Fig. 16.--Side view of the left hemisphere, showing the location of the "speech centers." The region marked "Motor" is the motor speech center, that marked "Auditory" the auditory speech center, and that marked "Visual" the visual speech center. (Figure text: central fissure, motor area, auditory area, visual area, fissure of Sylvius, brain stem, cerebellum)
In pure cases ofmotor aphasia, the subject knows the words he wishes to say, but cannot get them out. The brain injury here lies in the frontal lobe in the left hemisphere, in right-handed people, just forward of the motor area for the mouth, tongue and larynx. This "motor speech center" is the best-known instance of a super-motor center. It coördinates the elementary speech movements into the combinations called words; and perhaps there is no other motor performance so highly skilled as this of speaking. It is acquired so early in life, and practised so constantly, that{59}we take it quite as a matter of course, and think of a word as a simple and single movement, while in fact even a short word, as spoken, is a complex movement requiring great motor skill.
There is some evidence that the motor speech center extends well forward into the frontal lobe, and that the front part of it is related to the part further back as this is to the motor area back of it. That is to say, the back of the speech center combines the motor units of the motor area into the skilled movements of speaking a word, while the more forward part of the speech center combines the word movements into the still more complex movement of speaking a sentence. It is even possible that the very front part of the speech center has to do with those still higher combinations of speech movements that give fluency and real excellence of speaking.
Besides the motor aphasia, just mentioned, there is another type, calledsensory aphasia, or, more precisely, auditory aphasia. In pure auditory aphasia there is no inability to pronounce words or even to speak fluently, but there is, first, an inability to "hear words", sometimes called word deafness, and there is often also an inability to find the right words to speak, so that the individual so afflicted, while speaking fluently enough and having sense in mind, misuses his words and utters a perfect jargon. One old gentleman mystified his friends one morning by declaring that he must go and "have his umbrella washed", till it was finally discovered that what he wanted was to have his hair cut.
The cortical area affected in this form of aphasia is located a little further back on the surface of the brain than{60}the motor speech center, being close to the auditory area proper. The latter is a small cortical region in the temporal lobe, connected (through lower centers) with the ear, and is the only part of the cortex to receive nerve currents from the organ of hearing. The auditory area is, indeed, the organ of hearing, or an organ of hearing, for without it the individual is deaf. He may make a few reflex responses to loud noises, but, consciously, he does not hear at all; he has no auditory sensations.
In the immediate neighborhood of the auditory area proper (or of the "auditory-sensory area", as it may well be called), are portions of the cortex intimately connected by axons with it, and concerned in what may be called auditory perceptions, i.e., with recognizing and understanding sounds. Probably different portions of the cortex near the auditory-sensory center have to do with different sorts of auditory perception. At least, we sometimes find individuals who, as a result of injury or disease affecting this general region, are unable any longer to follow and appreciate music. They cannot "catch the tune" any longer, though they may have been fine musicians before this portion of their cortex was destroyed. In other cases, we find, instead of this music deafness, the word deafness mentioned just above.
The jargon talk that so often accompanies word deafness reminds us of the fact that speech is first of all auditory to the child. He understands what is said to him before he talks himself, and his vocabulary for purposes of understanding always remains ahead of his speaking vocabulary. It appears that this precedence of auditory speech over motor remains the fact throughout life, in most persons, and that the auditory speech center is the most fundamental of all the speech centers, of which there is one more not yet mentioned, used in reading.
{61}
Fig. 17.--(From Cajal.) Magnified sections through the cortex, to show the complexity of its inner structure. One view shows nerve cells and their dendrites, with only a few axons, while the other shows axons, outgoing and incoming, and some of their fine branches. Imagine one view superimposed upon the other, and you get some idea of the intricate interweaving of axons and dendrites that occurs in the cortex.
{62}
There is a visual-sensory area in the occipital lobe, at the back of the brain, that is connected with the eye in the same way as the auditory center is connected with the ear. Without it, the individual still shows the pupillary reflex to light, but has no sensations of sight. He is blind.
Fig. 18.--Vertical cross-section through the brain, showing the cortex on the outside, the thalamus and other interior masses of gray matter, some of the paths to and from the cortex, and the callosum or bridge of axons connecting the two cerebral hemispheres. The "Motor path" is the pyramidal tract, only the beginning of which is shown here, its further course being indicated inFig. 14.(Figure text: tactile path, motor path, auditory path, callosum, thalamus, olfactory area)
This visual-sensory area occupies only a small portion of the occipital lobe, and yet practically the whole lobe is concerned with vision. Some portions of the lobe are concerned in perceiving words in reading, and without them the individual is "word blind". Other portions are concerned in perceiving (recognizing, understanding) seen objects, and without them the individual is "object blind". Other{63}portions are concerned in perceiving color relations, and still other portions in perceiving spatial relations through the sense of sight and so knowing where seen objects are and being able to guide one's movements by sight.
There is an olfactory area in a rather secluded part of the cortex, and this is related to the sense of smell in the same general way. Probably there is a similar taste center, but it has not been definitely located. Then there is a large and important area called the "somesthetic", connected with the body senses generally, i.e., chiefly with the skin and muscle senses. This area is located in a narrow strip just back of the central fissure, extending parallel to the motor area which lies just in front of the fissure, and corresponding part for part with it, so that the sensory area for the legs lies just behind the motor area for the legs, and so on. Destruction of any part of this somesthetic area brings loss of the sensations from the corresponding part of the body.
Just behind this direct sensory center for the body, in the parietal lobe, are portions of the cortex concerned in perceiving facts by aid of the body senses. Perception of size and shape by the sense of touch, perception of weight by the muscle sense, perception of degrees of warmth and cold by the temperature sense, are dependent on the parietal lobe and disappear when the cortex of this region is destroyed. It appears that there is a sort of hierarchy of centers here, as in the motor region and probably also in the visual and auditory regions. Skill in handling objects is partly dependent on the "feel" of the objects and so is impaired by injuries to the parietal lobe, as well as by injury to the frontal lobe; and knowing how to manage a fairly complex situation, as in lighting a fire when you have the various{64}materials assembled before you, seems also to depend largely on this part of the cortex.
Fig. 19.--Sensory path from the skin of any portion of the trunk or limbs. The path consists of three neurones, the cell body of the first lying just outside the spinal cord, that of the second lying in the cord, and that of the third lying in the thalamus. The last part of this path is the "Tactile path," shown inFig. 18.(Figure text: cortex, thalamus, cord, skin)
As already indicated, no portion of the cortex, not even the sensory areas, is directly connected with any sense organ. The sensory axons from the skin, for example, terminate in the spinal cord, in what may be called the lowest sensory centers. Here are nerve cells whose axons pass up through the cord and brain stem to the thalamus or interbrain, where they terminate in a second sensory center. And cells here send their axons up to the somesthetic area of the cortex.
{65}
The thalamus is remarkable as an intermediate center for all the senses, except smell; but exactly what is accomplished by this big intermediate sensory center remains rather a mystery, though it certainly appears that the thalamus has something to do with feeling and emotion.
Regarding the cerebellum, there is much knowledge at hand, but it is difficult to give the gist of it in a few words. On the one hand, the cerebellum receives a vast number of axons from the lower sensory centers; while, on the other hand, it certainly has nothing to do with conscious sensation or perception. Its use seems to be motor. It has much to do with maintaining the equilibrium of the body, and probably also with maintaining the steadiness and general efficiency of muscular contraction. Though it has no known sensory or intellectual functions, it is very closely connected with the cerebrum, receiving a tremendous bundle of axons from different parts of the cerebrum, by way of the brain stem. Possibly these are related to motor activity. The phrenologists taught that the cerebellum was the center for the sexual instinct, but there is no evidence in favor of this guess.
Let a noise strike the ear and start nerve currents in along the auditory nerve, passing through the lowest and intermediate centers and reaching the auditory-sensory area of the cortex. When this last is aroused to activity, we have a sensation of sound, which is the first conscious reaction to the external stimulus. Axons running from the auditory-sensory to the near-by cortex give a perception of some fact indicated by the external stimulus, and this perception is a{66}second and higher conscious reaction, which, to be sure, ordinarily occurs so quickly after the first that introspection cannot distinguish one as first and the other as second; but the facts of brain injury, already mentioned, enable us to draw the distinction. The perceived fact may call up a mental image, or a recognition of some further fact less directly signified by the noise; these would be reactions of still higher order. Much of the cortex is apparently not very directly connected with either the sensory or the motor areas, and probably is concerned somehow in the recognition of facts that are only very indirectly indicated by any single sensory stimulus, or with the planning of actions that only indirectly issue in muscular movement.
On the sensory and intellectual side, the higher reactions follow the lower: sensation arouses perception and perception thought. On the motor side, the lower reactions are aroused by the higher. Thus the speech center arouses the motor centers for the speech organs, combining the action of these into the speaking of a word; and in a similar way, it seems, the intention to speak a sentence expressing a certain meaning acts as a stimulus to call up in order the separate words that make the sentence. A general plan of action precedes and arouses the particular acts and muscular movements that execute the plan.
{67}
1. Outline of the chapter. Fill in sub-topics under each of the following heads:
A. Mental processes of all kinds are reactions.B. The stimulus that directly arouses a mental process is often "central".C. Brain activities of all sorts influence the muscles by way of the motor area and the lower motor centers.D. Brain action in skilled movement.E. Brain action in speech.F. Brain action in sensation.G. Brain action in recognizing seen or heard objects.H. Relations of reactions of different levels.
2. Define and illustrate these classes of stimuli:
A. Peripheral:
(1) External.(2) Internal.
B. Central.
3. Show by a diagram how one cortical center arouses another. Compare the diagram in Fig. 9, p. 37.4. Facilitation of the patellar reflex or "knee jerk". Let your subject sit with one leg hanging freely from the knee down. With the edge of your hand strike the patellar tendon just below the knee cap. (a) Compare the reflex movement so obtained with a voluntary imitation by the subject. Which is the quicker and briefer? (b) Apply a fairly strong auditory stimulus (a sudden noise) a fraction of a second before the tap on the tendon, and see whether the reflex response is reinforced, (c) Ask the subject to clench his fists or grit his teeth, and tap the tendon as he does so. Reinforcement? (d) Where is the reflex center for the patellar reflex, and whence comes the reinforcing influence?5. Construct a diagram showing the different centers and connections involved in making the skilled movement of writing; and consider what loss of function would result from destruction of each of the centers.
Herrick'sIntroduction to Neurology, 1918, Chapter XX, on the "Functions of the Cerebrum".
Stile'sNervous System and Its Conservation, Chapters X, XI and XII.
{68}
One advantage of basing our psychology onreactionsis that it keeps us "close to the ground", and prevents our discussions from sailing off into the clouds of picturesque but fanciful interpretation. Psychology is very apt to degenerate into a game of blowing bubbles, unless we pin ourselves down to hard-headed ways of thinking. The notion of a reaction is of great value here, just because it is so hard-headed and concrete. Whenever we have any human action before us for explanation, we have to ask what the stimulus is that arouses the individual to activity, and how he responds. Stimulus-response psychology is solid, and practical as well; for if it can establish the laws of reaction, so as to predict what response will be made to a given stimulus, and what stimulus can be depended on to arouse a desired response, it furnishes the "knowledge that is power". Perhaps no more suitable motto could be inscribed over the door of a psychological laboratory than these two words, "Stimulus-Response."
Such a motto would not frighten away the modern introspectionists, for they, no less than the behaviorists, could find a congenial home in a stimulus-response laboratory. They would begin by studying sensations, and, advancing to more complex responses, would observe the conscious processes entering into the response.
{69}
But, however useful the reaction may be as affording a sound basis for psychological study, we must not allow it to blind our eyes to any of the real facts of mental life; and, at first thought, it seems as ifmotives, interestsandpurposesdid not fit into the stimulus-response program. Many hard-headed psychologists have fought shy of such matters, and some have flatly denied them any place in scientific psychology. But let us see.
S ---> RFig. 20.--The symbol of stimulus-response psychology.Smeans the stimulus, andRthe response. The line between is the connection from stimulus to response.
Suppose we are looking out on a city street during the noon hour. We see numbers of people who--lunch over, nothing to do till one o'clock!--are standing or walking about, looking at anything that chances to catch their eye, waving their hands to friends across the street, whistling to a stray dog that comes past, or congregating about an automobile that has broken down in the crowded thoroughfare. These people are responding to stimuli, obviously enough, and there is no difficulty in fitting their behavior into the stimulus-response scheme.
But here comes some one who pays little attention to the sights and sounds of the street, simply keeping his eyes open enough to avoid colliding with any one else. He seems in a hurry, and we say of him, "He must have business on hand; he has to keep an appointment or catch a train". He is not simply responding to the stimuli that come to him, but has some purpose of his own that directs his movements.
Here is another who, while not in such a hurry, is not idling by any means, since he peers closely at the faces of the men, neglecting the women, and seems to be looking for some one in particular; or, perhaps, he neglects men and{70}women alike, and looks anxiously at the ground, as if he had lost something. Some inner motive shuts him off from most of the stimuli of the street, while making him extra responsive to certain sorts of stimuli.
Now it would be a great mistake to rule these purposeful individuals out of our psychology. We wish to understand busy people as well as idlers. What makes a man busy is some inner purpose or motive. He still responds to present stimuli--otherwise he would be in a dream or trance and out of all touch with what was going on about him--but his actions are in part controlled by an inner motive.
To complete the foundations of our psychology, then, we need to fit purpose into the general plan of stimulus and response. At first thought, purpose seems a misfit here, since--
First, a purpose is an inner force, whereas what arouses a response should be a stimulus, and typically an external stimulus. We do not wish to drop back into the old "self-activity" psychology, which thought of the individual as originating his acts from within himself. But if we could show that a purpose is itself an inner response to some external stimulus, and acts in its turn as a "central stimulus" to further reactions, this difficulty would disappear.
Second, while a typical reaction, like the reflex or the simple reaction of the experiment, is prompt and over with at once, a purpose persists. It keeps the busy man, in our illustration, hurrying all the way down the street and around the corner and how much farther we cannot say. It is very different from a momentary response, or from a stimulus that arouses a momentary response and nothing more.
Third, what persists, in purposive behavior, is the tendency{71}towards some end or goal. The purposeful person wants something he has not yet got, and is striving towards some future result. Whereas a stimulus pushes him from behind, a goal beckons to him from ahead. This element of action directed towards some end is absent from the simple response to a stimulus.
In short, we have to find room in our stimulus-response psychology for action persistently steered in a certain direction by some cause acting from within the individual. We must find room forinternalstates thatlastfor a time anddirectaction. In addition, we sometimes, though not always, need to find room for conscious foreknowledge of the goal towards which the action is directed.
Fig. 21.--The stimulus-response scheme complicated to allow for the existence of T, an inner motive or tendency, which, aroused by an external stimulus, itself arouses a motor response. If the reaction-tendency were linked so firmly to a single response as to arouse that response with infallible certainty and promptness, then it would be superfluous for psychology to speak of a tendency at all. But often quite a series of responses, R1, R2, etc., follows upon a single stimulus, all tending towards the same end-result, such as escape; and then the notion of a "tendency" is by no means superfluous.
"Purpose" is not the best general term to cover all the internal factors that direct activity, since this word rather implies foresight of the goal, which demands the intellectual ability to imagine a result not present to the senses. This highest level of inner control over one's behavior had best be left for consideration in later chapters on imagination and will. There are two levels below this. In the middle level, the individual has an inner steer towards a certain result, though without conscious foresight of that result. At the lowest level, we can scarcely speak of the individual as being directed towards any precise goal, but still his{72}internal state is such as to predispose him for certain reactions and against other reactions.
The lowest level, that of organic states, is typified by fatigue. The middle level, that of internal steer, is typified by the hunting dog, striving towards his prey, though not, as far as we know, having any clear idea of the result at which his actions are aimed. The highest level, that of conscious purpose, is represented by any one who knows exactly what he wants and means to get.
No single word in the language stands out clearly as the proper term to cover all three levels. "Motives" would serve, if we agree at the outset that a motive is not always clearly conscious or definite, but may be any inner state or force that drives the individual in a given direction. "Wants" or "needs" might be substituted for "motives", and would apply better than "motives" to the lowest of our three levels. "Tendencies", or "tendencies to reaction", carries about the right meaning, namely that the individual, because of his internal state, tends towards a certain action. "Determining tendencies" (perhaps better, "directive tendencies") is a term that has been much used in psychology, with the meaning that the inner tendency determines or directs behavior. Much used also are "adjustment" and "mental set", the idea here being to liken the individual to an adjustable machine which can be set for one or another sort of work. Often "preparation" or "readiness for action" is the best expression.
Beginning at the lowest of our three levels, let us observe not even the simplest animal, but a single muscle. If we give a muscle electric shocks as stimuli, it responds to each shock by contracting. To a weak stimulus, the response is weak;{73}to a strong stimulus, strong. But now let us apply a long series of equal shocks of moderate intensity, one shock every two seconds. Then we shall get from the muscle what is called a "fatigue curve", the response growing weaker and weaker, in spite of the continued equality of the stimuli. How is such a thing possible? Evidently because the inner condition of the muscle has been altered by its long-continued activity. The muscle has become fatigued, and physiologists, examining into the nature of this fatigue, have found the muscle to be poisoned by "fatigue substances" produced by its own activity. Muscular contraction depends on the oxidation of fuel, and produces oxidized wastes, of which carbon dioxide is the best known; and these waste products, being produced in continued strong activity faster than the blood can carry them away, accumulate in the muscle and partially poison it. The "organic state" is here definitely chemical.
Fig. 22.--Fatigue curve of a muscle. The vertical lines record a series of successive contractions of the muscle, and the height of each line indicates the force of the contraction. Read from left to right.
This simple experiment is worth thinking over. Each muscular contraction is a response to an electric stimulus, but the force of the contraction is determined in part by the internal state of the muscle. Fatigue is aninnerstate of the muscle thatpersistsfor a time (till the blood carries away the wastes), and thatpredisposesthe muscletowardsa certain kind of response, namely, weak response. Thus the three characteristics of purposive behavior that seemed so{74}difficult to fit into the scheme of stimulus and response are all here in a rudimentary form.
But notice this fact also: the inner condition ofmuscular fatigue is itself a responseto external stimuli. It is part and parcel of the total muscular response to a stimulus. The total response includes an internal change of condition, which, persisting for a time, is a factor in determining how the muscle shall respond to later stimuli. These facts afford, in a simple form, the solution of our problem.
Before leaving the muscle, let us take note of one further fact. If you examine the "fatigue curve" closely, you will see that a perfectly fresh musclegainsin strength from its first few responses. It is said to "warm up" through exercise; and the inner nature of this warming up has been found to consist in a moderate accumulation of the same products which, in greater accumulation, produce fatigue. The warmed-up condition is then another instance of an "organic state".
There will be more to say of "organic states" when we come to the emotions. For the present, do not the facts already cited compel us to enlarge somewhat the conception of a reaction as we left it in the preceding chapters? Besides the external response, there is often an internal response to a stimulus, a changed organic state that persists for a time and has an influence on behavior. The motor response to a given stimulus is determined partly by that stimulus, and partly by the organic state left behind by just preceding stimuli. You cannot predict what response will be made to a given stimulus, unless you know the organic state present when the stimulus arrives.
At the second level, the inner state that partly governs the response is more neural than chemical, and is directed{75}specifically towards a certain end-result. As good an instance as any is afforded by the "simple reaction", described in an earlier chapter. If the subject in that experiment is to raise his finger promptly from the telegraph key on hearing a given sound, he must beprepared, for there is no permanent reflex connection between this particular stimulus and this particular response. You tell your subject to be ready, whereupon he places his finger on the key, and gets all ready for this particular stimulus and response. The response is determined as much by his inner state of readiness as by the stimulus. Indeed, he sometimes gets too ready, and makes the response before he receives the stimulus.
The preparation in such a case is more specific, less a general organic state, than in the previous cases of fatigue, etc. It is confined for the most part to the nervous system and the sense organ and muscles that are to be used. In an untrained subject, it includes a conscious purpose to make the finger movement quickly when the sound is heard; but as he becomes used to the experiment he loses clear consciousness of what he is to do. He is, as a matter of fact, ready for a specific reaction, but all he is conscious of is a general readiness. He feels ready for what is coming, but does not have to keep his mind on it, since the specific neural adjustment has become automatic with continued use.
Examples of internal states of preparedness might be multiplied indefinitely, and it may be worth while to consider a few more, and try out on them the formula that has already been suggested, to the effect that preparation is an inner adjustment for a specific reaction, set up in response to some stimulus (like the "Ready!" signal), persisting for a time, and predisposing the individual to make the specified reaction whenever a suitable stimulus for it arrives. The preparation may or may not be conscious. It might be named "orientation" or "steer", with the meaning that{76}the individual is headed or directed towards a certain end-result. It is like so setting the rudder of a sailboat that, when a puff of wind arrives, the boat will respond by turning to the one side.
The runner on the mark, "set" for a quick start, is a perfect picture of preparedness. Here the onlookers can see the preparation, since the ready signal has aroused visible muscular response in the shape of a crouching position. It is not simple crouching, but "crouching to spring." But if the onlookers imagine themselves to be seeing the whole preparation--if they suppose the preparation to be simply an affair of the muscles--they overlook the established fact that the muscles are held in action by the nerve centers, and would relax instantly if the nerve centers should stop acting. The preparation is neural more than muscular. The neural apparatus is set to respond to the pistol shot by strong discharge into the leg muscles.
What the animal psychologists have called thedelayed reactionis a very instructive example of preparation. An animal is placed before a row of three food boxes, all looking just alike, two of them, however, being locked while the third is unlocked. Sometimes one is unlocked and sometimes another, and the one which at any time is unlocked is designated by an electric bulb lighted above the door. The animal is first trained to go to whichever box shows the light; he always gets food from the lighted box. When he has thoroughly learned to respond in this way, the "delayed reaction" experiment begins. Now the animal is held while the light is burning, and only released a certain time after the light is out, and the question is whether, after this delay, he will still follow the signal and go straight to the right door. It is found that he will do so, provided the delay is not too long--how long depends on the animal. With rats the delay cannot exceed 5 seconds, with cats it can reach 18{77}seconds, with dogs 1 to 3 minutes, with children (in a similar test) it increased from 20 seconds at the age of fifteen months to 50 seconds at two and a half years, and to 20 minutes or more at the age of five years.
Rats and cats, in this experiment, need to keep their heads or bodies turned towards the designated box during the interval between the signal and the release; or else lose their orientation. Some dogs, however, and children generally, can shift their position and still, through some inner orientation, react correctly when released. The point of the experiment is that the light signal puts the animal or child into a state tending towards a certain result, and that, when that result is not immediately attainable, the state persists for a time and produces results a little later.
In the delayed reaction, the inner orientation does little during the interval before the final reaction, except to maintain a readiness for making that reaction; but often "preparatory reactions" occur before the final reaction can take place. Suppose you whistle for your dog when he is some distance off and out of sight. You give one loud whistle and wait. Presently the dog swings around the corner and dashes up to you. Now, what kept the dog running towards you after your whistle had ceased and before he caught sight of you? Evidently he was directed towards the end-result of reaching you, and this directing tendency governed his movements during the process. He made many preparatory reactions on the way to his final reaction of jumping up on you; and these preparatory reactions were, of course, responses to the particular trees he had to dodge, and the ditches he had to jump; but they were at the same time governed by the inner state set up in him by your {78 } whistle. This inner state favored certain reactions and excluded others that would have occurred if the dog had not been in a hurry. He passed another dog on the way without so much as saying, "How d'ye do?" And he responded to a fence by leaping over it, instead of trotting around through the gate. That is to say, the inner state set up in him by your whistlefacilitatedreactions that were preparatory to the final reaction, andinhibitedreactions that were not in that line.
A hunting dog following the trail furnishes another good example of a directive tendency. Give a bloodhound the scent of a particular man and he will follow that scent persistently, not turning aside to respond to stimuli that would otherwise influence him, nor even to follow the scent of another man. Evidently an inner neural adjustment has been set up in him predisposing him to respond to a certain stimulus and not to others.
The homing of the carrier pigeon is a good instance of activity directed in part by an inner adjustment, since, when released at a distance from home, he is evidently "set" to get back home, and often persists and reaches home after a very long flight. Or, take the parallel case of the terns, birds which nest on a little island not far from Key West. Of ten birds taken from their nests and transported on shipboard out into the middle of the Gulf of Mexico and released 500 miles from home, eight reappeared at their nests after intervals varying from four to eight days. How they found their way over the open sea remains a mystery, but one thing is clear: they persisted in a certain line of activity until a certain end-result was reached, on which this line of activity ceased.
One characteristic of tendencies that has not previously been mentioned comes out in this example. When a tendency has been aroused, the animal (or man) is tense and{79}restless till the goal has been reached, and then quiets down. The animal may or may not be clearly conscious of the goal, but he is restless till the goal has been attained, and his restlessness then ceases. In terms of behavior, what we see is a series of actions which continues till a certain result has been reached and then gives way to rest. Introspectively, what we feel (apart from any clear mental picture of the goal) is a restlessness and tenseness during a series of acts, giving way to relief and satisfaction when a certain result has been reached.
A hungry or thirsty animal is restless; heseeksfood or drink, which means that he is making a series of preparatory reactions, which continues till food or drink has been found, and terminates in the end-reaction of eating or drinking.
The behavior of a hungry or thirsty individual is worth some further attention--for it is the business of psychology to interest itself in the most commonplace happenings, to wonder about things that usually pass for matters of course, and, if not to find "sermons in stones", to derive high instruction from very lowly forms of animal behavior. Now, what is hunger? Fundamentally an organic state; next, a sensation produced by this organic state acting on the internal sensory nerves, and through them arousing in the nerve centers an adjustment or tendency towards a certain end-reaction, namely, eating. Now, I ask you, if hunger is a stimulus to the eating movements, why does not the hungry individual eat at once? Why, at least, does he not go through the motions of eating? You say, because he has nothing to eat. But he could still make the movements; there is no physical impossibility in his making chewing and swallowing movements without the presence of food.{80}Speaking rationally, you perhaps say that he does not make these movements because he sees they would be of no use without food to chew; but this explanation would scarcely apply to the lower sorts of animal, and besides, you do not have to check your jaws by any such rational considerations. They simply do not start to chew except when food is in the mouth. Well, then, you say, chewing is a response to the presence of food in the mouth; and taking food into the mouth is a response to the stimulus of actually present food. The response does not occur unless the stimulus is present; that is simple.
Not quite so simple, either. Unless one is hungry, the presence of food does not arouse the feeding reaction; and even food actually present in the mouth will be spewed out instead of chewed and swallowed, if one is already satiated. Try to get a baby to take more from his bottle than he wants! Eating only occurs when one isbothhungry and in the presence of food. Two conditions must be met: the internal state of hunger and the external stimulus of food; then, and then only, will the eating reaction take place.
Hunger, though a tendency to eat, does not arouse the eating movements while the stimulus of present food is lacking; but, for all that, hunger does arouse immediate action. It typically arouses the preparatory reactions of seeking food. Any such reaction is at the same time a response to some actually present stimulus. Just as the dog coming at your whistle was responding every instant of his progress to some particular object--leaping fences, dodging trees--so the dog aroused to action by the pangs of hunger begins at once to respond to present objects. He does not start to eat them, because they are not the sort of stimuli that produce this response, but he responds by dodging them or finding his way by them in his quest for food. The responses that the hungry dog makes to other objects than{81}food are preparatory reactions, and these, if successful, put the dog in the presence of food. That is to say, thepreparatory reactions provide the stimulus that is necessary to arouse the end-reaction. They bring the individual to the stimulus, or the stimulus to the individual.
Fig. 23.--A stimulus arouses the tendency towards the end-reaction, R, but (as indicated by the dotted line), T is not by itself sufficient to arouse R; but T can and does arouse P, a preparatory reaction, and P (or some external result directly produced by P), coöperating with T, gives rise to R.
What we can say about the modus operandi of hunger, then, amounts to this: Hunger is an inner state and adjustment predisposing the individual to make eating movements in response to the stimulus of present food; in the absence of food, hunger predisposes to such other responses to various stimuli as will bring the food stimulus into play, and thus complete the conditions necessary for the eating reaction. In general,an aroused reaction-tendency predisposes the individual to make a certain end-reaction when the proper stimulus for that reaction is present; otherwise, it predisposes him to respond to other stimuli, which are present, by preparatory reactions that eventually bring to bear on the individual the stimulus required to arouse the end-reaction.
Let us apply our formula to one more simple case. While reading in the late afternoon, I find the daylight growing dim, rise and turn on the electric light. The stimulus that sets this series of acts going is the dim light; the first, inner response is aneedfor light. This need tends, by force of habit, to make me turn the button, but it does not make me execute this movement in the air. I only make this movement when the button is in reaching distance. My first{82}reaction, rising from my chair, is preparatory and brings the button close enough to act as a stimulus for the hand reaction. The button within reach is not by itself sufficient to arouse the turning reaction, nor is the need for light alone sufficient. The two conditions must be present together, and the preparatory reaction is such that, given the need, the other condition will be met and the reaction then aroused.
Very little need be added to our neural conception of a reaction in order to get a satisfactory conception of a tendency to reaction. Principally, we must add this fact, that a nerve center aroused to activity does not always discharge instantly and completely into the muscles, or into some other center, and come to rest itself. It does so, usually, in the case of a reflex, and in other momentary reactions; as when A makes you think of B, and B at once of C, and so on, each thought occupying you but a moment. But a tendency means the arousing of a nerve center under conditions which do not allow that center to discharge at once. The center remains in a condition of tension; energy is dammed up there, unable to find an outlet.
We have already seen what the conditions are that cause this damming up of energy. The center that is aroused tends to arouse in turn some lower motor center, but by itself does not have complete control over that lower center, since the lower center also requires a certain external stimulus in order to arouse it to the discharging point. Until the proper external stimulus arrives to complete the arousal of the lower center, the higher center cannot discharge its energy.
When there is an "organic state" present, such as hunger or thirst, this may act as a persistent stimulus to the sensory nerves and through them to the higher center in{83}question; and then we can readily understand how it is that the center remains active until the organic state is relieved. But where there is no such persistent organic stimulus, as there can scarcely be in the case of the bloodhound or of the man hurrying to a train or seeking in the crowd for a friend, there we have to suppose that a center, once aroused to activity and prevented from complete discharge, remains active by virtue of energy dammed up in itself. There is pretty good physiological evidence that this sort of thing is a fundamental fact; for there are certain rhythmical reflexes, like scratching or stepping, that, when started going by a momentary sensory stimulus, keep it up for a time after the stimulus has ceased. There seems to be no doubt that a nerve center, once aroused, may stay aroused for a time.
The "dammed-up energy" here is not to be confused with the "stored energy" spoken of under the head of reactions. We said, in that connection, that a stimulus released energy stored in the organism. That, however, waspotentialenergy, dormant within the organism till aroused; but what we have here in mind is active orkineticenergy. Stored energy is like that of coal in the bin; dammed-up energy is like that of steam in the boiler.
Dammed-up energy in the nerve centers accounts for the persistence of a tendency to reaction after the stimulus has ceased. It accounts for the "delayed reaction" and similar cases. But how shall we account for preparatory reactions? We have a nerve center in an active state, tending to discharge into a certain lower motor center, but unable to do so because a peripheral stimulus is necessary, in addition, in order to arouse this lower center. Then we find the higher center discharging intootherlower centers, and so giving rise to preparatory reactions. More precisely, what we find is that the higher center facilitates the response{84}of certain lower centers to their proper peripheral stimuli, while inhibiting the response of other lower centers to their appropriate stimuli. This is the same sort of thing that we observe in all control exerted by a higher center over a lower. It means that the higher center, besides its main line of connection with the lower center that will give the end-reaction, has minor lines of connection with certain other lower centers; some of these centers it facilitates and others it inhibits. These connections between the main and the subordinate centers may have been established by inborn nature, or by previous training, as will be explained in later chapters.
The action of the main center on the subordinate centers concerned in executing preparatory reactions does not relieve the tension in the main center. The dammed-up energy stays there till the proper stimulus is procured for arousing the end-reaction, and then escapes through its main channel of discharge, and the main center then finally comes to rest.
It may fairly be urged that no violence has been done to the general conception of a reaction by these additions, and also that with the additions the notion of a reaction has room for tendencies or inner adjustments. So that we conclude that stimulus-response psychology is adequate to the job, and will do justice to all forms of human behavior. It has a place for sensations, perceptions and thoughts, as we saw in the preceding chapter, and it has a place also for purposes, desires and motives generally.
In the present chapter, desirous of "keeping close to the ground", we have said little of distinctively human motives. That will come later. In general, a motive is a tendency towards a certain end-result or end-reaction, a tendency which is itself aroused by some stimulus, and which{85}persists for a time because its end-reaction is not at once made. The end-reaction is not made at once because it can only be aroused by an appropriate stimulus, acting in conjunction with the motive. But the motive, persisting in its inner activity, facilitates reactions to certain stimuli and inhibits others. The reactions it facilitates are preparatory to the end-reaction, in that they provide the necessary conditions for that reaction to occur, which means that they bring to bear on the individual the necessary stimulus which can arouse the end-reaction. The restlessness that characterizes an individual driven by an inner motive gives way to rest and satisfaction when the end-result is reached.
Motives range from the primitive or primal, like hunger, to the very advanced, such as zeal for a cause. They range from the momentary, illustrated by the need for more light in reading, to the great permanent forces of life, likeamour propreandesprit de corps. But the permanent motives are not always active; they sleep and are awakened again by appropriate stimuli.
In everyday speech we are apt to use the words "motive" and "reason" interchangeably, as in asking some one what his "motive", or what his "reason" is for doing so and so. A motive, however, is not necessarily a reason, nor a reason a motive. A reason is thought-out and conscious, which a motive need not be. On the other hand, a reason does not become a motive unless it takes hold of us and arouses a genuine tendency towards the planned result. You may prove to me, logically, the desirability of a course of action, but your reasons do not necessarily make me desire it. You can give a child excellent reasons for studying his lessons, but you have to stir some real motive of child life in order to get action. In the highest type of conduct, to be sure, motive and reason pull together, reason showing the way to the goal at which motive is aimed.