can be proved only by the use of very delicate instruments. The same is to be said of the pain points of the skin. We cannot, therefore, regard the skin as one organ of sense, but must regard it as containing four classes of organs serving the senses of warmth, cold, pressure, and pain.
We must be sure, of course, to distinguish between pain, as a sensation, and the feeling of unpleasantness which almost without exception accompanies pain. We must further distinguish the sensation of pain from intense cold, intense heat, strong pressure, dazzling light, all of which may produce pain as a secondary effect. But the sensation of pain is quite dissimilar from the sensations of cold, heat, pressure, and light, to which it is added in consequence of physiological conditions. The independence of the sensation of pain can easily be demonstrated by touching the cornea of the eye with a hair. Pain is then perceived without any touch or temperature sensation. The pricking sensation in our nose resulting from the breathing of chlorine or ammonia may also be mentioned as an illustration of the same point. Let us further understand that pain is not only a cutaneous sensation, but also a sensation localized in internal organs; for instance, headache, toothache, colic.
The most interesting discovery of a new sense organconcerns the labyrinth of the ear. It was made quite unexpectedly. The labyrinth consists of the inner ear proper, or the cochlea, the system of three semicircular canals, and between these two organs a pair of small sacs, each containing a little stone or otolith, built of microscopic lime crystals. All these organs, being all of the nature of cavities filled with fluid and communicating, were originally regarded as serving the sense of hearing, although no one was able to say how. It was observed, however, that stimulation or lesion of the semicircular canals and of the sacs did not affect hearing, but resulted in disturbances of the coördination of the muscular activities in locomotion and normal position. For more than fifty years these observations remained unexplained; and even then their explanation was but slowly accepted.
It is now recognized that the semicircular canals and the sacs are not organs of hearing, but organs informing the organism about the movements or position of the head, and indirectly of the body as a whole. The sensations coming from these organs are usually so closely bound up with kinesthetic and tactual sensations that we have not learned to become conscious of them as a separate kind. Nevertheless we may perceive them separately under favorable circumstances. If we close our eyes, turn quickly a few times on our heel, and suddenly stop, we are vividly conscious of being turned in the opposite direction. This is a perception mediated by the semicircular canals. The fluid ring in the horizontal canal gradually assumes the motion of the body, in consequence of its friction against the walls; and when the body suddenly stops moving, the fluid ring continues to move and to stimulate the sensory neurons for some time. If the body moves in a larger circle, for example on a merry-go-round or on a street car passingaround a curve, the mind perceives an inclination of the body towards the convex side of the curve. If we go up in an elevator, we have the impression, just after the elevator has stopped, of moving a short distance down. These are sensations of the otolith organs.
The otoliths are slightly movable, one in the horizontal, the other in the vertical direction. If the body moves through a curve, the otolith which by centrifugal force is driven outwards stimulates the sensory neurons in the same manner in which it stimulates them when the body is inclined. The perception of the body’s position is therefore the same. If the body is quickly moved up or down, the vertical otolith at first lags behind, and at the stop, through its inertia, continues to move a little in the same direction. The result is a brief perception of the body moving in the opposite direction.
Artificial stimulation or lesion of the semicircular canals or otolith organs in animals tends to produce certain unexpected reflex movements of the body which the animal tries to counteract voluntarily, so that all kinds of unusual movements are observed. If these organs are destroyed, one source of information about the position and the movements of the body is lost. This loss is not very serious in man, in whom it occurs as a result of diseases of the ear; man can obtain his orientation from visual, kinesthetic, and pressure sensations in spite of this loss. It is far more serious in aquatic and flying animals. Pressure differences are of no account when the body has nothing but water or air on all sides. In a greater depth of water vision is practically impossible. Under these circumstances the semicircular canals and the otolith organs are highly important for an animal’s life. Unfortunately no definite names have thus far been adopted for these senses. Theyare frequently called the static sense or the sense of equilibrium. But these names are of doubtful value, since other senses too may inform us about our equilibrium.
The enumeration of our senses is not yet completed. What is hunger? What is thirst? What is nausea? These mental states are certainly similar, in some respects, to tones and odors. They are sensations. There is the difference, however, that we do not project them into external space, but think of them as characteristics of our own body’s condition. How is consciousness of these sensations brought about? No doubt, in a manner similar to that of the mediation of such sensations as odors and tones: through the stimulation of sensory neurons and the propagation of nervous processes toward the motor points of the body. The place of stimulation must be somewhere in our organs of nutrition, and thus these organs must be regarded also as a kind of sense organ. That the sensory function can be attributed to an organ in addition to another function has been proved by the example of the skin, muscles, and joints. The same may be said of other organs, for instance the lungs giving us the sensation of suffocation.
We possess, therefore, a large number of organs whose primary function is of an active kind, but which also give information as to the condition of those active functions. The sensations resulting from them are as independent of each other as tones are of color or taste. But they do not permit of as many subdivisions as the sensations of the so-called higher senses. For the emotional part of our mental life they are of the greatest significance. Since we do not project them into the external world, but think of them as significant of the functions of our internal organs, they are rightly called by the common name oforganic sensations.
Besides the cutaneous sensations four classes were known to the older psychology: sensations of color, sound, odor, and taste. The relation of these sensations to the corresponding stimuli comprises a vast number of problems and theories, but we shall here state merely that which is of more general interest.
The taste—in the ordinary sense—of a substance is by no means made up exclusively of taste sensations in the special sense of this term. It is usually a complex of different sensations which almost invariably occur together. Only gradually do we learn to analyze this complex into its elements. Touch sensations of the tongue and palate often enter into the combination, for instance in a burning or astringent taste. Sensations of smell are of particular importance in this connection. The different kinds of meat, of wine, of bread, and of many other foods and beverages are distinguished almost exclusively by the smell. Aside from these accompanying sensations, there are only four tastes proper: sweet, sour, salt, bitter, in all their possible mixtures and relative degrees of intensity. In a manner comparable to the distribution of cutaneous sensations, the taste sensations have their end organs at definite points in the papillæ of the tongue and soft palate. The so-called taste buds contained in the walls of the papillæ seem to be sensitive according to the principle of the division of labor, some serving chiefly this, others chiefly that taste. It is possible that all the taste buds of the same papilla mediate the same taste sensation, so that each papilla might be said to be in the service of a particular taste.
The number of distinguishable odors is very large. Gaseous, fluid, and solid substances, minerals, plants, andanimals have usually their characteristic, although often very faint, odors. As new substances are discovered or new mixtures of substances invented, the number of odors is increased. Unfortunately it has thus far been impossible to arrange this multitude of odors in a system according to a simple plan. Various groups of related odors have been formed by investigators (for example, the odor of flowers, fruit, musk, onion, decaying matter). But it is difficult to include all possible odors in such groups; and the relation between these groups is still unknown. One reason for this difficulty in understanding theoretically the sense of smell is the obvious fact that this sense has degenerated in man. The organ of smell, a spot in the upper part of each nasal cavity, is of small extent in man compared with that of animals. Even more superior are the animals to man with respect to the development of the olfactory nerve center. The degeneration is the result of a lack of use. Man, walking upright, has but rarely an opportunity of approaching objects with his nostrils closely enough to be able to smell them. The animal, searching for food on the ground, smells unceasingly.
The opposite is true for color sensations. They, too, are numerous, perhaps a million. But it is easy to group them into a system which permits us to understand their interrelations. The relations between the various colors are so simple that they can be symbolically represented by a geometrical figure, a double pyramid with a four-cornered base, like the one in figure 14. The vertical axis represents the visual sensations which are colorless, arrayed so that the brightest white is at one end, the darkest black at the other, the various grays between. The base of the pyramids, which is not perpendicular to the axis, but slanting, represents the series of colors of