Late observations also show, as far as they are sufficient, that the centre for music expression is also located nor- mally in the left hemisphere for right-handed persons. Oppenheim reports a case ^ of total aphasia with total amusia (lack of musical ability from disease) in which the recovery of speech brought with it musical recovery also. Furthermore, another case of Oppenheim's shows motor aphasia with motor amusia only — i.e., the patient could still understand tunes, and, further, could imagine tunes ' in his head,' 2 while he could not sing them. This shows a close connection in locality between motor speech and motor music function, while a slight separateness of the two centres in locality in the left hemisphere explains 2 Cf. Chap. XIV., below, for further exposition of the mechanism of speech and the music function.
Theoretical, 7 1 cases of motor aphasia in which musical execution is pre- served. Further, Frankl-Hochwart declares that no cases are recorded of amusia from lesion in the right hemis- phere/ and Starr says of a patient of his: ^ '' My patient is right-handed, and music does follow speech in being unilaterally located;...it is well proved that the musi- cal faculty is one-sided in location." Despite these posi- tive opinions, however, I think more critical cases with autopsy are necessary to make the position quite secure.
The service which speech owes to gesture is emphasized by Romanes in the following words: " Although gesture language is not in my opinion so efficient a means of developing abstract ideation as is spoken language, it must nevertheless have been of much service in assisting the growth of the latter, and...in laying the foundation of the whole mental fabric which has been constructed by the faculty of speech. Whether we look to children, to savages, or, in a lesser degree, to idiots, we find that ges- ture plays an important part in assisting speech; and in all cases where a vocabulary is scanty or imperfect, ges- ture is sure to be employed as the natural means of supplementing speech...Therefore it is, in my opinion, perfectly certain that its origin and development must have been assisted by gesture. There can be no doubt that the reciprocal influence must have been great in both directions, and that it must have proceeded from gesture to speech in the first instance, and afterwards from speech to gesture."
^ This means that all cases noted have been right-handed. Deutsche Zeitsch. fur Nervenheilkmide, 1891, I., p. 295, and foot-note.
- In a private letter. The case is referred to by Starr in The Psychological Review, January, 1894, p. 92.
72 The Origin of Right-handedness, All this means simply that the general cause to which is due the fact of right-handedness is also the cause, through further differentiation and emphasis in the same local seat, of the development of speech and of musical ability. It now remains to ask: What was or is this cause, and when in the race-history series did it begin to operate? There are only two hypotheses of any force — either that of ' experience,' or that of ' spontaneous varia- tion ' at some stage in biological development.
It is extremely improbable.that dextrality should have arisen among the quadrupeds, or amanous bipeds, for experience was lacking of unilateral stimulation, and a spontaneous variation of this kind would have produced such inconvenience of locomotion and ultimately such asymmetry of form that it would have been weeded out.^ As an extreme example, fancy a bird become dextral in its flight.2 As soon as we come to bipeds with hands, however, these reasons do not hold. Their locomotion does not depend on manual symmetry, and any dextrality, however slight, would be of direct advantage in climbing, fighting, breaking sticks, and pulling fruit; since a disproportionate growth of one side would give that side greater strength than either side would possess in animals of symmetrical development in the same environment. A very strong one-armed man can keep at bay a weaker man with two arms, or destroy him; and this is emphasized in animals, where brute force is the only resource. It is difficult to 1 For this reason the human leg, as Brown-Sequard says, is not as one- sided as the arm. Any great unevenness would produce lameness and relative incapacity.
2 The only evidence I know of such a thing is that a cat swims in a circle; but then dogs and horses do not, and these do not drown, while the cat does.
i Theoretical. 73 find, however, in the habits of simians any ground for beHeving that there has been a form of unilateral stimula- tion which would act to effect a structural change in one hemisphere over and above the other. This, rather than the anatomical causes suggested by Romanes, may be the reason that the animals have not developed speech. Their conditions of life stimulation are such that there has been no chance for the development of the centre for * expression ' in the left temporal brain-lobe. They have been compelled to maintain bilateral balance of function.
But, apart from this, there is every reason to expect, quite independently of function, that two organs of such comparative separateness and independence of function as the two hemispheres would not remain exactly balanced in function; in short, spontaneous variations giving advan- tageous dextrality would inevitably arise and persist as soon as the habits of life were not such that more impor- tant functions, such as locomotion, tended to suppress them and restore bilateral equilibrium.^ There are, as far as I know, very few published observations of fact in regard to simian or animal dextrality.^ 1 It is on this point that I differ from Wilson, who claims that, while some are naturally right- or left-handed, most people owe the peculiarity to educa- tion; the evidence against Wilson's view, apart from my present results, is well put by Mazel, loc. cit.
2 I know only the assertion of Vierordt that parrots grasp and hold food with the left claw, that lions strike with the left paw, and his quotation from Livingstone — ' All animals are left-handed ' (Vierordt, loc. cit., p. 428). Dr. W. Ogle reports observations on parrots and monkeys in Trans. Royal Med. and Chirur. Society, 187 1. Dr. Ogle informs me in a private letter that the chimpanzee which recently died in the Zoological Garden in London was discovered by him to be left-handed. I have addressed a circular letter to some of the officials in zoological institutions here and abroad, and hope to 74 The Origin of Right-handedness, It is likely, therefore, that right-handedness in the child is due to differences in the two half-brains, reached at an early stage in life, that the promise of it is inherited, and that the influences of infancy have little effect upon it. Yet, of course, regular habits of disuse or of the cultiva- tion of the other hand may, as the child grows up, diminish or destroy the disparity between the two. And this inherited brain-onesidedness also accounts for the association of right-handedness, speech, and music faculty, the speech function being a further development of the same unilateral power of movement found first in right- or left-handedness.
II. A further point of psychological interpretation is of some interest. How are we to account for the fact that a bright colour stimulus exposed at a lesser distance brought out the right hand, while a neutral stimulus required a greater distance } The general fact may be expressed in the symbols of the formula which I have proposed for the so-called gather some facts in this way. If it should prove true that the lower animals are left-sided, then the current view that right-handed children have a pre- liminary period of left-handedness — a view to which my Table III., above, gives some support — might have its explanation in the hypothesis of the repe- tition of phylogenetic development in the individual child.
It is evident that on this theory of spontaneous variation any change which produced a permanent organic superiority of one hemisphere \\'Ould be sufficient, and the view that the difference in the hemispheres is due to a better blood supply to the left hemisphere might thus have its justification. As a matter of fact, the arterial arrangements do seem to indicate a more direct blood supply to the left hemisphere (cf. the note of Dr. J. T. O'Connor, apropos of my experiments, in Science, XVI., 1890, p. 331). It is an interest- ing inquiry whether this arterial arrangement is reversed in left-handed per- sons. Wilson cites two cases in which there was no such correspondence Theoretical.
75 dynamogenic method of experimentation. It will be re- membered that in the formula ^ D represented the drawing-out tendency, the amount of dynamogeny exercised by a given stimulus; q the quality of this stimulus (colour, etc.); and d the distance. If the tendency to use one particular hand in preference to the other hand be designated by r, we now find from the experiments that but, by the general law that distance decreases influence.
Again, we find from the experiments that I ^ (colour) but D — iC'q\ consequently, r=K'jy the same result as (3).
So it seems from both results of the experiments that right-handedness varies inversely as the dy?iamogenic inflii- e7ice of the stimuhis, whether that dynamogenic influence be colour or distance.
The question of interpretation, then, is this: How does it come that increasing distance, which would be sup- 76 The Origin of Right-handedness.
posed to lessen the calling-out force of a stimulus by lessening its intensity, clearness, etc., yet tends to do exactly what a bright colour at a lesser distance does, i.e., to call out increased dynamogeny, with the use of the right hand?
Of course the explanation is evident enough. The child has learned by experience, or has inherited an organic experience, that more effort, higher D, is necessary in the case of a more distant stimulus; and so a central supply goes out to reinforce the influence D of this distant stimulus, and the right-handedness is the evidence of this reinforced D. We would expect, on the other hand, that the colour, being itself a more dynamogenic stimu- lus, would have the same effect, without the central rein- forcement, and also bring out the right hand.^ And so it does.
A farther point of interest is seen in the inhibition of the movement altogether when the distance is slightly increased, i.e., to fifteen inches or over, as given in the tables. It shows that even at the age of this child very accurate visual estimation of distance has already been acquired, as I had occasion to say in the last chapter. The child's interpretation of the distance inhibits all effort to reach across it. The interpretations undoubtedly result, in the case of the child, in my opinion, from 1 On this point, Professor William James writes {^Scioice, Nov. 14, 1890, p. 295), apropos oi my experiments when first announced: " These observa- tions seem very interesting, as showing how strong (attractive) stimuli may pro- duce more definitely localized reactions than weaker ones. The baby grasped at bright colours with the right hand almost exclusively." I find this but natural, not because the reaction is * more definitely localized,' but because that is an incident to a larger and more massive discharge through the particu- lar channel which is ready for it.
Theoretical. 77 Theoretical. 77 associations of visual indications of distance with sensa- tions of hand and arm movement. And I find that this association gives rise to three determinations — all matters of experience and all becoming remarkably re- fined— (i) the safe-reacJiiiig distance {\\s(i of either hand or both); (2) the iinccrtain-rcacJiing distance {\\^q. of right hand); and (3) the impossible-to-reacJi distance (no hand movement, but a turning away of face and body).
The process of learning this lesson in distance, and with it the waxing ability of the stronger hand, is so graphically described by James in a private letter that I quote it, with his permission: " Admitting the experience hypothesis (which I adopt from you now,^ since I have made no ob- servations, and your sense of what is likely in this regard seems to me to have great weight), the way I represent the matter to myself is thus: The child originally re- sponds to all optical excitements which strike his atten- 1 In view of my letter in Science, Nov. 28, 1890, p. 302. He adds, how- ever, after the above quotation: " Although I have made every possible con- cession to the experience theory, as adopted by you, I must say that the notion of a specialized native impulsiveness for the right hand when certain distances appeal to the eye lingers in my mind as that of a natural possibility." This is refuted, I think, by the fact that infants at first 'grasp at the moon' with either hand indiscriminately, the ' moon ' standing for any object at any dis- tance. The possibility of such native adaptations cannot be doubted, for some young animals seem to have different native responses adjusted to different distances; but in the case of the child, experience seems to be waited for to develop many things which are really native.
I endeavoured to test H.'s native sense of locality on the body, apart from the association with sight, by dangling my watch-chain gently from day to day on the top of her head, and by gently pinching one or other of her ears occasionally, watching the movements of her hands in their search for the chain and the ear. Up to about the middle of her third month the hand movements seemed perfectly random, ' up ' and ' back ' being about the only tendencies which indicated any sense of locality whatever. In the third month, however, she seemed to begin to learn where to find the objects, especially the ear; but the success was apparently due to the experience.
78 The Origin of Right-handedness.
tion by bounding up and down, and moving both arms. Ere long the movement becomes one of grasping with both. Some graspings prove easy, and the original bi- lateral medianism continues for a while associated with these. Others are protracted; and the superior native efficiency of the right hand, in reaching the goal, here acts so as to inhibit the left hand altogether when the stimulus suggests a case of this kind. Others, again, never succeed, the object being beyond range altogether; and all movements are inhibited for these at last."
Now, the point to be observed is this, that the dynamo- genie effect of distance {d in the formula) is not natively provided for, as is that of quality (^, colour in this case): it is an acquired effect, called out through experiences of relative distance. Relative distances are * interpreted ' in terms of past experience, and this gives them their pres- ent force. The course of the nervous disturbance is through the higher circuit which association involves, and which on the motor side implicates attention; while the dynamogenic effect of colour or of sensation qualities generally, which prompt native reactions, is by a lower reflex circuit. One is an ideo-motor reaction, based on association; the other is a native sensori-motor reaction.
It is necessary, therefore, again to alter profoundly our conception of the simplest dynamogenic formula in view of the element of association in the simplest reaction in- volving distance. And it is easy to see what becomes of the formula as soon as association gets to be a little com- plex: for d, we must substitute a symbol to stand for the central influence as a whole, say <^; and of course with increasing complexity of experience the meaning of ^ becomes more and more recondite. With adults, there- Theoretical. 79 Theoretical. 79 fore, such a formula would be in most cases nothing more than tautology.^ With infants it remains useful only for 1 The only way to experiment on volition, accordingly, is by using com- parative stimulations of no meaning or association, or by keeping the associa- tion element constant, by using the same stimulation repeatedly. I have endeavoured to experiment on volition by observing the effect on action of the same stimulation apprehended through different senses, i.e.^ the tendency to draw a figure seen in one case and traced by the hand in the other {^Proc. Cong. Exper. Psych., London, 1892, p. 51); see also below. Chap. XIII., § 3.
A further point deserves a word. In the original announcement of these experiments I found it necessary to think that the child's reaching with the right hand only in cases involving long distances and effort could not be ex- plained without supposing that her sense of motor discharge in the case of effort was something different from that in case of movements without effort, i.e., that there was a central sense of motor potential of some kind. Profes- sor James in Science and in private letters, and Professor Dewey later in a private letter, suggest that the child might be guided by its sense of greater success, skill, ease, etc., in the case of earlier right-hand movements — all peripheral, not central, elements. I am not strenuous for my interpretation; indeed the other seems to me now more natural and simple. It is to be hoped that more experiments will be forthcoming; but with my experience with both my children I find certain facts which I cannot explain on the peripheral view: (i) The child does wc?/ show differences of ease, skill, etc., in favour of either hand at this early age, as far as can be detected; (2) after beginning to use the right hand for strenuous efforts the two hands are still used indiscriminately for easy movements, near distances, etc. How can this be explained? Why should not the child economize — as adults do — in all movements, using the right hand after experience of its 'greater efficiency' for everything, when circumstances permit? The view of Professor James seems to require what I may call a * cat and kitten ' arrangement of nervous discharges, i.e., certain l^athways of voluminous discharge for right-hand movements opened up by earlier more successful movements, and, at the same time, other pathwaysyjjr the same discharges \i\\^Xi\t%'S> voluminous — not due to the earlier successful movements. We have not knowledge enough to say it may not be; but it looks to me like a Marge hole for the cat and a little hole for the kitten' — an arrangement which Professor James argues against, at least in one con- nection {Princ. of Psychology, Vol. I., p. 592). But that the child does ex- tend the use of the right hand, even when circumstances would seem to discourage it, is seen in, (3), the very striking fact, that the right hand is used to grasp objects, etc., which lie on the left side of the child; movements in which the left hand would seem to have actually more skill, ease, and practice. Professor Ladd seems to accept my first interpretation (^Psychology, Descriptive and Explanatory, p. 222).
8o The Origin of Right-handedness.
such elementary experiences as those I have enumerated above.
Again, as at the end of the last chapter, I must call attention not only to the complication which these experi- ments give to the method of studying children, but also to the fine uniformity which appears through them in the working of the law of dynamogenesis, upon which rests the theory of development stated in the following chapters.
CHAPTER V.
Infants' Movements. § I. Descriptive; Tracery Imitation.
In earlier chapters, the general conditions of infant's responses in mov^ement have been pointed out and some special problems set: a few points of interest may now be further brought up in connection with the rise of the more complex movements.
From the beginning of independent life, movement is the infant's natural response to all influences. And, more than this. Bain and Preyer seem to have made out their case, that from the outset there are movements which are spontaneous, due to discharge of the motor centres unso- licited by definite external stimulations. At any rate, no observation made after birth can decide the question one way or the other whether sensation or movement is the earlier fact in ontogenetic development. It remains for the embryologists to continue their work, and this is where Preyer's results get their principal value.
Reflexes. — In regard to movements more properly reflex and responsive, I may record a few detached observations on my child. Carefully planned experiments with her, made in the ninth month, showed the native walking reflex — alternative movement of the legs — very strongly G 8x 82 Infants Movements.
marked. I held her by the body, having made the legs quite free, in a position which allowed the bare feet to rest lightly upon a smooth table. The reflex seemed to come somewhat suddenly, for up to the middle of the eighth month I could not discover more than a single alternation; and this I had determined not to take as evi- dence, since it might well arise by chance. But, in the ninth month, I observed as many as three and four well- regulated alternations, in succession. At first most of these movements were the reverse of the natural walking movements, being oftenest such as would carry the child backward. This, however, passed away. I have the fol- lowing note on June 13, 1890, the child being one day short of nine months old: " Walking movements, 3 to 4 alternations, backwards oftenest, but tending rapidly to forward movements; later, 2 experiments, each showing 3 to 4 alternations forwards very plainly;" and on June 19: *' Fine activity in walking reflex — good alternations, but more backwards than forwards — clearly reflex, from stim- ulus to the soles." It is easy to see that this backward alternation ^ might be due to some accident of stimulation or discharge when the reflex was first called out; a tendency which early efforts at creeping would soon correct. Yet in H.'s case, it was so marked that for a period she preferred to creep backward. ^ A few observations. were made also upon unilateral 1 Two other cases of this have been verbally reported to me; but I am not sure of the conditions under which one of them was observed. The second exact observation I owe to Professor Cattell.
2 For interesting experiments on the method and variations of walking by different children of both sexes and by adults, see H. Vierordt, Der Gang des Me7ischen (Tubingen, 1881). Similar valuable observations might be made by measurements of the intervals, directions, etc., of children's footprints in the damp yielding sand of the seashore.
Descriptive. ^t^ reflexes.^ A gentle touch with linger or feather on the cheek, or beside the nose, or upon the ear, when H. was sleeping quietly upon her back, called out always the hand on the same side. After two or three such irritations, her sleep became troubled and she turned upon the bed, or used both hands to rub the place stimulated. Tickling of the sole of the foot also, besides causing a reaction in the same foot, tended to bring about a movement of the hand on the same side. These observations, not a large number, were made in the sixth, seventh, and eighth months.
In order to test the growth of voluntary control over the muscles of the hand and fingers, I determined to observe the phenomena of H.'s attempts at drawing and writing, for which she showed great fondness as soon as imitation was well fixed. Selecting a few objects well differentiated in outline, — animals which she had already learned to recognize and name after a fashion, — I drew them one by one on paper and let her imitate the ^copy.' The results I have in a series of ' drawings ' of hers, ex- tending from the last week of her nineteenth month to the middle of the twenty-seventh month. The results show that, with this child, up to the beginning of the twenty-seventh month there was no connection apparent between a mental picture in consciousness and the move- ments made by the hands and fingers in attempting to draw it. The ' drawing ' was simply the vaguest and most general imitation of the teacher's movements, not the tracing of a mental picture. And the attempt was no better when a 'copy ' was made by myself on the paper — 1 Cf. Kussmaul, Untersuchungen zur Seelenlehcji der Neiigebornen Afcnsche7i^ p. 1 8, for similar experiments; and Vierordt, in Gerhardes Ilandbuch der Kinder krankheilen^ I., p. 215.
84 Infants Move merits.
a rough outline drawing of a man, etc. There was no semblance of conformity between the child's drawing and the copy. Further, while she could identify the copy and name the animal, she could not identify her own effort, except so far as she remembered what object she set out to make. See Figures I., II., III., and IV., for speci- mens illustrating the straightness and rigidity of her early attempts.
Man: 19th month.
Cat: 10th month. Man: 20th month.
Fig. I. — Early Drawings with Copy.
Man: 20th month. Bird: 20th month.
Fig. II. — Early Drawings without Copy.
With it all there was on her face an expression of dis- satisfaction with her later attempts, similar to that which one observes in the efforts of the year-old to speak. My little girl would hide her head after making a drawing, extend the pencil to me, and say, 'Papa make man.' It seemed to indicate a sense of what was expected beyond the ability to attain the process of accomplishing it.
Tracery Iviiiation, Tracery Iviiiation, In Figs. III. and IV. we see some growth in variety of shape and direction with increased mobiUty of the hand and arm, but still no imitation in outline is apparent.
c Horse.
b. Cat. d. Cow.
Fig. III. — Drawings without Copy: End of 25TH Month.
a. Man (two trials)- b- Bird.
Fig. IV. — With Copy: Early in 26TH Month.
Fig. V. shows further complications in movement.
a, Man: with copy. b. Man: without copy.
Fig. v. — Later more Complicated Drawings.
86 Infants Movements.
In the nature of the movements which the child made in this series of drawings, there is marked change and development which may be briefly described. There is growth from angular straight lines to curves, from move- ments one way exclusively to reverse movements, and an increasing tendency to complex intricate figures, which last probably results from greatly increased ease, variety, and rapidity of movement. At first she made only sweep- ing ' arm movements,' then began to flex the wrist some- what, and toward the end of the series given above, as is evident in the figures, with no teaching, manipulated the pencil with her fingers considerably. This seems to give support to the opinion of professional writing-teachers that the * arm movement ' is most natural and effective for purposes of penmanship.