The Principles of Psychology, Vols. 1-2

one keeps one's mind as intent as possible upon the ex pected signal, and ' purposely avoids ' * thinking of the move ment to be executed ; in the t extreme muscular ' way one 1 does not think at all ' t of the signal, but stands as ready as possible for the movement. The muscular reactions are much shorter than the sensorial ones, the average differ ence being in the neighborhood of a tenth of a second. Wuudt 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 Wundtia.n 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 reactor has succeeded by repeated and conscientious practice in bringing about an extremely precise co-ordina tion of his voluntary impulse with his sense-impression do we get times which can be regarded as typical sensorial reaction-times/' J 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 percep tion 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 pre pared by straining one's attention towards the movement. § 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 phe nomenon 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 § Lange has an interesting hypothesis as to the brain-process concerned in the latter, for which I can only refer to his essaymethod,' giving both the shortest times and the most con stant ones, ought to be aimed at in all comparative investi gations. Herr Lange's own muscular time averaged (T.123 ; his sensorial time, 0".230.

These reaction-time experiments are then in no sense measurements of the swiftness of thought. Only 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 pre liminary 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 con scious under those names. Meanwhile the simple reactiontime remains as the starting point of all these superinduced complications. It is the fundamental physiological con stant in ail time-measurements. As such, its own variations have an interest, and must be briefly passed in review.*

The reaction-time varies with the individual and his age. An 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, Pfliiger'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 indi vidual 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).

* The reader who wishes to know more about the matter will find a most faithful compilation of all that has been done, together with much original matter, in G. Buccola's 'Legge del Tempo,' etc. See also chap ter xvi of Wundt's Physiol. Psychology; Exner in Hermann's Hdbch., Bd. 2, Thl. ii. pp. 252-280; aJso Ribot's Contemp. Germ. Psych chap. vm. Concentration of attention shortens it. Details will be given in the chapter on Attention. u 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:

"I here bring together the averages which have been obtained by some other observers : Thermic reactions have been lately measured by A. Goldscheider and by Vintschgau (1887), who find them slower than reactions from touch. That from heat espe cially is very slow, more so than from cold, the differences (according to Goldscheider) depending on the nerve-ter minations 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 (Pfliiger's Archiv, xiv. 529).

*The nature of the movement also seems to make it vary. Mr. B. I. Oilman and I reacted to the same signal by simply raising our hand, and again by carrying our hand towards oiir back. The moment registered was always that at which the hand broke an electric contact in starting to move. But it started one or two hundredths of a second later when the more extensive movement was the one to be made. Orchansky, on the other hand, experimenting on contractions of the masseter muscle, found (Archiv f. (Anat. u.) Physiol., 1889, p. 187) that the greater the amplitude of contraction intended, the shorter grew the time of reaction. He explains this by the fact that a more ample contraction makes a greater appeal to the attention, and that this shortens the times.

Buccola, and Beaunis. They are slow, averaging about half a second (cf. Beaunis, Recherches exp. sur 1'Activite Cerebrale, 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 Ox/.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., n. 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.

dredths of a second shorter on cold winter days (Vintschgau apud Exner, Hermann's Hdbli., p. 270). Intoxicants alter the time. Coffee and tea appear to shorten it. Small doses of ivine and alcohol first shorten and then lengthen it ; but the shortening stage tends to disap pear 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, vm. 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).

The hypnotic trance has no constant effect, sometimes shortening and sometimes lengthening it (Hall, Mind, vm. 170 ; James, Proc. Am. Soc. for Psych. Kesearch, 246). An immense amount of work has been done on reactiontime, 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. The next point to occupy our attention is the changes of circulation which accompany cerebral activity.

All parts of the cortex, when electrically excited, produce alterations both of respiration and circulation. The bloodpressure rises, as a rule, all over the body, no matter where the cortical irritation is applied, though the motor zone is the most sensitive region for the purpose. Elsewhere the current must be strong enough for an epileptic attack to be produced.* Slowing and quickening of the heart are also observed, and are independent of the vaso-constrictive phenomenon. Mosso, using his ingenious 'plethysmo-

graph' as an indicator, discovered that the blood-supply to the arms diminished during intellectual activity, and found furthermore that the arterial tension (as shown by the sphygmograph) was increased in these members (see FIG. 23.— Sphymographic pulse-tracing. A, during intellectual repose ; B, during in tellectual activity. (Mosso.) Fig. 23). So slight an emotion as that produced by the entrance of Professor Ludwig into the laboratory was in stantly followed by a shrinkage of the arms.* The brain itself is an excessively vascular organ, a sponge full of blood, in fact ; and another of Mosso's inventions showed that when less blood went to the arms, more went to the head. The subject to be observed lay on a delicately bal anced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in conse quence of the redistribution of blood in his system. But the best proof of the immediate afflux of blood to the brain during mental activity is due to Mosso's observations on three persons whose brain had been laid bare by lesion of the skull. By means of apparatus described in his book, f this physiologist was enabled to let the brain-pulse record itself diroctly by a tracing. The intra-cranial blood-pressure rose immediately whenever the subject was spoken to, or when he began to think actively, as in solving a problem in mental arithmetic. Mosso gives in his work a large num ber of reproductions of tracings which show the instantaneity of the change of blood-supply, whenever the mental activity was quickened by any cause whatever, intellectual

t Ueber den Kreislauf des Blutes im menschlicheii Gehirn (1881). chap. ii. The Introduction gives the history of our previous knowledge :>f the subject. or emotional. He relates of his female subject that one day whilst tracing her brain-pulse he observed a sudden rise with no apparent outer or inner cause. She however confessed to him afterwards that at that moment she had caught sight of a skull on top of a piece of furniture in the voom3 and that this had given her a slight emotion.

The fluctuations of the blood supply to the brain were independent of respiratory changes,* and followed the quickening of mental activity almost immediately. We must suppose a very delicate adjustment whereby the cir culation follows the needs of the cerebral activity. Blood very likely may rush to each region of the cortex accord ing as it is most active, but of this we know nothing. I need hardly say that the activity of the nervous matter is the primary phenomenon, and the afflux of blood its secondary consequence. Many popular writers talk as if it were the other way about, and as if mental activity were due to the afflux of blood. But, as Professor H. N. Martin has well said, "that belief has no physiological foundation whatever; it is even directly opposed to all that we know of cell life."f A chronic pathological congestion may, it is true, have secondary consequences, but the primary congestions which we have been considering follow the activity of the brain-cells by an adaptive reflex vaso-motor mechanism doubtless as elaborate as that which harmonizes bloodsupply with cell-action in any muscle or gland.

Of the changes in the cerebral circulation during sleep I will speak in the chapter which treats of that subject. Brain-activity seems accompanied by a local disengagement of heat. The earliest careful work in this direction was by Dr. J. S. Lombard in 1867. Dr. Lombard's latest results in clude the records of over 60,000 observations.^: He noted the * In this conclusion M. Gley (Archives de Pbysiologie, 1881, p. 742) agrees with Professor Mosso. Gley found his pulse rise 1-3 beats, his carotid dilate, and his radial artery contract during hard mental work. f Address before Med. and Chirurg. Society of Maryland, 1879 ^ See his book. "Experimental Researches on the Regional Tempera lure of the Head" (London. 1879).

changes in delicate thermometers and electric piles placed against the scalp in human beings, and found that any intel lectual effort, such as computing, composing, reciting poetry silently or aloud, and especially that emotional excitement such as an anger fit, caused a general rise of temperature, which rarely exceeded a degree Fahrenheit. The rise was in most cases more marked in the middle region of the head than elsewhere. Strange to say, it was greater in reciting poetry silently than in reciting it aloud. Dr. Lombard's explanation is that " in internal recitation an additional portion of energy, which in recitation aloud was con verted into nervous and muscular force, now appears as heat." * I should suggest rather, if we must have a theory, that the surplus of heat in recitation to one's self is due to inhibitory processes which are absent when we recite aloud. In the chapter on the Will we shall see that the simple cen tral process is to speak when we think ; to think silently involves a check in addition. In 1870 the indefatigable Schiff took up the subject, experimenting on live dogs and chickens, plunging thermo-electric needles into the sub stance of their brain, to eliminate possible errors from vascular changes in the skin when the thermometers were placed upon the scalp. After habituation was established, he tested the animals with various sensations, tactile, optic, olfactory, and auditory. He found very regularly an im mediate deflection of the galvanometer, indicating an abrupt alteration of the intra-cerebral temperature. When, for in stance, he presented an empty roll of paper to the nose of his dog as it lay motionless, there was a small deflection, but when a piece of meat was in the paper the deflection was much greater.

Schiff concluded from these and other experiments that sensorial activity heats the brain-tissue, but he did not try to localize the increment of heat beyond finding that it was in both hemispheres, whatever might be the sensation applied, t Dr. E. W. Amidon in 1880 made a farther step forward, in localizing the heat produced by voluntary muscular contractions. Applying a number of f The most convenient account of Schiff's experiments is by Prof, fierzen, in the Revue Philosophique, vol. in. p. 36.

delicate surface-thermometers simultaneously against the scalp, he found that when different muscles of the body were made to contract vigorously for ten minutes or more, different regions of the scalp rose in temperature, that the regions were well focalized, and that the rise of temperature was often considerably over a Fahrenheit degree. As a re sult of his investigations he gives a diagram in which num bered regions represent the centres of highest temperature for the various special movements which were investigated. To a large extent they correspond to the centres for the same movements assigned by Ferrier and others on other grounds ; only they cover more of the skull.*

Chemical action must of course accompany brain-activity. But little definite is known of its exact nature. Cholesterin and creatin are both excrementitious products, and are both found in the brain. The subject belongs to chemistry rather than to psychology, and I only mention it here for the sake of saying a word about a wide-spread popu lar error about brain-activity and phosphorus. ' Ohm Phosphor, kein Gedanke,' was a noted war-cry of the ' materialists ' during the excitement on that subject which filled Germany in the '60s. The brain, like every other organ of the body, contains phosphorus, and a score of other chemicals besides. Why the phosphorus should be picked out as its essence, no one knows. It would be equally true to say ' Ohne Wasser kein Gedanke,' or ' Ohne Kochsalz kein Gedanke ' ; for thought would stop as quickly if the brain should dry up or lose its NaCl as if it lost its phosphorus. In America the phosphorus-delusion has twined itself round a saying quoted (rightly or wrongly) from Professor L. Agassiz, to the effect that fishermen are more intelligent than farmers because they eat so much fish, which contains so much phosphorus. All the facts may be doubted.

phosphorus to thought would be to find whether more is excreted by the brain during mental activity than during rest. Unfortunately we cannot do this directly, but can only gauge the amount of PO6 in the urine, which repre sents other organs as well as the brain, and this procedure, as Dr. Edes says, is like measuring the rise of water at the mouth of the Mississippi to tell where there has been a thunder-storm in Minnesota.* It has been adopted, how ever, by a variety of observers, some of whom found the phosphates in the urine diminished, whilst others found them increased, by intellectual work. On the whole, it is impossible to trace any constant relation. In maniacal excitement less phosphorus than usual seems to be excreted. More is excreted during sleep. There are differences be tween the alkaline and earthy phosphates into which I will not enter, as my only aim is to show that the popular way of looking at the matter has no exact foundation, f The fact that phosphorus-preparations may do good in nervous exhaustion proves nothing as to the part played by phos phorus in mental activity. Like iron, arsenic, and other remedies it is a stimulant or tonic, of whose intimate work ings in the system we know absolutely nothing, and which moreover does good in an extremely small number of the cases in which it is prescribed.

The phosphorus-philosophers have often compared thought to a secretion. " The brain secretes thought, as the kidneys secrete urine, or as the liver secretes bile," are phrases which one sometimes hears. The lame analogy need hardly be pointed out. The materials which the brain pours into the blood (cholesterin, creatin, xanthin, or what ever they may be) are the analogues of the urine and the bile, being in fact real material excreta. As far as these matters go, the brain is a ductless gland. But we know of nothing connected with liver- and kidney-activity which can

f Without multiplying references, I will simply cite Mendel (Archiv f . Psychiatric, vol. in, 1871), Mairet (Archives de Neurologic, vol. ix, 1885), and Beaunis (Rech. Experimentales sur 1'Activite Cerebrale, 1887). Richet gives a partial bibliography in the Revue Scientifique, vol. 38, p. 788 (1886). be in the remotest degree compared with the stream of thought that accompanies the brain's material secretions. There remains another feature of general brain-physi ology, and indeed for psychological purposes the most important feature of all. I refer to the aptitude of the brain for acquiring habits. But I will treat of that in a chapter by itself.

WHEN we look at living creatures from an outward point of view, one of the first things that strike us is that they are bundles of habits. In wild animals, the usual round of daily behavior seems a necessity implanted at birth; in animals domesticated, and especially in man, it seems, to a great extent, to be the result of education. The habits to which there is an innate tendency are called instincts ; some of those due to education would by most persons be called acts of reason. It thus appears that habit covers a very large part of life, and that one engaged in studying the objective manifestations of mind is bound at the very out set to define clearly just what its limits are.

The moment one tries to define what habit is, one is led to the fundamental properties of matter. The laws of Nature are nothing but the immutable habits which the different elementary sorts of matter follow in their actions and reactions upon each other. In the organic world, how ever, the habits are more variable than this. Even instincts vary from one individual to another of a kind; and are modified in the same individual, as we shall later see, to suit the exigencies of the case. The habits of an elemen tary particle of matter cannot change (on the principles of the atomistic philosophy), because the particle is itself an unchangeable thing ; but those of a compound mass of matter can change, because they are in the last instance due to the structure of the compound, and either outward forces or inward tensions can, from one hour to another, turn that structure into something different from what it was. That is, they can do so if the body be plastic enough to maintain

* This chapter has already appeared in the Popular Science Monthly for February 1887. its integrity, and be not disrupted when its structure yields. The change of structure here spoken of need not involve the outward shape ; it may be invisible and molecular, as when a bar of iron becomes magnetic or crystalline through the action of certain outward causes, or India-rubber becomes friable, or plaster ' sets.' All these changes are rather slow ; the material in question opposes a certain resistance to the modifying cause, which it takes time to overcome, but the gradual yielding whereof often saves the material from being disintegrated altogether. When the structure has yielded, the same inertia becomes a condition of its comparative permanence in the new form, and of the new habits the body then manifests. Plasticity, then, in the wide sense of the word, means the possession of a struc ture weak enough to yield to an influence, but strong enough not to yield all at once. Each relatively stable phase of equilibrium in such a structure is marked by what we may call a new set of habits. Organic matter, especially nervous tissue, seems endowed with a very ex traordinary degree of plasticity of this sort; so that we may without hesitation lay down as our first proposition the following, that the phenomena of habit in living beings are due to the plasticity* of the organic materials of wliich their bodies are composed.

But the philosophy of habit is thus, in the first instance, a chapter in physics rather than in physiology or psychol ogy. That it is at bottom a physical principle is admitted by all good recent writers on the subject. They call atten tion to analogues of acquired habits exhibited by dead mat ter. Thus, M. Leon Dumont, whose essay on habit is per haps the most philosophical account yet published, writes : " Every one knows how a garment, after having been worn a certain time, clings to the shape of the body better than when it was new; there has been a change in the tissue, and this change is a new habit of cohesion. A lock works better after being used some time; at the out set more force was required to overcome certain roughnesses in the mechanism. The overcoming of their resistance is a phenomenon of habituation. It costs less trouble to fold a paper when it has been

* In the sense above explained, which applies to inner structure as well as to outer form. folded already. This saving of trouble is due to the essential nature ot habit, which brings it about that, to reproduce the effect, a less amount of the outward cause is required. The sounds of a violin improve by use in the hands of an able artist, because the fibres of the wood at last contract habits of vibration conformed to harmonic relations. This is what gives such inestimable value to instruments that have belonged to great masters. Water, in flowing, hollows out for itself a channel, which grows broader and deeper; and, after having ceased to flow, it resumes, when it flows again, the path traced by itself before. Just so, the im pressions of outer objects fashion for themselves in the nervous system more and more appropriate paths, and these vital phenomena recur under similar excitements from without, when they have been inter rupted a certain time." *

Not in the nervous system alone. A scar anywhere is a locus minoris resistentice, more liable to be abraded, inflamed, to suffer pain and cold, than are the neighboring parts. A sprained ankle, a dislocated arm, are in danger of being sprained or dislocated again ; joints that have once been attacked by rheumatism or gout, mucous membranes that have been the seat of catarrh, are with each fresh re currence more prone to a relapse, until often the morbid state chronically substitutes itself for the sound one. And if we ascend to the nervous system, we find how many socalled functional diseases seem to keep themselves going simply because they happen to have once begun; and how the forcible cutting short by medicine of a few attacks is often sufficient to enable the physiological forces to get pos session of the field again, and to bring the organs back to functions of health. Epilepsies, neuralgias, convulsive affec tions of various sorts, insomnias, are so many cases in point. And, to take what are more obviously habits, the success with which a 'weaning' treatment can often be applied to the victims of unhealthy indulgence of passion, or of mere complaining or irascible disposition, shows us how much the morbid manifestations themselves were due to the mere inertia of the nervous organs, when once launched on a false career.