will be remembered that the child does not begin to reach for anything that it sees until the fourth or sixth week; so it is evident at what a remarkably fast rate this associa- tion between those obscure factors of size, perspective, light and shade, etc., which signify distance to the eye, becomes associated with arm-movements, in such a way that the inhibition of movement by sensations from the other sense is secured so early.
^ See also the remarks in Chap. IV., § 2. ^ gee below, Chap. VI., § 3.
Critical. 55 In regard to the relative use of the two hands in these and other experiments, — this is a topic to which I may devote the next brief chapter.
§ 2. Critical.
It is in place to recall the criticisms already offered ^ upon the colour experiments of Preyer and Binet. I think the method thus applied successfully obviates all these difficulties of earlier methods. There are certain other requirements of proper procedure, however, which, as far as I am aware, have never been duly weighed by any one who has experimented with young children.
In the first place, fatigue is a matter of considerable importance, not only on this method but on any other. Again, the child is peculiarly susceptible to the appeals of change, novelty, chance, or happy suggestion; and often the failure to respond to a stimulus is due to distraction or to discomfort rather than to lack of intrinsic interesting quality. In respect to fatigue, I would say that the first signs of restlessness, or arbitrary loss of interest, in a series of stimulations, is sufficient warning, and all attempts at further experimenting should cease. Often the child is in a state of indisposition, of trifling nervous irritability, etc.; this should be detected beforehand and then nothing should be undertaken. No series longer than three trials should be attempted without changing the child's position, resting its attention with a song, or a game, etc., and thus leading it fresh to its 'task' again. Further, no single stimulus, as a colour, should be twice repeated without a change to some other: since the child's eagerness or alert- 1 Above, Chap. II., § i.
56 Distajzce and Colour Perception of Infants.
ness is somewhat satisfied by the first effort and a new thing is necessary to bring him out to full exercise again. Further, after each effort or two the child should be given the object reached for to hold or play with for a moment; otherwise he grows to apprehend that the whole affair is a case of Tantalus. In all these matters, very much de- pends upon the knowledge and care of the experimenter, and his ability to keep the child in a normal condition of pleasurable muscular exercise throughout.^ Coming to colour experiments, several requirements would appear to be necessary for exact results. Should not the colours chosen be equal in purity, intensity, lustre, illumination, etc. } In reference to these qualitative dif- ferences,— those which are really important in order to keep our symbol constant as respects all but the qualita- tive colour influence, — I think only that degree of care need be exercised which good comparative judgment pro- vides. Colours of about equal objective intensity, of no gloss, of relatively evident spectral purity, under constant illumination, — this is all that is required: for the variations due to the grosser influences I have mentioned, such as condition of attention, physical unrest, disturbing noises, sights, etc., are of greater influence than any of these more recondite objective variations in the stimulus. Intensity and lustre, however, are certainly important. It is possible, by carefully choosing a room of pretty constant daylight illumination, and setting the experiments at the same hour each day, to secure a regular degree of brightness if the colours themselves are equally bright: and lustre may be 1 It is on account of my extreme care in these points that the number of experiments recorded in the tables in this chapter is so small: as it was, they extended over a period of more than six months. I was then obliged to sep- arate myself from the child, and so the series came to an end.
Critical, 5 7 ruled out by using coloured wools or blotting-papers. The papers used by myself were coloured blotting-papers, which I selected by their empirical properties as good for the purpose. The omission of yellow is due to the absence, in my neighbourhood, of a yellow paper that satisfied me. I did not care to introduce another element of uncertainty in the way of change of texture or general character as to shape, form, etc., as an altogether different object would have done.
The only valid criticism, therefore, on the tables is that which exposes the small number of experiments; and an examination of the table proves it well taken. It has been suggested to me by a friend^ that the results at 11, 12, 13, and 14 inches might be taken together for each colour; since the element of distance would not give important variations within these limits. This, it will be seen, how- ever, on calculation, does not alter the order of colour preference, except to lay more emphasis on white.
On the whole, therefore, I attach some little importance to the experiments apart from their illustrative value and their possible stimulating effect upon others who may care to extend them. For these latter reasons, however, as much as for the positive inferences I have drawn from them above, I have felt that they ought not to be unrecorded. Their main purpose in the progress and plan of this book is seen in their witness to the regularity of operation of the principle of suggestion or dynamogenesis.
1 Mrs. C. Ladd Franklin, who wrote to me kindly about the papers as origi- nally published in Science.
CHAPTER IV.
The Origin of Right-handedness. § I. ExpermiejitaL The question * Why are we right- or left-handed } ' has exercised the speculative ingenuity of many men. It has come to the front anew in recent years, in view of the advances made in the general physiology of the nervous system; and certainly we are now in a better position to set the problem intelligently and to hope for its solution. Hitherto the actual conditions of the rise of 'dextrality' in young children — as the general fact of uneven-handedness may be called — have not been closely observed. It was to gain light, therefore, upon the facts themselves that the experiments described in the following pages were carried out.
My child H. was placed in a comfortable sitting posture, the arms left bare and free in their movement, and allowed to reach for objects placed before her in positions exactly determined and recorded by the simple arrangement of slid- ing rods already described. The experiments took place at the same hour daily, for a period extending from her fourth to her tenth month. These experiments were planned with very great care and with especial view to the testing of several hypotheses which, although superficial to those who have studied physiology, yet constantly recur in publications on 58 Expert Die) I la l. 59 this subject.^ Among these theories certain may be men- tioned with regard to which my experiments were con- clusive. It has frequently been held that a child's right- handedness arises from the nurse's or mother's constant method of carrying it; the child's hand which is left free being more exercised, and so becoming stronger. This theory is ambiguous as regards both mother and child. The mother, if right-handed, would carry the child on the left arm, in order to work with the right arm. This I find an invariable tendency with myself and with nurses and mothers whom I have observed. But this would leave the child's left arm free, and so a right-handed mother would be found with a left-handed child. Again, if the mother or nurse be left-handed, the child would tend to be right- handed. Or if, as is the case in civilized countries, nurses largely replace the mothers, it would be necessary that most of the nurses be left-handed in order to make most of the children right-handed. Now none of these deductions are true. Further, the child, as a matter of fact, holds on with both hands, however it is itself held.
Another theory maintains that the development of right- handedness is due to differences in weight of the two lateral halves of the body; this tends to bring more strain on one side than the other, and so to give more exercise, and so more development, to that side. This evidently assumes that children are not right- or left-handed before they learn to stand. This my results given below show to be false. Again, we are told that infants get right-handed by being placed on one side too much for sleep; this can 1 Cf. Vierordt's remarks, Physiologie des Kindesalters, pp. 428, 429. For a detailed statement of theories on this topic, see Chap. X. of the very learned monograph on The Right Hand: Left-handedness, by my late lamented col- league and friend Sir Daniel Wilson.
6o The Origin of Right-handedness, be shown to have little force also, when the precaution is taken to place the child alternately on its right and left sides for its sleeping periods.
In the case of the child H., certain precautions were carefully enforced. She was never carried about in arms at all, never walked with when crying or sleepless (a ruinous and needless habit to cultivate in an infant); she was frequently turned over in her sleep; she was not allowed to balance herself on her feet until a later period than that covered by the experiments. Thus the condi- tions of the rise of the right-handed era were made as simple and uniform as possible.
The experiments included, besides reaching for colours, a great many of reaching for other objects, at longer and shorter distances, and in unsymmetrical directions. The following table (III.) gives some details of the results of the experiments in which simple objects were used, extending over a period of four months, from the fifth to the ninth in her life. The number of experiments at each sitting varied from ten to forty; the position of the child being reversed, as to light from windows, position of observation, etc., after half of each series.
TABLE III.
Date.
No. of Series.
No. of Ex- periments.
Right Hand.
Left Hand.
Both Hands.
1890. February lOth to March 15th March 14th to April 14th.. April 14th to May 14th...30 25 25 16 57 86 Total 96 Expcrimaital.
6i It is evident from Table III. that no trace of preference for either hand is discernible during this period; indeed, the neutrality is as complete as if it had been arranged beforehand, or had followed the throwing of dice.
I then conceived the idea that possibly a severer dis- tance test might affect the result and show a marked preferential response by one hand over the other. I accordingly continued to use a neutral stimulus, but placed it from 12 to 15 inches away from the child. This resulted in very hard straining on her part, with all the signs of physical effort (explosive breathing-sounds result- ing from the setting of the larynx, rush of blood to the head, seen in flushing of the face, etc., and flow of urine). Table IV. gives the results; the number in each series was intentionally made very small, from one to twelve, in order to avoid fatigue.
TABLE IV.
Date.
No. of Series.
No. of Trials.
Right Hand.
Left Hand.
Both Hands.
1890. May 26th to June lOth 32 80 74 5 I The same cases, distributed according to distance, give us Table V.
TABLE V.
12 Inches.
13 Inches.
14 Inches.
15 Inches.
A comparison of Tables IV. and V. with Table III. shows a remarkable difference. During the month ending June 15th, the child showed no decided preference for either hand in reaching straight before her within the easy reach- ing distance of 10 inches, but a slight balance in favour of the left hand; yet she was right-handed to a marked degree during the same period as regards movements which required effort or strain, such as grasping for ob- jects 12 to 15 inches distant. For the greater distances, the left hand was used in only five cases as against sev- enty-four cases of the use of the right hand; and further, all these five cases were twelve-inch distances, the left hand being used absolutely not at all in the forty-five cases at longer distances.
In order to test this further, I varied the point of ex- posure of the stimulus to the right or left, aiming thus to attract the hand on one side or the other, and so to deter- mine whether the growth or such a preference was limited to experiences of convenience in reaching to adjacent local objects, etc. The result appears in Table VI.: — TABLE VI.
June loth to 20th.
12 Inches.
13 Inches.
14 Inches.
15 Inches.
Hand used.
Deviations from me- Right.
Left.
dian line — 2 to 6 inches to 10 cases 15 cases 4 cases 2 to 6 inches to - 35 — Same conditions with colour stimulus.
— — — — 15 2 Experimental. 63 This table shows that deviation to the left in front of the body only called out the right hand to greater exertion, while the left hand fell into still greater disuse. This seems to show that dextrality is not derived from the experience of the individual in using either hand predomi- nantly for reaching, grasping, holding, etc., within the easiest range of that hand. The right hand intruded regularly upon the domain of the left.
Proceeding upon the clew thus obtained, a clew which seems to suggest that the hand preference is influenced by the eye stimulus, I introduced hand observations into a series of experiments which I was making at that time on the same child's perception of the different colours; think- ing that the colour stimulus which represented the strong- est inducement to the child to reach, might have the same effect in determining the use of the right hand as the increased distance in the experiments already described. This inference is proved to be correct by the results given in Table VII.: — TABLE VII.
Colour stimulus, f Hand Right. Left. Both. \ May 23d to It should be added that in all cases in which both hands are said to have been used, each hand was called out with evident independence of the other, both about the same time, and both carried energetically to the goal. In many other cases in which either right or left hand is given in the tables, the other hand also moved, but in a subordinate and aimless way. There was a very marked difference between the use of both hands in some cases, and of one hand followed by, or accompanied by, the other in other 64 The Origin of Right-handedness.
cases. It was very rare that the second hand did not thus follow or accompany the first; and this was extremely marked in the violent reaching for which the right hand was mainly used. This movement was almost invariably accompanied by an objectless and fruitless symmetrical movement of the other.
The results of the entire series of experiments on the use of the hands may be stated as follows, mainly in the words in which I reported them summarily some time ago 1. I found no continued preference for either hand as long as there were no violent muscular exertions made, (based on 2187 systematic experiments in cases of free movement of hands near the body: i.e., right hand, 577 cases; left hand, 568 cases, — a difference of 9 cases; both hands, 1042 cases; the difference of 9 cases being too slight to have any meaning); the period covered being from the child's sixth to her tenth month inclusive.
2. Under the same conditions, the tendency to use both hands together was about double the tendency to use either (seen from the number of cases of the use of both hands in the statistics given above).
3. A distinct preference for the right hand in violent efforts in reaching became noticeable in the seventh and eighth months. Experiments during the eighth month on 1 Science, XVI., Oct. 31, 1890; discussed by James, Science, Nov. 8, 1890, by Dr. J. T. O'Connor, Ibid., XVI., 1890, p. 331, and by myself, Ibid., XVI., Nov. 28, 1890. The results are quoted in full in A^ature, Nov. 13, 1890, and in part in the Illustrated London News, ^^.u. 17, 1891. See discussions of them also in Zeitsch. fiir Psychologie, II., 1891, p. 239; Wilson, The Right Hand: Left-handedness, Y>Y>- 128-131; Revue Scientifique, 1891, II., p. 493; Mazel, Revue Scientifique, 1892, I., p. 113. Both writers in the last-named journal cite these experiments wrongly as Wilson's.
ExperimeiitaL 65 ExperimeiitaL 65 this cue gave, in 80 cases: right hand, 74 cases; left hand, 5 cases; both hands, i case. This was true in two very distinct classes of cases: first, reaching for objects, neu- tral as regards colour (newspaper, etc.), at more than the reaching distance; and, second, reaching for bright col- ours at any distance. Under the stimulus of bright colours, from %6 cases, 84 were right-hand cases and 2 left-hand. Right-handedness had accordingly developed under pres- sure of muscular effort in the sixth and seventh months, and showed itself also under the influence of a strong: colour stimulus to the eye.
4. Up to this time the child had not learned to stand or to creep; hence the development of one hand more than the other is not due to differences in weight between the two longitudinal halves of the body. As she had not learned to speak or to utter articulate sounds with much distinctness, we may say also that right- or Icft-handcdness may develop while the motor speech centre is not yet func- tioning. Further, the use of the right hand is carried over to the left side, showing that habit in reaching does not determine its use.
5. In most cases involving the marked use of one hand in preference to the other, the second or backward hand followed slowly upon the lead of the first, in a way clearly showing symmetrical innervation of accompanying move- ments by the second hand. This confirms the inference as to such movements drawn from the phenomena of mirror-writing, etc., by Fechner and E. H. Weber.^ ^ I do not find, therefore, that these experiments warrant the negative in- ference on this question which Miinsterberg has drawn from them: Beilrage ziir Exp. Psych., Heft IV., p. 197.
66 The Origin of Right-handedness, § 2. Theoretical.
I. Some interesting points arise in connection with the interpretation of these facts. If it be true that the order of rise of mental and physiological functions is constant, then for this question the results obtained in the case of one child, if accurate, would hold for others apart from any absolute time determination. We would expect, there- fore, that these results would be confirmed by experiments on other children, and this is the only way their correct- ness can be tested.^ If, when tested, they should be found correct, they would be sufficient answer to several of the theories of right-handedness heretofore urged. The phenomenon can- not be due, as I have said, to differences in balance of the two sides of the body, for it arises before the body begins to stand erect. It cannot be due to experience in the use of either hand, since it arises when there is no such differ- ence of experience, and since the hand preferred is used, as a matter of fact, for purposes for which in experience the other would be altogether more convenient.^ The rise of the phenomenon must be sought, therefore, in more deep-going facts of physiology than such theories supply.
If, on the other hand, heredity be brought to the aid of 1 Vierordt says concerning such experiments: " Adequate observations are wanting on the grasping movements of the infant's left and right arm — a kind of observation which would be of the first importance for this inquiry," Physiologie des Kindesalters, p. 428; and Wilson: "Only a prolonged series of observations, such as those by Professor Baldwin already noted, made at the first stage of life, and based on the voluntary and the unprompted actions of the child, can supply the needful data," Lefl-.kandedness, p. 209.
2 An additional point, which I think is true, is that a right-handed child learns to shake hands properly — using the more inconvenient hand across his body — more easily than the left-handed child.
Theoretical. 67 these 'experience' theories, it is possible to claim that, as structure is due to function, experience of function must have been first in race history; and only thus could the modification in structure which is now sufficient to produce right-handedness in individual cases have been brought about. On the other hand, if we go lower in the animal scale than man, analogies for the kinds of experience which are urged as reasons for right-handedness are not present; animals do not carry their young, nor pat them to sleep, nor do animals shake hands! It must therefore be shown that animals are right- or left-handed, or that they differ in some marked respect in regard to function, in their nervous make-up, from man. Admitting the need of meeting these requirements; admitting again that we have little evidence that animals are dextral in their func- tions; admitting also the known results as to the control of the two halves of the muscular system by the opposite brain hemispheres respectively; admitting further that the motor speech function is performed by the hemisphere which controls the stronger side of the body, and is adja- cent to the motor arm centre in that hemisphere; and admitting, finally, that the speech function is one in which the animals have little share — all these admissions lead us at once to the view that there is a fundamental connec- tion between the rise of speech and the rise of right- handedness.^ 1 This much has been before surmised by Mazel, Revue Scientijique, 1892, I., p. 113. He makes no attempt, however, to account for the association, except by calling both functions expressive. Mr. F. II. Gushing has sent me a paper on 'Manual Concepts' (^American Anthropologist, V., 1892, p. 289) in which he gives interesting evidence from philology and race customs among various peoples of the direct influence of hand movements upon spoken and written language. He finds evidence that the Zuni and Roman numeral 68 The Origin of Right-handedness, Looking broadly at the methods of nervous and mus- cular development, and accepting all the results of neu- rology we are able to gather, we may say that in the differentiation of functions in the animal series certain principles may be recognized: i. The deep-seated vital functions represent least nervous differentiation, as is seen in the simple organs known as the lower nervous centres. 2. New symmetrical functions give a differential or two- fold organic development, the great instance of which is found in the cerebral hemispheres. 3. New asymmetri- cal or unilateral functions find their counterpart each in one of three kinds of nervous adaptation: {a) co-ordination of the hemispheres in a single function — i.e., functions which are crippled if either hemisphere is damaged; iU) co-ordination of particular functions in each hemis- phere^/.^., functions which are not crippled unless both hemispheres are damaged; and {c) co-ordination of par- ticular functions in one hemisphere only — i.e., functions which are crippled only if one selected hemisphere is damaged. All these kinds of co-ordination exist.
It is easy to see that both speech and right-handed func- tion belong under the last head of the last class — co-ordi- nations of particular functions in one hemisphere only — sounds are derived from hand words, and their numeral graphic signs are transcribed hand positions. It would be interesting also to inquire how far the right hand is predominant in gesture and sign languages, which precede articulate speech. Gushing points out that the left hand is usually a passive instrument which is manipulated actively by the right. The best report on sign-language is that of Mallery in Report of the Bureau of Ethnology, I., i88r, and the best discussion of the phenomenon is by Romanes, Ment. Evolution in Man, pp. 104 ff. I have asked Mr. Lester Jones, Fellow of Princeton Col- lege, to examine Col. Mallery's detailed reports of the actual signs employed in the sign-languages of the North American Indians, tabulating the cases in which either hand is used alone or predominately. I give Mr. Jones' results in Appendix B, with some remarks upon their value for our present inquiry.
Theoretical. 69 and that they belong in the same hemisphere. Why is this? What have they in common?
A very essential kind of hand movements are the so- called 'expressive' movements, meaning those which serve to convey a meaning, or express a state of consciousness. Of course, speech is par excellence the function of expres- sion. It is further only a part of the position upon which the psychological theory of expression is based, that all movements are in a sense expressive, and that details of expression and its relative fulness are matters of co-ordi- nation. Now, this co-ordination has attained its ripest and most complex form, apart from speech,iin movements of the hand. Upon this view it is easy to hold that right- handedness is a form of expressive differentiation of move- ment, and that it preceded speech, which is a further and more complex form of differentiation and adaptation.
The neurological basis upon which this hypothesis rests is adequate, and affords a presumption as to the psycho- logical development as well. The facts I have now given for the first time, go some way to support the view: 1. Right-handedness arose before speech in the child H.
2. Imitation by the hand of movements seen arises before articulate imitations of sounds heard; " this in spite of the fact that hearing, in its development in the child, becomes perfect before sight. 3. Characteristic differences in chil- dren in respect to their general mobility of arm and hand, manual skill, and quickness of manipulation, extend also to speech. As compared with my other child, E., the first- born, H., is remarkably agile and motile generally in her ^ See physiological evidence, below, pp. 422, 424.
2 Below, Chap. VI., § 4. It is interesting that of both hand and speech movements the latest to be lost in disease are those involved in the so-called ' mimicry ' of movement and in imitative speech.
70 The Origin of Right-Jiandedness.
temperament; and her speech development was relatively- much earlier and more rapid.
It is further interesting to note that musical ability is associated with speech ability — a connection which would be expected when one takes due account of the expressive character and function of music. As far as theories of the rise of musical expression have gone, they unite in finding its beginnings in the rudimentary emotional ex- pressions of the animals. The singing of birds is undoubt- edly connected with their mating instincts. Pathological cases also show a marked connection between musical exe- cution and speech, to the extent that, while musical defect almost invariably involves speech defects, the reverse is much less generally true — a fact which confirms the view that music is an earlier form, but still a form, of expressive reaction.