The Principles of Psychology, Volume 1 (of 2)

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A most interesting effect of cortical disorder is mental blindness. This consists not so much in insensibility to optical impressions, as in inability to understand them. Psychologically it is interpretable as loss of associations between optical sensations and what they signify; and any interruption of the paths between the optic centres and the centres for other ideas ought to bring it about. Thus, printed letters of the alphabet, or words, signify certain sounds and certain articulatory movements. If the connection between the articulating or auditory centres, on the one hand, and the visual centres on the other, be ruptured we ought a priori to expect that the sight of words would fail to awaken the idea of their sound, or the movement for pronouncing them. We ought, in short, to have alexia, or inability to read: and this is just what we do have in many cases of extensive injury about the fronto-temporal regions, as a complication of aphasic disease. Nothnagel suggests that whilst the cuneus is the seat of optical sensations, the other parts of the occipital lobe may be the field of optical memories and ideas, from the loss of which mental blindness should ensue. In fact, all the medical authors speak of mental blindness as if it must consist in the loss of visual images from the memory. It seems to me, however, that this is a psychological misapprehension. A man whose power of visual imagination has decayed (no unusual phenomenon in its lighter grades) is not mentally blind in the least, for he recognizes perfectly all that he sees. On the other hand, he may be mentally blind, with his optical imagination well preserved; as in the interesting case published by Wilbrand in 1887.[26] In the still more interesting case of mental blindness recently published by Lissauer,[27] though the patient made the most ludicrous mistakes, calling for instance a clothes-brush a pair of spectacles, an umbrella a plant with flowers, an apple a portrait of a lady, etc. etc., he seemed, according to the reporter, to have his mental images fairly well preserved. It is in fact the momentary loss of our non-optical images which makes us mentally blind, just as it is that of our non-auditory images which makes us mentally deaf. I am mentally deaf if, hearing a bell, I can't recall how it looks; and mentally blind if, seeing it, I can't recall its sound or its name. As a matter of fact, I should have to be not merely mentally blind, but stone-blind, if all my visual images were lost. For although I am blind to the right half of the field of view if my left occipital region is injured, and to the left half if my right region is injured, such hemianopsia does not deprive me of visual images, experience seeming to show that the unaffected hemisphere is always sufficient for production of these.To abolish them entirely I should have to be deprived of both occipital lobes, and that would deprive me not only of my inward images of sight, but of my sight altogether.[28] Recent pathological annals seem to offer a few such cases.[29] Meanwhile there are a number of cases of mental blindness, especially for written language, coupled with hemianopsia, usually of the rightward field of view. These are all explicable by the breaking down, through disease, of the connecting tracts between the occipital lobes and other parts of the brain, especially those which go to the centres for speech in the frontal and temporal regions of the left hemisphere. They are to be classed among disturbances of conduction or of association; and nowhere can I find any fact which should force us to believe that optical images need[30] be lost in mental blindness, or that the cerebral centres for such images are locally distinct from those for direct sensations from the eyes.[31]

Where an object fails to be recognized by sight, it often happens that the patient will recognize and name it as soon as he touches it with his hand.This shows in an interesting way how numerous the associative paths are which all end by running out of the brain through the channel of speech. The hand-path is open, though the eye-path be closed. When mental blindness is most complete, neither sight, touch, nor sound avails to steer the patient, and a sort of dementia which has been called asymbolia or apraxia is the result. The commonest articles are not understood. The patient will put his breeches on one shoulder and his hat upon the other, will bite into the soap and lay his shoes on the table, or take his food into his hand and throw it down again, not knowing what to do with it, etc. Such disorder can only come from extensive brain-injury.[32]

The method of degeneration corroborates the other evidence localizing the tracts of vision. In young animals one gets secondary degeneration of the occipital regions from destroying an eyeball, and, vice versâ, degeneration of the optic nerves from destroying the occipital regions.The corpora geniculata, thalami, and subcortical fibres leading to the occipital lobes are also found atrophied in these cases.The phenomena are not uniform, but are indisputable;[33] so that, taking all lines of evidence together, the special connection of vision with the occipital lobes is perfectly made out. It should be added, that the occipital lobes have frequently been found shrunken in cases of inveterate blindness in man.

Hearing.

Hearing is hardly as definitely localized as sight. In the dog, Luciani's diagram will show the regions which directly or indirectly affect it for the worse when injured.As with sight, one-sided lesions produce symptoms on both sides.The mixture of black dots and gray dots in the diagram is meant to represent this mixture of 'crossed' and 'uncrossed' connections, though of course no topographical exactitude is aimed at.Of all the region, the temporal lobe is the most important part; yet permanent absolute deafness did not result in a dog of Luciani's, even from bilateral destruction of both temporal lobes in their entirety.[34]

In the monkey, Ferrier and Yeo once found permanent deafness to follow destruction of the upper temporal convolution (the one just below the fissure of Sylvius in Fig.6) on both sides.Brown and Schaefer found, on the contrary, that in several monkeys this operation failed to noticeably affect the hearing.In one animal, indeed, both entire temporal lobes were destroyed.After a week or two of depression of the mental faculties this beast recovered and became one of the brightest monkeys possible, domineering over all his mates, and admitted by all who saw him to have all his senses, including hearing, 'perfectly acute.'[35] Terrible recriminations have, as usual, ensued between the investigators, Ferrier denying that Brown and Schaefer's ablations were complete,[36] Schaefer that Ferrier's monkey was really deaf.[37] In this unsatisfactory condition the subject must be left, although there seems no reason to doubt that Brown and Schaefer's observation is the more important of the two.

In man the temporal lobe is unquestionably the seat of the hearing function, and the superior convolution adjacent to the sylvian fissure is its most important part. The phenomena of aphasia show this. We studied motor aphasia a few pages back; we must now consider sensory aphasia Our knowledge of this disease has had three stages: we may talk of the period of Broca, the period of Wernicke, and the period of Charcot. What Broca's discovery was we have seen. Wernicke was the first to discriminate those cases in which the patient can not even understand speech from those in which he can understand, only not talk; and to ascribe the former condition to lesion of the temporal lobe.[38] The condition in question is word-deafness, and the disease is auditory aphasiaThe latest statistical survey of the subject is that by Dr. Allen Starr.[39] In the seven cases of pure word-deafness which he has collected, cases in which the patient could read, talk, and write, but not understand what was said to him, the lesion was limited to the first and second temporal convolutions in their posterior two thirds. The lesion (in right-handed, i.e. left-brained, persons) is always on the left side, like the lesion in motor aphasia. Crude hearing would not be abolished, even were the left centre for it utterly destroyed; the right centre would still provide for that. But the linguistic use of hearing appears bound up with the integrity of the left centre more or less exclusively. Here it must be that words heard enter into association with the things which they represent, on the one hand, and with the movements necessary for pronouncing them, on the other. In a large majority of Dr. Starr's fifty cases, the power either to name objects or to talk coherently was impaired. This shows that in most of us (as Wernicke said) speech must go on from auditory cues; that is, it must be that our ideas do not innervate our motor centres directly, but only after first arousing the mental sound of the words. This is the immediate stimulus to articulation; and where the possibility of this is abolished by the destruction of its usual channel in the left temporal lobe, the articulation must suffer. In the few cases in which the channel is abolished with no bad effect on speech we must suppose an idiosyncrasy. The patient must innervate his speech-organs either from the corresponding portion of the other hemisphere or directly from the centres of ideation, those, namely, of vision, touch, etc., without leaning on the auditory region. It is the minuter analysis of the facts in the light of such individual differences as these which constitutes Charcot's contribution towards clearing up the subject.

Every nameable thing, act, or relation has numerous properties, qualities, or aspects. In our minds the properties of each thing, together with its name, form an associated group. If different parts of the brain are severally concerned with the several properties, and a farther part with the hearing, and still another with the uttering, of the name, there must inevitably be brought about (through the law of association which we shall later study) such a dynamic connection amongst all these brain-parts that the activity of any one of them will be likely to awaken the activity of all the rest. When we are talking as we think, the ultimate process is that of utterance. If the brain-part for that be injured, speech is impossible or disorderly, even though all the other brain-parts be intact: and this is just the condition of things which, on page 37, we found to be brought about by limited lesion of the left inferior frontal convolution. But back of that last act various orders of succession are possible in the associations of a talking man's ideas. The more usual order seems to be from the tactile, visual, or other properties of the things thought-about to the sound of their names, and then to the latter's utterance. But if in a certain individual the thought of the look of an object or of the look of its printed name be the process which habitually precedes articulation, then the loss of the hearing centre will pro tanto not affect that individual's speech. He will be mentally deaf, i.e. his understanding of speech will suffer, but he will not be aphasic. In this way it is possible to explain the seven cases of pure word-deafness which figure in Dr. Starr's table.

If this order of association be ingrained and habitual in that individual, injury to his visual centres will make him not only word-blind, but aphasic as well. His speech will become confused in consequence of an occipital lesion. Naunyn, consequently, plotting out on a diagram of the hemisphere the 71 irreproachably reported cases of aphasia which he was able to collect, finds that the lesions concentrate themselves in three places: first, on Broca's centre; second, on Wernicke's; third, on the supra-marginal and angular gyri under which those fibres pass which connect the visual centres with the rest of the brain[40] (see Fig. 17). With this result Dr. Starr's analysis of purely sensory cases agrees.

In a later chapter we shall again return to these differences in the effectiveness of the sensory spheres in different individuals.Meanwhile few things show more beautifully than the history of our knowledge of aphasia how the sagacity and patience of many banded workers are in time certain to analyze the darkest confusion into an orderly display.[41] There is no 'centre of Speech' in the brain any more than there is a faculty of Speech in the mind. The entire brain, more or less, is at work in a man who uses language. The subjoined diagram, from Boss, shows the four parts most critically concerned, and, in the light of our text, needs no farther explanation (see Fig. 18).

Smell.

Everything conspires to point to the median descending part of the temporal lobes as being the organs of smell.Even Ferrier and Munk agree on the hippocampal gyrus, though Ferrier restricts olfaction, as Munk does not, to the lobule or uncinate process of the convolution, reserving the rest of it for touch.Anatomy and pathology also point to the hippocampal gyrus; but as the matter is less interesting from the point of view of human psychology than were sight and hearing, I will say no more, but simply add Luciani and Seppili's diagram of the dog's smell-centre.[42] Of

Taste

we know little that is definite.What little there is points to the lower temporal regions again.Consult Ferrier as below.

Touch.

Interesting problems arise with regard to the seat of tactile and muscular sensibility. Hitzig, whose experiments on dogs' brains fifteen years ago opened the entire subject which we are discussing, ascribed the disorders of motility observed after ablations of the motor region to a loss of what he called muscular consciousness. The animals do not notice eccentric positions of their limbs, will stand with their legs crossed, with the affected paw resting on its back or hanging over a table's edge, etc.; and do not resist our bending and stretching of it as they resist with the unaffected paw. Goltz, Munk, Schiff, Herzen, and others promptly ascertained an equal defect of cutaneous sensibility to pain, touch, and cold. The paw is not withdrawn when pinched, remains standing in cold water, etc. Ferrier meanwhile denied that there was any true anæsthesia produced by ablations in the motor zone, and explains the appearance of it as an effect of the sluggish motor responses of the affected side.[43] Munk[44] and Schiff[45], on the contrary, conceive of the 'motor zone' as essentially sensory, and in different ways explain the motor disorders as secondary results of the anæsthesia which is always there, Munk calls the motor zone the Fühlsphäre of the animal's limbs, etc., and makes it coördinate with the Sehsphäre, the Hörsphäre, etc., the entire cortex being, according to him, nothing but a projection-surface for sensations, with no exclusively or essentially motor part. Such a view would be important if true, through its bearings on the psychology of volition. What is the truth? As regards the fact of cutaneous anæsthesia from motor-zone ablations, all other observers are against Ferrier, so that he is probably wrong in denying it. On the other hand, Munk and Schiff are wrong in making the motor symptoms depend on the anæsthesia, for in certain rare cases they have been observed to exist not only without insensibility, but with actual hyperæsthesia of the parts.[46] The motor and sensory symptoms seem, therefore, to be independent variables.

In monkeys the latest experiments are those of Horsley and Schaefer,[47] whose results Ferrier accepts. They find that excision of the hippocampal convolution produces transient insensibility of the opposite side of the body, and that permanent insensibility is produced by destruction of its continuation upwards above the corpus callosum, the so-called gyrus fornicatus (the part just below the 'calloso-marginal fissure' in Fig. 7). The insensibility is at its maximum when the entire tract comprising both convolutions is destroyed. Ferrier says that the sensibility of monkeys is 'entirely unaffected' by ablations of the motor zone,[48] and Horsley and Schaefer consider it by no means necessarily abolished.[49] Luciani found it diminished in his three experiments on apes.[50]

In man we have the fact that one-sided paralysis from disease of the opposite motor zone may or may not be accompanied with anæsthesia of the parts. Luciani, who believes that the motor zone is also sensory, tries to minimize the value of this evidence by pointing to the insufficiency with which patients are examined. He himself believes that in dogs the tactile sphere extends backwards and forwards of the directly excitable region, into the frontal and parietal lobes (see Fig. 20). Nothnagel considers that pathological evidence points in the same direction;[51] and Dr. Mills, carefully reviewing the evidence, adds the gyri fornicatus and hippocampi to the cutaneo-muscular region in man.[52] If one compare Luciani's diagrams together (Figs. 14, 16, 19, 20) one will see that the entire parietal region of the dog's skull is common to the four senses of sight, hearing, smell, and touch, including muscular feeling. The corresponding region in the human brain (upper parietal and supra-marginal gyri—see Fig. 17) seems to be a somewhat similar place of conflux. Optical aphasias and motor and tactile disturbances all result from its injury, especially when that is on the left side.[53] The lower we go in the animal scale the less differentiated the functions of the several brain-parts seem to be.[54] It may be that the region in question still represents in ourselves something like this primitive condition, and that the surrounding parts, in adapting themselves more and more to specialized and narrow functions, have left it as a sort of carrefour through which they send currents and converse. That it should be connected with musculo-cutaneous feeling is, however, no reason why the motor zone proper should not be so connected too. And the cases of paralysis from the motor zone with no accompanying anæsthesia may be explicable without denying all sensory function to that region. For, as my colleague Dr. James Putnam informs me, sensibility is always harder to kill than motility, even where we know for a certainty that the lesion affects tracts that are both sensory and motor. Persons whose hand is paralyzed in its movements from compression of arm-nerves during sleep, still feel with their fingers; and they may still feel in their feet when their legs are paralyzed by bruising of the spinal cord. In a similar way, the motor cortex might be sensitive as well as motor, and yet by this greater subtlety (or whatever the peculiarity may be) in the sensory currents, the sensibility might survive an amount of injury there by which the motility was destroyed. Nothnagel considers that there are grounds for supposing the muscular sense to be exclusively connected with the parietal lobe and not with the motor zone. "Disease of this lobe gives pure ataxy without palsy, and of the motor zone pure palsy without loss of muscular sense."[55] He fails, however, to convince more competent critics than the present writer,[56] so I conclude with them that as yet we have no decisive grounds for locating muscular and cutaneous feeling apart. Much still remains to be learned about the relations between musculo-cutaneous sensibility and the cortex, but one thing is certain: that neither the occipital, the forward frontal, nor the temporal lobes seem to have anything essential to do with it in man. It is knit up with the performances of the motor zone and of the convolutions backwards and midwards of themThe reader must remember this conclusion when we come to the chapter on the Will.

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I must add a word about the connection of aphasia with the tactile sense. On p.40 I spoke of those cases in which the patient can write but not read his own writing. He cannot read by his eyes; but he can read by the feeling in his fingers, if he retrace the letters in the air. It is convenient for such a patient to have a pen in hand whilst reading in this way, in order to make the usual feeling of writing more complete.[57] In such a case we must suppose that the path between the optical and the graphic centres remains open, whilst that between the optical and the auditory and articulatory centres is closed. Only thus can we understand how the look of the writing should fail to suggest the sound of the words to the patient's mind, whilst it still suggests the proper movements of graphic imitation. These movements in their turn must of course be felt, and the feeling of them must be associated with the centres for hearing and pronouncing the words. The injury in cases like this where very special combinations fail, whilst others go on as usual, must always be supposed to be of the nature of increased resistance to the passage of certain currents of association. If any of the elements of mental function were destroyed the incapacity would necessarily be much more formidable. A patient who can both read and write with his fingers most likely uses an identical 'graphic' centre, at once sensory and motor, for both operations.

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I have now given, as far as the nature of this book will allow, a complete account of the present state of the localization-question.In its main outlines it stands firm, though much has still to be discovered.The anterior frontal lobes, for example, so far as is yet known, have no definite functions.Goltz finds that dogs bereft of them both are incessantly in motion, and excitable by every small stimulus.They are irascible and amative in an extraordinary degree, and their sides grow bare with perpetual reflex scratching; but they show no local troubles of either motion or sensibility. In monkeys not even this lack of inhibitory ability is shown, and neither stimulation nor excision of the prefrontal lobes produces any symptoms whatever. One monkey of Horsley and Schaefer's was as tame, and did certain tricks as well, after as before the operation.[58] It is probable that we have about reached the limits of what can be learned about brain-functions from vivisecting inferior animals, and that we must hereafter look more exclusively to human pathology for light. The existence of separate speech and writing centres in the left hemisphere in man; the fact that palsy from cortical injury is so much more complete and enduring in man and the monkey than in dogs; and the farther fact that it seems more difficult to get complete sensorial blindness from cortical ablations in the lower animals than in man, all show that functions get more specially localized as evolution goes on. In birds localization seems hardly to exist, and in rodents it is much less conspicuous than in carnivora. Even for man, however, Munk's way of mapping out the cortex into absolute areas within which only one movement or sensation is represented is surely false. The truth seems to be rather that, although there is a correspondence of certain regions of the brain to certain regions of the body, yet the several parts within each bodily region are represented throughout the whole of the corresponding brain-region like pepper and salt sprinkled from the same caster. This, however, does not prevent each 'part' from having its focus at one spot within the brain-region. The various brain-regions merge into each other in the same mixed way. As Mr. Horsley says: "There are border centres, and the area of representation of the face merges into that for the representation of the upper limb. If there was a focal lesion at that point, you would have the movements of these two parts starting together."[59] The accompanying figure from Paneth shows just how the matter stands in the dog.[60]

I am speaking now of localizations breadthwise over the brain-surface.It is conceivable that there might be also localizations depthwise through the cortex.The more superficial cells are smaller, the deepest layer of them is large; and it has been suggested that the superficial cells are sensorial, the deeper ones motor;[61] or that the superficial ones in the motor region are correlated with the extremities of the organs to be moved (fingers, etc.), the deeper ones with the more central segments (wrist, elbow, etc.).[62] It need hardly be said that all such theories are as yet but guesses.

We thus see that the postulate of Meynert and Jackson which we started with on p.30 is on the whole most satisfactorily corroborated by subsequent objective research. The highest centres do probably contain nothing but arrangements for representing impressions and movements, and other arrangements for coupling the activity Of these arrangements together.[63] Currents pouring in from the sense-organs first excite some arrangements, which in turn excite others, until at last a motor discharge downwards of some sort occurs. When this is once clearly grasped there remains little ground for keeping up that old controversy about the motor zone, as to whether it is in reality motor or sensitive. The whole cortex, inasmuch as currents run through it, is both. All the currents probably have feelings going with them, and sooner or later bring movements about. In one aspect, then, every centre is afferent, in another efferent, even the motor cells of the spinal cord having these two aspects inseparably conjoined. Marique,[64] and Exner and Paneth[65] have shown that by cutting round a 'motor' centre and so separating it from the influence of the rest of the cortex, the same disorders are produced as by cutting it out, so that really it is only the mouth of the funnel, as it were, through which the stream of innervation, starting from elsewhere, pours;[66] consciousness accompanying the stream, and being mainly of things seen if the stream is strongest occipitally, of things heard if it is strongest temporally, of things felt, etc., if the stream occupies most intensely the 'motor zone.' It seems to me that some broad and vague formulation like this is as much as we can safely venture on in the present state of science; and in subsequent chapters I expect to give confirmatory reasons for my view.

MAN'S CONSCIOUSNESS LIMITED TO THE HEMISPHERES.

But is the consciousness which accompanies the activity of the cortex the only consciousness that man has? or are his lower centres conscious as well?

This is a difficult question to decide, how difficult one only learns when one discovers that the cortex-consciousness itself of certain objects can be seemingly annihilated in any good hypnotic subject by a bare wave of his operator's hand, and yet be proved by circumstantial evidence to exist all the while in a split-off condition, quite as 'ejective'[67] to the rest of the subject's mind as that mind is to the mind of the bystanders.[68] The lower centres themselves may conceivably all the while have a split-off consciousness of their own, similarly ejective to the cortex-consciousness; but whether they have it or not can never be known from merely introspective evidence. Meanwhile the fact that occipital destruction in man may cause a blindness which is apparently absolute (no feeling remaining either of light or dark over one half of the field of view), would lead us to suppose that if our lower optical centres, the corpora quadrigemina, and thalami, do have any consciousness, it is at all events a consciousness which does not mix with that which accompanies the cortical activities, and which has nothing to do with our personal Self. In lower animals this may not be so much the case. The traces of sight found (supra, p.46) in dogs and monkeys whose occipital lobes were entirely destroyed, may possibly have been due to the fact that the lower centres of these animals saw, and that what they saw was not ejective but objective to the remaining cortex, i.e. it formed part of one and the same inner world with the things which that cortex perceived. It may be, however, that the phenomena were due to the fact that in these animals the cortical 'centres' for vision reach outside of the occipital zone, and that destruction of the latter fails to remove them as completely as in man. This, as we know, is the opinion of the experimenters themselves. For practical purposes, nevertheless, and limiting the meaning of the word consciousness to the personal self of the individual, we can pretty confidently answer the question prefixed to this paragraph by saying that the cortex is the sole organ of consciousness in man[69] If there be any consciousness pertaining to the lower centres, it is a consciousness of which the self knows nothing.

THE RESTITUTION OF FUNCTION.

Another problem, not so metaphysical, remains. The most general and striking fact connected with cortical injury is that of the restoration of function. Functions lost at first are after a few days or weeks restored. How are we to understand this restitution?

Two theories are in the field:

1) Restitution is due to the vicarious action either of the rest of the cortex or of centres lower down, acquiring functions which until then they had not performed;

2) It is due to the remaining centres (whether cortical or 'lower') resuming functions which they had always had, but of which the wound had temporarily inhibited the exercise.This is the view of which Goltz and Brown-Séquard are the most distinguished defenders.

Inhibition is a vera causa, of that there can be no doubt.The pneumogastric nerve inhibits the heart, the splanchnic inhibits the intestinal movements, and the superior laryngeal those of inspiration.The nerve-irritations which may inhibit the contraction of arterioles are innumerable, and reflex actions are often repressed by the simultaneous excitement of other sensory nerves.For all such facts the reader must consult the treatises on physiology.What concerns us here is the inhibition exerted by different parts of the nerve-centres, when irritated, on the activity of distant parts.The flaccidity of a frog from 'shock,' for a minute or so after his medulla oblongata is cut, is an inhibition from the seat of injury which quickly passes away.

What is known as 'surgical shock '(unconsciousness, pallor, dilatation of splanchnic blood-vessels, and general syncope and collapse) in the human subject is an inhibition which lasts a longer time.Goltz, Freusberg, and others, cutting the spinal cord in dogs, proved that there were functions inhibited still longer by the wound, but which re-established themselves ultimately if the animal was kept alive.The lumbar region of the cord was thus found to contain independent vaso-motor centres, centres for erection, for control of the sphincters, etc., which could be excited to activity by tactile stimuli and as readily reinhibited by others simultaneously applied.[70] We may therefore plausibly suppose that the rapid reappearance of motility, vision, etc., after their first disappearance in consequence of a cortical mutilation, is due to the passing off of inhibitions exerted by the irritated surface of the wound. The only question is whether all restorations of function must be explained in this one simple way, or whether some part of them may not be owing to the formation of entirely new paths in the remaining centres, by which they become 'educated' to duties which they did not originally possess. In favor of an indefinite extension of the inhibition theory facts may be cited such as the following: In dogs whose disturbances due to cortical lesion have disappeared, they may in consequence of some inner or outer accident reappear in all their intensity for 24 hours or so and then disappear again.[71] In a dog made half blind by an operation, and then shut up in the dark, vision comes back just as quickly as in other similar dogs whose sight is exercised systematically every day.[72] A dog which has learned to beg before the operation recommences this practice quite spontaneously a week after a double-sided ablation of the motor zone.[73] Occasionally, in a pigeon (or even, it is said, in a dog) we see the disturbances less marked immediately after the operation than they are half an hour later.[74] This would be impossible were they due to the subtraction of the organs which normally carried them on. Moreover the entire drift of recent physiological and pathological speculation is towards enthroning inhibition as an ever-present and indispensable condition of orderly activity. We shall see how great is its importance, in the chapter on the Will. Mr. Charles Mercier considers that no muscular contraction, once begun, would ever stop without it, short of exhaustion of the system;[75] and Brown-Séquard has for years been accumulating examples to show how far its influence extends.[76] Under these circumstances it seems as if error might more probably lie in curtailing its sphere too much than in stretching it too far as an explanation of the phenomena following cortical lesion.[77]

On the other hand, if we admit no re-education of centres, we not only fly in the face of an a priori probability, but we find ourselves compelled by facts to suppose an almost incredible number of functions natively lodged in the centres below the thalami or even in those below the corpora quadrigemina. I will consider the a priori objection after first taking a look at the facts which I have in mind. They confront us the moment we ask ourselves just which are the parts which perform the functions abolished by an operation after sufficient time has elapsed for restoration to occur?

The first observers thought that they must be the corresponding parts of the opposite or intact hemisphereBut as long ago as 1875 Carville and Duret tested this by cutting out the fore-leg-centre on one side, in a dog, and then, after waiting till restitution had occurred, cutting it out on the opposite side as well.Goltz and others have done the same thing.[78] If the opposite side were really the seat of the restored function, the original palsy should have appeared again and been permanent. But it did not appear at all; there appeared only a palsy of the hitherto unaffected side. The next supposition is that the parts surrounding the cut-out region learn vicariously to perform its duties. But here, again, experiment seems to upset the hypothesis, so far as the motor zone goes at least; for we may wait till motility has returned in the affected limb, and then both irritate the cortex surrounding the wound without exciting the limb to movement, and ablate it, without bringing back the vanished palsy.[79] It would accordingly seem that the cerebral centres below the cortex must be the seat of the regained activities. But Goltz destroyed a dog's entire left hemisphere, together with the corpus striatum and the thalamus on that side, and kept him alive until a surprisingly small amount of motor and tactile disturbance remained.[80] These centres cannot here have accounted for the restitution. He has even, as it would appear,[81] ablated both the hemispheres of a dog, and kept him alive 51 days, able to walk and stand. The corpora striata and thalami in this dog were also practically gone. In view of such results we seem driven, with M. François-Franck,[82] to fall back on the ganglia lower still, or even on the spinal cord as the 'vicarious' organ of which we are in quest. If the abeyance of function between the operation and the restoration was due exclusively to inhibition, then we must suppose these lowest centres to be in reality extremely accomplished organs. They must always have done what we now find them doing after function is restored, even when the hemispheres were intact. Of course this is conceivably the case; yet it does not seem very plausible. And the a priori considerations which a moment since I said I should urge, make it less plausible still.

For, in the first place, the brain is essentially a place of currents, which run in organized paths.Loss of function can only mean one of two things, either that a current can no longer run in, or that if it runs in, it can no longer run out, by its old path.Either of these inabilities may come from a local ablation; and 'restitution' can then only mean that, in spite of a temporary block, an inrunning current has at last become enabled to flow out by its old path again—e.g., the sound of 'give your paw' discharges after some weeks into the same canine muscles into which it used to discharge before the operation. As far as the cortex itself goes, since one of the purposes for which it actually exists is the production of new paths,[83] the only question before us is: Is the formation of these particular 'vicarious' paths too much to expect of its plastic powers? It would certainly be too much to expect that a hemisphere should receive currents from optic fibres whose arriving-place within it is destroyed, or that it should discharge into fibres of the pyramidal strand if their place of exit is broken down. Such lesions as these must be irreparable within that hemisphere. Yet even then, through the other hemisphere, the corpus callosum, and the bilateral connections in the spinal cord, one can imagine some road by which the old muscles might eventually be innervated by the same incoming currents which innervated them before the block. And for all minor interruptions, not involving the arriving-place of the 'cortico-petal' or the place of exit of the 'cortico-fugal' fibres, roundabout paths of some sort through the affected hemisphere itself must exist, for every point of it is, remotely at least, in potential communication with every other point. The normal paths are only paths of least resistance. If they get blocked or cut, paths formerly more resistant become the least resistant paths under the changed conditions. It must never be forgotten that a current that runs in has got to run out somewhere; and if it only once succeeds by accident in striking into its old place of exit again, the thrill of satisfaction which the consciousness connected with the whole residual brain then receives will reinforce and fix the paths of that moment and make them more likely to be struck into again.The resultant feeling that the old habitual act is at last successfully back again, becomes itself a new stimulus which stamps all the existing currents in.It is matter of experience that such feelings of successful achievement do tend to fix in our memory whatever processes have led to them; and we shall have a good deal more to say upon the subject when we come to the Chapter on the Will.

My conclusion then is this: that some of the restitution of function (especially where the cortical lesion is not too great) is probably due to genuinely vicarious function on the part of the centres that remain; whilst some of it is due to the passing off of inhibitions.In other words, both the vicarious theory and the inhibition theory are true in their measure.But as for determining that measure, or saying which centres are vicarious, and to what extent they can learn new tricks, that is impossible at present.

FINAL CORRECTION OF THE MEYNERT SCHEME.

And now, after learning all these facts, what are we to think of the child and the candle-flame, and of that scheme which provisionally imposed itself on our acceptance after surveying the actions of the frog?(Cf. pp.25-6, supra.) It will be remembered that we then considered the lower centres en masse as machines for responding to present sense-impressions exclusively, and the hemispheres as equally exclusive organs of action from inward considerations or ideas; and that, following Meynert, we supposed the hemispheres to have no native tendencies to determinate activity, but to be merely superadded organs for breaking up the various reflexes performed by the lower centres, and combining their motor and sensory elements in novel ways. It will also be remembered that I prophesied that we should be obliged to soften down the sharpness of this distinction after we had completed our survey of the farther facts. The time has now come for that correction to be made.

Wider and completer observations show us both that the lower centres are more spontaneous, and that the hemispheres are more automatic, than the Meynert scheme allows.Schrader's observations in Goltz's Laboratory on hemisphereless frogs[84] and pigeons[85] give an idea quite different from the picture of these creatures which is classically current. Steiner's[86] observations on frogs already went a good way in the same direction, showing, for example, that locomotion is a well-developed function of the medulla oblongata. But Schrader, by great care in the operation, and by keeping the frogs a long time alive, found that at least in some of them the spinal cord would produce movements of locomotion when the frog was smartly roused by a poke, and that swimming and croaking could sometimes be performed when nothing above the medulla oblongata remained.[87] Schrader's hemisphereless frogs moved spontaneously, ate flies, buried themselves in the ground, and in short did many things which before his observations were supposed to be impossible unless the hemispheres remained. Steiner[88] and Vulpian have remarked an even greater vivacity in fishes deprived of their hemispheres. Vulpian says of his brainless carps[89] that three days after the operation one of them darted at food and at a knot tied on the end of a string, holding the latter so tight between his jaws that his head was drawn out of water. Later, "they see morsels of white of egg; the moment these sink through the water in front of them, they follow and seize them, sometimes after they are on the bottom, sometimes before they have reached it. In capturing and swallowing this food they execute just the same movements as the intact carps which are in the same aquarium. The only difference is that they seem to see them at less distance, seek them with less impetuosity and less perseverance in all the points of the bottom of the aquarium, but they struggle (so to speak) sometimes with the sound carps to grasp the morsels. It is certain that they do not confound these bits of white of egg with other white bodies, small pebbles for example, which are at the bottom of the water. The same carp which, three days after operation, seized the knot on a piece of string, no longer snaps at it now, but if one brings it near her, she draws away from it by swimming backwards before it comes into contact with her mouth."[90] Already on pp.9-10, as the reader may remember, we instanced those adaptations of conduct to new conditions, on the part of the frog's spinal cord and thalami, which led Pflüger and Lewes on the one hand and Goltz on the other to locate in these organs an intelligence akin to that of which the hemispheres are the seat.

When it comes to birds deprived of their hemispheres, the evidence that some of their acts have conscious purpose behind them is quite as persuasive.In pigeons Schrader found that the state of somnolence lasted only three or four days, after which time the birds began indefatigably to walk about the room.They climbed out of boxes in which they were put, jumped over or flew up upon obstacles, and their sight was so perfect that neither in walking nor flying did they ever strike any object in the room.They had also definite ends or purposes, flying straight for more convenient perching places when made uncomfortable by movements imparted to those on which they stood; and of several possible perches they always chose the most convenient."If we give the dove the choice of a horizontal bar (Reck) or an equally distant table to fly to, she always gives decided preference to the table.Indeed she chooses the table even if it is several meters farther off than the bar or the chair."Placed on the back of a chair, she flies first to the seat and then to the floor, and in general "will forsake a high position, although it give her sufficiently firm support, and in order to reach the ground will make use of the environing objects as intermediate goals of flight, showing a perfectly correct judgment of their distance.Although able to fly directly to the ground, she prefers to make the journey in successive stages....Once on the ground, she hardly ever rises spontaneously into the air."[91]

Young rabbits deprived of their hemispheres will stand, run, start at noises, avoid obstacles in their path, and give responsive cries of suffering when hurt. Rats will do the same, and throw themselves moreover into an attitude of defence. Dogs never survive such an operation if performed at once. But Goltz's latest dog, mentioned on p.70, which is said to have been kept alive for fifty-one days after both hemispheres had been removed by a series of ablations and the corpora striata and thalami had softened away, shows how much the mid-brain centres and the cord can do even in the canine species. Taken together, the number of reactions shown to exist in the lower centres by these observations make out a pretty good case for the Meynert scheme, as applied to these lower animals. That scheme demands hemispheres which shall be mere supplements or organs of repetition, and in the light of these observations they obviously are so to a great extent. But the Meynert scheme also demands that the reactions of the lower centres shall all be native, and we are not absolutely sure that some of those which we have been considering may not have been acquired after the injury; and it furthermore demands that they should be machine-like, whereas the expression of some of them makes us doubt whether they may not be guided by an intelligence of low degree.

Even in the lower animals, then, there is reason to soften down that opposition between the hemispheres and the lower centres which the scheme demands.The hemispheres may, it is true, only supplement the lower centres, but the latter resemble the former in nature and have some small amount at least of 'spontaneity' and choice.

But when we come to monkeys and man the scheme well-nigh breaks down altogether; for we find that the hemispheres do not simply repeat voluntarily actions which the lower centres perform as machines.There are many functions which the lower centres cannot by themselves perform at all.When the motor cortex is injured in a man or a monkey genuine paralysis ensues, which in man is incurable, and almost or quite equally so in the ape.Dr. Seguin knew a man with hemi-blindness, from cortical injury, which had persisted unaltered for twenty-three years.'Traumatic inhibition' cannot possibly account for this.The blindness must have been an 'Ausfallserscheinung,' due to the loss of vision's essential organ.It would seem, then, that in these higher creatures the lower centres must be less adequate than they are farther down in the zoological scale; and that even for certain elementary combinations of movement and impression the co-operation of the hemispheres is necessary from the start. Even in birds and dogs the power of eating properly is lost when the frontal lobes are cut off.[92]

The plain truth is that neither in man nor beast are the hemispheres the virgin organs which our scheme called them.So far from being unorganized at birth, they must have native tendencies to reaction of a determinate sort.[93] These are the tendencies which we know as emotions and instincts, and which we must study with some detail in later chapters of this book. Both instincts and emotions are reactions upon special sorts of objects of perception; they depend on the hemispheres; and they are in the first instance reflex, that is, they take place the first time the exciting object is met, are accompanied by no forethought or deliberation, and are irresistible. But they are modifiable to a certain extent by experience, and on later occasions of meeting the exciting object, the instincts especially have less of the blind impulsive character which they had at first. All this will be explained at some length in Chapter XXIV. Meanwhile we can say that the multiplicity of emotional and instinctive reactions in man, together with his extensive associative power, permit of extensive recouplings of the original sensory and motor partners. The consequences of one instinctive reaction often prove to be the inciters of an opposite reaction, and being suggested on later occasions by the original object, may then suppress the first reaction altogether, just as in the case of the child and the flame. For this education the hemispheres do not need to be tabulæ rasæ at first, as the Meynert scheme would have them; and so far from their being educated by the lower centres exclusively, they educate themselves.[94]

We have already noticed the absence of reactions from fear and hunger in the ordinary brainless frog. Schrader gives a striking account of the instinctless condition of his brainless pigeons, active as they were in the way of locomotion and voice. "The hemisphereless animal moves in a world of bodies which ... are all of equal value for him.... He is, to use Goltz's apt expression, impersonal....Every object is for him only a space-occupying mass, he turns out of his path for an ordinary pigeon no otherwise than for a stone.He may try to climb over both.All authors agree that they never found any difference, whether it was an inanimate body, a cat, a dog, or a bird of prey which came in their pigeon's way.The creature knows neither friends nor enemies, in the thickest company it lives like a hermit.The languishing cooing of the male awakens no more impression than the rattling of the peas, or the call-whistle which in the days before the injury used to make the birds hasten to be fed.Quite as little as the earlier observers have I seen hemisphereless she-birds answer the courting of the male.A hemisphereless male will coo all day long and show distinct signs of sexual excitement, but his activity is without any object, it is entirely indifferent to him whether the she-bird be there or not.If one is placed near him, he leaves her unnoticed....As the male pays no attention to the female, so she pays none to her young.The brood may follow the mother ceaselessly calling for food, but they might as well ask it from a stone....The hemisphereless sphereless pigeon is in the highest degree tame, and fears man as little as cat or bird of prey."[95]

Putting together now all the facts and reflections which we have been through, it seems to me that we can no longer hold strictly to the Meynert schemeIf anywhere, it will apply to the lowest animals; but in them especially the lower centres seem to have a degree of spontaneity and choice.On the whole, I think that we are driven to substitute for it some such general conception as the following, which allows for zoological differences as we know them, and is vague and elastic enough to receive any number of future discoveries of detail.

CONCLUSION.

All the centres, in all animals, whilst they are in one aspect mechanisms, probably are, or at least once were, organs of consciousness in another, although the consciousness is doubtless much more developed in the hemispheres than it is anywhere else. The consciousness must everywhere prefer some of the sensations which it gets to others; and if it can remember these in their absence, however dimly, they must be its ends of desire. If, moreover, it can identify in memory any motor discharges which may have led to such ends, and associate the latter with them, then these motor discharges themselves may in turn become desired as means. This is the development of will; and its realization must of course be proportional to the possible complication of the consciousness.Even the spinal cord may possibly have some little power of will in this sense, and of effort towards modified behavior in consequence of new experiences of sensibility.[96]

All nervous centres have then in the first instance one essential function, that of 'intelligent' action. They feel, prefer one thing to another, and have 'ends.' Like all other organs, however, they evolve from ancestor to descendant, and their evolution takes two directions, the lower centres passing downwards into more unhesitating automatism, and the higher ones upwards into larger intellectuality.[97] Thus it may happen that those functions which can safely grow uniform and fatal become least accompanied by mind, and that their organ, the spinal cord, becomes a more and more soulless machine; whilst on the contrary those functions which it benefits the animal to have adapted to delicate environing variations pass more and more to the hemispheres, whose anatomical structure and attendant consciousness grow more and more elaborate as zoological evolution proceeds. In this way it might come about that in man and the monkeys the basal ganglia should do fewer things by themselves than they can do in dogs, fewer in dogs than in rabbits, fewer in rabbits than in hawks,[98] fewer in hawks than in pigeons, fewer in pigeons than in frogs, fewer in frogs than in fishes, and that the hemispheres should correspondingly do more. This passage of functions forward to the ever-enlarging hemispheres would be itself one of the evolutive changes, to be explained like the development of the hemispheres themselves, either by fortunate variation or by inherited effects of use. The reflexes, on this view, upon which the education of our human hemispheres depends, would not be due to the basal ganglia alone. They would be tendencies in the hemispheres themselves, modifiable by education, unlike the reflexes of the medulla oblongata, pons, optic lobes and spinal cord. Such cerebral reflexes, if they exist, form a basis quite as good as that which the Meynert scheme offers, for the acquisition of memories and associations which may later result in all sorts of 'changes of partners' in the psychic world. The diagram of the baby and the candle (see page 25) can be re-edited, if need be, as an entirely cortical transaction.The original tendency to touch will be a cortical instinct; the burn will leave an image in another part of the cortex, which, being recalled by association, will inhibit the touching tendency the next time the candle is perceived, and excite the tendency to withdraw—so that the retinal picture will, upon that next time, be coupled with the original motor partner of the pain.We thus get whatever psychological truth the Meynert scheme possesses without entangling ourselves on a dubious anatomy and physiology.

Some such shadowy view of the evolution of the centres, of the relation of consciousness to them, and of the hemispheres to the other lobes, is, it seems to me, that in which it is safest to indulge.If it has no other advantage, it at any rate makes us realize how enormous are the gaps in our knowledge, the moment we try to cover the facts by any one formula of a general kind.

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CHAPTER III.

ON SOME GENERAL CONDITIONS OF BRAIN-ACTIVITY.

The elementary properties of nerve-tissue on which the brain-functions depend are far from being satisfactorily made out. The scheme that suggests itself in the first instance to the mind, because it is so obvious, is certainly false: I mean the notion that each cell stands for an idea or part of an idea, and that the ideas are associated or 'bound into bundles' (to use a phrase of Locke's) by the fibres. If we make a symbolic diagram on a blackboard, of the laws of association between ideas, we are inevitably led to draw circles, or closed figures of some kind, and to connect them by lines. When we hear that the nerve-centres contain cells which send off fibres, we say that Nature has realized our diagram for us, and that the mechanical substratum of thought is plain. In some way, it is true, our diagram must be realized in the brain; but surely in no such visible and palpable way as we at first suppose.[99] An enormous number of the cellular bodies in the hemispheres are fibreless. Where fibres are sent off they soon divide into untraceable ramifications; and nowhere do we see a simple coarse anatomical connection, like a line on the blackboard, between two cells. Too much anatomy has been found to order for theoretic purposes, even by the anatomists; and the popular-science notions of cells and fibres are almost wholly wide of the truth. Let us therefore relegate the subject of the intimate workings of the brain to the physiology of the future, save in respect to a few points of which a word must now be said. And first of

THE SUMMATION OF STIMULI

in the same nerve-tract.This is a property extremely important for the understanding of a great many phenomena of the neural, and consequently of the mental, life; and it behooves us to gain a clear conception of what it means before we proceed any farther.

The law is this, that a stimulus which would be inadequate by itself to excite a nerve-centre to effective discharge may, by acting with one or more other stimuli (equally ineffectual by themselves alone) bring the discharge aboutThe natural way to consider this is as a summation of tensions which at last overcome a resistance.The first of them produce a 'latent excitement' or a 'heightened irritability'—the phrase is immaterial so far as practical consequences go; the last is the straw which breaks the camel's back.Where the neural process is one that has consciousness for its accompaniment, the final explosion would in all cases seem to involve a vivid state of feeling of a more or less substantive kind.But there is no ground for supposing that the tensions whilst yet submaximal or outwardly ineffective, may not also have a share in determining the total consciousness present in the individual at the time.In later chapters we shall see abundant reason to suppose that they do have such a share, and that without their contribution the fringe of relations which is at every moment a vital ingredient of the mind's object, would not come to consciousness at all.

The subject belongs too much to physiology for the evidence to be cited in detail in these pages.I will throw into a note a few references for such readers as may be interested in following it out,[100] and simply say that the direct electrical irritation of the cortical centres sufficiently proves the point. For it was found by the earliest experimenters here that whereas it takes an exceedingly strong current to produce any movement when a single induction-shock is used, a rapid succession of induction-shocks ('faradization') will produce movements when the current is comparatively weak. A single quotation from an excellent investigation will exhibit this law under further aspects:

"If we continue to stimulate the cortex at short intervals with the strength of current which produces the minimal muscular contraction [of the dog's digital extensor muscle], the amount of contraction gradually increases till it reaches the maximum.Each earlier stimulation leaves thus an effect behind it, which increases the efficacy of the following one.In this summation of the stimuli....the following points may be noted: 1) Single stimuli entirely inefficacious when alone may become efficacious by sufficiently rapid reiteration.If the current used is very much less than that which provokes the first beginning of contraction, a very large number of successive shocks may be needed before the movement appears—20, 50, once 106 shocks were needed.2) The summation takes place easily in proportion to the shortness of the interval between the stimuli.A current too weak to give effective summation when its shocks are 3 seconds apart will be capable of so doing when the interval is shortened to 1 second.3) Not only electrical irritation leaves a modification which goes to swell the following stimulus, but every sort of irritant which can produce a contraction does so.If in any way a reflex contraction of the muscle experimented on has been produced, or if it is contracted spontaneously by the animal (as not unfrequently happens 'by sympathy,' during a deep inspiration), it is found that an electrical stimulus, until then inoperative, operates energetically if immediately applied."[101]

Furthermore:

"In a certain stage of the morphia-narcosis an ineffectively weak shock will become powerfully effective, if, immediately before its application to the motor centre, the skin of certain parts of the body is exposed to gentle tactile stimulation.... If, having ascertained the subminimal strength of current and convinced one's self repeatedly of its inefficacy, we draw our hand a single time lightly over the skin of the paw whose cortical centre is the object of stimulation, we find the current at once strongly effective. The increase of irritability lasts some seconds before it disappears. Sometimes the effect of a single light stroking of the paw is only sufficient to make the previously ineffectual current produce a very weak contraction. Repeating the tactile stimulation will then, as a rule, increase the contraction's extent."[102]

We constantly use the summation of stimuli in our practical appeals.If a car-horse balks, the final way of starting him is by applying a number of customary incitements at once.If the driver uses reins and voice, if one bystander pulls at his head, another lashes his hind quarters, and the conductor rings the bell, and the dismounted passengers shove the car, all at the same moment, his obstinacy generally yields, and he goes on his way rejoicing.If we are striving to remember a lost name or fact, we think of as many 'cues' as possible, so that by their joint action they may recall what no one of them can recall alone.The sight of a dead prey will often not stimulate a beast to pursuit, but if the sight of movement be added to that of form, pursuit occurs."Brücke noted that his brainless hen, which made no attempt to peck at the grain under her very eyes, began pecking if the grain were thrown on the ground with force, so as to produce a rattling sound."[103] "Dr. Allen Thomson hatched out some chickens on a carpet, where he kept them for several days. They showed no inclination to scrape,... but when Dr. Thomson sprinkled a little gravel on the carpet,... the chickens immediately began their scraping movements."[104] A strange person, and darkness, are both of them stimuli to fear and mistrust in dogs (and for the matter of that, in men). Neither circumstance alone may awaken outward manifestations, but together, i.e. when the strange man is met in the dark, the dog will be excited to violent defiance.[105] Street-hawkers well know the efficacy of summation, for they arrange themselves in a line upon the sidewalk, and the passer often buys from the last one of them, through the effect of the reiterated solicitation, what he refused to buy from the first in the row. Aphasia shows many examples of summation. A patient who cannot name an object simply shown him, will name it if he touches as well as sees it, etc.

Instances of summation might be multiplied indefinitely, but it is hardly worth while to forestall subsequent chapters.Those on Instinct, the Stream of Thought, Attention, Discrimination, Association, Memory, Æsthetics, and Will, will contain numerous exemplifications of the reach of the principle in the purely psychological field.

REACTION-TIME.

One of the lines of experimental investigation most diligently followed of late years is that of the ascertainment of the time occupied by nervous eventsHelmholtz led off by discovering the rapidity of the current in the sciatic nerve of the frog.But the methods he used were soon applied to the sensory nerves and the centres, and the results caused much popular scientific admiration when described as measurements of the 'velocity of thought.'The phrase 'quick as thought' had from time immemorial signified all that was wonderful and elusive of determination in the line of speed; and the way in which Science laid her doomful hand upon this mystery reminded people of the day when Franklin first 'eripuit cœlo fulmen,' foreshadowing the reign of a newer and colder race of gods. We shall take up the various operations measured, each in the chapter to which it more naturally pertains. I may say, however, immediately, that the phrase 'velocity of thought' is misleading, for it is by no means clear in any of the cases what particular act of thought occurs during the time which is measured. 'Velocity of nerve-action' is liable to the same criticism, for in most cases we do not know what particular nerve-processes occur. What the times in question really represent is the total duration of certain reactions upon stimuliCertain of the conditions of the reaction are prepared beforehand; they consist in the assumption of those motor and sensory tensions which we name the expectant state.Just what happens during the actual time occupied by the reaction (in other words, just what is added to the pre-existent tensions to produce the actual discharge) is not made out at present, either from the neural or from the mental point of view.

The method is essentially the same in all these investigations.A signal of some sort is communicated to the subject, and at the same instant records itself on a time-registering apparatus.The subject then makes a muscular movement of some sort, which is the 'reaction,' and which also records itself automatically.The time found to have elapsed between the two records is the total time of that observation.The time-registering instruments are of various types.One type is that of the revolving drum covered with smoked paper, on which one electric pen traces a line which the signal breaks and the 'reaction' draws again; whilst another electric pen (connected with a pendulum or a rod of metal vibrating at a known rate) traces alongside of the former line a 'time-line' of which each undulation or link stands for a certain fraction of a second, and against which the break in the reaction-line can be measured. Compare Fig. 21, where the line is broken by the signal at the first arrow, and continued again by the reaction at the second. Ludwig's Kymograph, Marey's Chronograph are good examples of this type of instrument.

Another type of instrument is represented by the stopwatch, of which the most perfect form is Hipp's Chronoscope.The hand on the dial measures intervals as short as 1/1000 of a second.The signal (by an appropriate electric connection) starts it; the reaction stops it; and by reading off its initial and terminal positions we have immediately and with no farther trouble the time we seek.A still simpler instrument, though one not very satisfactory in its working, is the 'psychodometer' of Exner & Obersteiner, of which I picture a modification devised by my colleague Professor H.P.Bowditch, which works very well.

The manner in which the signal and reaction are connected with the chronographic apparatus varies indefinitely in different experiments. Every new problem requires some new electric or mechanical disposition of apparatus.[106]

The least complicated time-measurement is that known as simple reaction-time, in which there is but one possible signal and one possible movement, and both are known in advance.The movement is generally the closing of an electric key with the hand.The foot, the jaw, the lips, even the eyelid, have been in turn made organs of reaction, and the apparatus has been modified accordingly.[107] The time usually elapsing between stimulus and movement lies between one and three tenths of a second, varying according to circumstances which will be mentioned anon.

The subject of experiment, whenever the reactions are short and regular, is in a state of extreme tension, and feels, when the signal comes, as if it started the reaction, by a sort of fatality, and as if no psychic process of perception or volition had a chance to intervene. The whole succession is so rapid that perception seems to be retrospective, and the time-order of events to be read off in memory rather than known at the moment. This at least is my own personal experience in the matter, and with it I find others to agree. The question is, What happens inside of us, either in brain or mind? and to answer that we must analyze just what processes the reaction involves. It is evident that some time is lost in each of the following stages:

1.The stimulus excites the peripheral sense-organ adequately for a current to pass into the sensory nerve;

2.The sensory nerve is traversed;

3.The transformation (or reflection) of the sensory into a motor current occurs in the centres;

4.The spinal cord and motor nerve are traversed;

5.The motor current excites the muscle to the contracting point.

Time is also lost, of course, outside the muscle, in the joints, skin, etc., and between the parts of the apparatus; and when the stimulus which serves as signal is applied to the skin of the trunk or limbs, time is lost in the sensorial conduction through the spinal cord.

The stage marked 3 is the only one that interests us here.The other stages answer to purely physiological processes, but stage 3 is psycho-physical; that is, it is a higher-central process, and has probably some sort of consciousness accompanying it.What sort?

Wundt has little difficulty in deciding that it is consciousness of a quite elaborate kind. He distinguishes between two stages in the conscious reception of an impression, calling one perception, and the other apperception, and likening the one to the mere entrance of an object into the periphery of the field of vision, and the other to its coming to occupy the focus or point of view. Inattentive awareness of an object, and attention to it, are, it seems to me, equivalents for perception and apperception, as Wundt uses the words. To these two forms of awareness of the impression Wundt adds the conscious volition to react, gives to the trio the name of 'psycho-physical' processes, and assumes that they actually follow upon each other in the succession in which they have been named.[108] So at least I understand him. The simplest way to determine the time taken up by this psycho-physical stage No. 3 would be to determine separately the duration of the several purely physical processes, 1, 2, 4, and 5, and to subtract them from the total reaction-time. Such attempts have been made.[109] But the data for calculation are too inaccurate for use, and, as Wundt himself admits,[110] the precise duration of stage 3 must at present be left enveloped with that of the other processes, in the total reaction-time.

My own belief is that no such succession of conscious feelings as Wundt describes takes place during stage 3. It is a process of central excitement and discharge, with which doubtless some feeling coexists, but what feeling we cannot tell, because it is so fugitive and so immediately eclipsed by the more substantive and enduring memory of the impression as it came in, and of the executed movement of response. Feeling of the impression, attention to it, thought of the reaction, volition to react, would, undoubtedly, all be links of the process under other conditions,[111] and would lead to the same reaction—after an indefinitely longer time. But these other conditions are not those of the experiments we are discussing; and it is mythological psychology (of which we shall see many later examples) to conclude that because two mental processes lead to the same result they must be similar in their inward subjective constitution. The feeling of stage 3 is certainly no articulate perception. It can be nothing but the mere sense of a reflex discharge. The reaction whose time is measured is, in short, a reflex action pure and simple, and not a psychic actA foregoing psychic condition is, it is true, a prerequisite for this reflex action.The preparation of the attention and volition; the expectation of the signal and the readiness of the hand to move, the instant it shall come; the nervous tension in which the subject waits, are all conditions of the formation in him for the time being of a new path or arc of reflex discharge.The tract from the sense-organ which receives the stimulus, into the motor centre which discharges the reaction, is already tingling with premonitory innervation, is raised to such a pitch of heightened irritability by the expectant attention, that the signal is instantaneously sufficient to cause the overflow.[112] No other tract of the nervous system is, at the moment, in this hair-trigger condition. The consequence is that one sometimes responds to a wrong signal, especially if it be an impression of the same kind with the signal we expect.[113] But if by chance we are tired, or the signal is unexpectedly weak, and we do not react instantly, but only after an express perception that the signal has come, and an express volition, the time becomes quite disproportionately long (a second or more, according to Exner[114]), and we feel that the process is in nature altogether different.

In fact, the reaction-time experiments are a case to which we can immediately apply what we have just learned about the summation of stimuli. 'Expectant attention' is but the subjective name for what objectively is a partial stimulation of a certain pathway, the pathway from the 'centre' for the signal to that for the discharge. In Chapter XI we shall see that all attention involves excitement from within of the tract concerned in feeling the objects to which attention is given. The tract here is the excito-motor arc about to be traversed. The signal is but the spark from without which touches off a train already laid. The performance, under these conditions, exactly resembles any reflex action. The only difference is that whilst, in the ordinarily so-called reflex acts, the reflex arc is a permanent result of organic growth, it is here a transient result of previous cerebral conditions.[115]

I am happy to say that since the preceding paragraphs (and the notes thereto appertaining) were written, Wundt has himself become converted to the view which I defend. He now admits that in the shortest reactions "there is neither apperception nor will, but that they are merely brain-reflexes due to practice."[116] The means of his conversion are certain experiments performed in his laboratory by Herr L. Lange,[117] who was led to distinguish between two ways of setting the attention in reacting on a signal, and who found that they gave very different time-results. In the 'extreme sensorial' way, as Lange calls it, of reacting, one keeps one's mind as intent as possible upon the expected signal, and 'purposely avoids'[118] thinking of the movement to be executed; in the 'extreme muscular' way one 'does not think at all'[119] of the signal, but stands as ready as possible for the movement. The muscular reactions are much shorter than the sensorial ones, the average difference being in the neighborhood of a tenth of a second. Wundt accordingly calls them 'shortened reactions' and, with Lange, admits them to be mere reflexes; whilst the sensorial reactions he calls 'complete,' and holds to his original conception as far as they are concerned. The facts, however, do not seem to me to warrant even this amount of fidelity to the original Wundtian position. When we begin to react in the 'extreme sensorial' way, Lange says that we get times so very long that they must be rejected from the count as non-typical. "Only after the reacter has succeeded by repeated and conscientious practice in bringing about an extremely precise co-ordination of his voluntary impulse with his sense-impression do we get times which can be regarded as typical sensorial reaction-times."[120] Now it seems to me that these excessive and 'untypical' times are probably the real 'complete times,' the only ones in which distinct processes of actual perception and volition occur (see above, pp.88-9).The typical sensorial time which is attained by practice is probably another sort of reflex, less perfect than the reflexes prepared by straining one's attention towards the movement.[121] The times are much more variable in the sensorial way than in the muscular. The several muscular reactions differ little from each other. Only in them does the phenomenon occur of reacting on a false signal, or of reacting before the signal. Times intermediate between these two types occur according as the attention fails to turn itself exclusively to one of the extremes. It is obvious that Herr Lange's distinction between the two types of reaction is a highly important one, and that the 'extreme muscular method,' giving both the shortest times and the most constant ones, ought to be aimed at in all comparative investigations. Herr Lange's own muscular time averaged 0''. 123; his sensorial time, 0''. 230.

These reaction-time experiments are then in no sense measurements of the swiftness of thoughtOnly when we complicate them is there a chance for anything like an intellectual operation to occur.They may be complicated in various ways.The reaction may be withheld until the signal has consciously awakened a distinct idea (Wundt's discrimination-time, association-time) and then performed.Or there may be a variety of possible signals, each with a different reaction assigned to it, and the reacter may be uncertain which one he is about to receive.The reaction would then hardly seem to occur without a preliminary recognition and choice.We shall see, however, in the appropriate chapters, that the discrimination and choice involved in such a reaction are widely different from the intellectual operations of which we are ordinarily conscious under those names.Meanwhile the simple reaction-time remains as the starting point of all these superinduced complications.It is the fundamental physiological constant in all time-measurements.As such, its own variations have an interest, and must be briefly passed in review.[122]

The reaction-time varies with the individual and his ageAn individual may have it particularly long in respect of signals of one sense (Buccola, p.147), but not of others.Old and uncultivated people have it long (nearly a second, in an old pauper observed by Exner, Pflüger's Archiv, vii, 612-4).Children have it long (half a second, Herzen in Buccola, p.152).

Practice shortens it to a quantity which is for each individual a minimum beyond which no farther reduction can be made. The aforesaid old pauper's time was, after much practice, reduced to 0.1866 sec. (loc.cit. p. 626).

Fatigue lengthens it.

Concentration of attention shortens it. Details will be given in the chapter on Attention.

The nature of the signal makes it vary.[123] Wundt writes:

"I found that the reaction-time for impressions on the skin with electric stimulus is less than for true touch-sensations, as the following averages show:

	Average.	Average Variation
Sound	0.167 sec.	0.0221 sec.
Light	0.222 sec.	0.0219 sec.
Electric skin-sensation	0.201 sec.	0.0115 sec.
Touch-sensations	0.213 sec.	0.0134 sec.

"I here bring together the averages which have been obtained by some other observers:

	Hirsch.	Hankel.	Exner.
Sound	0.149	0.1505	0.1360
Light	0.200	0.2246	0.1506
Skin-sensation	0.182	0.1546	0.1337"[124]

Thermic reactions have been lately measured by A. Goldscheider and by Vintschgau (1887), who find them slower than reactions from touch. That from heat especially is very slow, more so than from cold, the differences (according to Goldscheider) depending on the nerve-terminations in the skin.

Gustatory reactions were measured by Vintschgau. They differed according to the substances used, running up to half a second as a maximum when identification took place. The mere perception of the presence of the substance on the tongue varied from 0''. 159 to 0''. 219 (Pflüger's Archiv, xiv, 529).

Olfactory reactions have been studied by Vintschgau, Buccola, and Beaunis. They are slow, averaging about half a second (cf. Beaunis, Recherches exp. sur l'Activité Cérébrale, 1884, p. 49 ff.) .

It will be observed that sound is more promptly reacted on than either sight or touch.Taste and smell are slower than either. One individual, who reacted to touch upon the tip of the tongue in 0''. 125, took 0''. 993 to react upon the taste of quinine applied to the same spot. In another, upon the base of the tongue, the reaction to touch being 0''. 141, that to sugar was 0''. 552 (Vintschgau, quoted by Buccola, p. 103). Buccola found the reaction to odors to vary from 0''. 334 to 0''. 681, according to the perfume used and the individual.

The intensity of the signal makes a difference. The intenser the stimulus the shorter the time. Herzen (Grundlinien einer allgem. Psychophysiologie, p. 101) compared the reaction from a corn on the toe with that from the skin of the hand of the same subject. The two places were stimulated simultaneously, and the subject tried to react simultaneously with both hand and foot, but the foot always went quickest. When the sound skin of the foot was touched instead of the corn, it was the hand which always reacted first. Wundt tries to show that when the signal is made barely perceptible, the time is probably the same in all the senses, namely, about 0.332'' (Physiol. Psych. , 2d ed. , ii, 224).

Where the signal is of touch, the place to which it is applied makes a difference in the resultant reaction-time.G.S.Hall and V.Kries found (Archiv f.Anat.u.Physiol., 1879) that when the finger-tip was the place the reaction was shorter than when the middle of the upper arm was used, in spite of the greater length of nerve-trunk to be traversed in the latter case.This discovery invalidates the measurements of the rapidity of transmission of the current in human nerves, for they are all based on the method of comparing reaction-times from places near the root and near the extremity of a limb.The same observers found that signals seen by the periphery of the retina gave longer times than the same signals seen by direct vision.

The season makes a difference, the time being some hundredths of a second shorter on cold winter days (Vintschgau apud Exner, Hermann's Hdbh. , p. 270).

Intoxicants alter the time. Coffee and tea appear to shorten it. Small doses of wine and alcohol first shorten and then lengthen it; but the shortening stage tends to disappear if a large dose be given immediately. This, at least, is the report of two German observers. Dr. J. W. Warren, whose observations are more thorough than any previous ones, could find no very decided effects from ordinary doses (Journal of Physiology, viii, 311). Morphia lengthens the time. Amyl-nitrite lengthens it, but after the inhalation it may fall to less than the normal. Ether and chloroform lengthen it (for authorities, etc., see Buccola, p. 189).

Certain diseased states naturally lengthen the time.

The hypnotic trance has no constant effect, sometimes shortening and sometimes lengthening it (Hall, Mind, viii, 170; James, Proc. Am. Soc. for Psych. Research, 246).

The time taken to inhibit a movement (e.g. to cease contraction of jaw-muscles) seems to be about the same as to produce one (Gad, Archiv f. (Anat. u.) Physiol. , 1887, 468; Orchansky, ibid.1889, 1885).

An immense amount of work has been done on reaction-time, of which I have cited but a small part.It is a sort of work which appeals particularly to patient and exact minds, and they have not failed to profit by the opportunity.

CEREBRAL BLOOD-SUPPLY.

The next point to occupy our attention is the changes of circulation which accompany cerebral activity