Mental Development in the Child and the Race
Chapter 4: The Origin of Right-Handedness
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§ 1. Experimental
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 this subject.[1] Among these theories certain may be men-
(57)-tioned with regard to which my experiments were conclusive. 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 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 care-
(58) fully enforced. She was carried about in arms very little, 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 conditions 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 Experiments | Right Hand | Left Hand | Both Hands |
| 1890.February 10th to March 15th | 30 | 744 | 173 | 166 | 405 |
| March 15th to April 14th | 25 | 623 | 134 | 141 | 348 |
| April 14th to May 14th | 25 | 546 | 213 | 130 | 203 |
| May 14th to June 19th | 16 | 274 | 57 | 131 | 86 |
| Total | 96 | 2,187 | 577 | 568 | 1042 |
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.
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I then conceived the idea that possibly a severer distance 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 resulting from the setting of the larynx rush of blood
to the head, seen in Hushing of the face, etc
and flow of urine). Table IV. gives the results; the number m each series was
intentionally made very small, from one to twelve, m order to avoid fatigue:
Table IV
| Date | No.of Series | No. of Trials | Right Hand | Left Hand | Both Hands |
| 1890. May 26th to June 10th | 32 | 80 | 74 | 5 | 1 |
The same cases, distributed according to distance, give us Table V.: --
Table V
| 12 Inches | 13 Inches | 14 Inches | 15 Inches | |
| Right Hand | 29 | 10 | 33 | 2 |
| Left Hand | 5 | -- | -- | -- |
| Both Hands | 1 | -- | -- | -- |
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 m reaching straight before her within the easy reaching
(60) 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 objects 12 to 15 inches distant. For the greater distances, the left hand was used in only five cases as against seventy-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 exposure of the stimulus to the right or left, aiming thus to attract the hand on one side or the other, and so to determine whether the growth of 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 10th to 20th | 12 Inches | 13 Inches | 14 Inches | 15 Inches | Hand Used | |
| Deviations from median line | Right | Left | ||||
| 2 to 6 inches to left | 10 cases | 15 cases | 4 cases | -- | 35 | -- |
| 2 to 6 inches to right | 2 cases | 3 cases | 1 case | -- | ||
| Same condtions with colour stimulus | -- | -- | -- | -- | 15 | 2 |
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 .
(61) The right hand intruded regularly upon the domain of the left.
Proceeding upon the clue thus obtained a clue 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; thinking that the colour stimulus which represented the strongest 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, 10 to 15 inches | Hand | Right | Left | Both | May 23rd to June 19th |
| Number of cases | 86 | 2 | - |
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 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
(62) use of the hands may be stated as follows, mainly in the words in which I reported them summarily some time ago. [2]
I. 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 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, neutral as regards colour (newspaper, etc.), at more than the reaching distance; and, second, reaching for bright colours at any distance. Under the stimulus of bright colours, from 86 cases, 84 were right-hand cases and 2 left-hand. Right-handedness had accordingly developed under pressure of muscular effort
(63) 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 left-handedness may develop while the motor speech centre is not yet functioning. 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 movements 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.[3]
Endnotes
- Cf. Vierordt's remarks, Physiologie des Kindersalters, 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 colleague and friend Sir Daniel Wilson.
- 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 Nature, Nov. 13, 1890, and in part in the Illustrated London News, Jan. 17, 1891. See discussions of them also in Zeitsch. für Psychologie, II., 1891, p. 239; Wilson, The Right Hand: Left-handedness, pp. 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. For later discussions of these and the colour experiments, see the child-study literature generally.
- I do not find, therefore, that these experiments warrant the negative inference on this question which Münsterberg has drawn from them: Beiträge zur Exp. Psych., Heft IV., p 197.
§ 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, therefore, that these results would be confirmed by experiments on other children, and this is the only way their correctness can be tested. [1]
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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 cannot 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 difference 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. [2] 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 these 'experience' theories, it is possible to claim that, as structure follows function, experience of function must have been first in race history; and only then would 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;
(65) admitting again that we have little evidence that animals are dextral in their functions; 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 adjacent 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 connection between the rise of speech and the rise of right-handedness. [3]
Looking broadly at the methods of nervous and muscular development, and accepting all the results of neurology 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
(66) functions give a differential or twofold organic development, the great instance of which is found in the cerebral hemispheres. 3. New asymmetrical 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; (b) co-ordination of particular functions in each hemisphere i.e. functions which are not crippled unless both hemispheres are damaged; and (c) co-ordination of particular 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 function belong under the last head of the last class co-ordinations of particular functions in one hemisphere only 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 expression. 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-ordination. Now, this co-ordination has attained its ripest and most complex form, apart from speech,! in movements of the hand. Upon this view it is easy to hold that right-handedness is a form of expressive differentiation of movement, and that it preceded speech, which is a further and more complex form of differentiation serving the same utility.
The neurological basis upon which this hypothesis rests is
(67) adequate, and affords a presumption as to the psychological development as well. The facts which are given in these pages 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;1 this in spite of the fact that hearing, in its development in the child, becomes perfect before sight. 3. Characteristic differences in children 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 temperament; and her speech development was relatively much earlier and more rapid.
It is interesting also 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 expressions of the animals. The singing of birds is undoubtedly connected with their mating instincts. Pathological cases also show a marked connection between musical execution 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.
Late observations also show, as far as they are sufficient, that the centre for music expression is also located normally in the left hemisphere for right-handed persons. Oppenheim
(68) reports a case [6] 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,' [7] 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 cases of motor aphasia in which execution is preserved. Further, Frankl-Hochwart declares that no cases are recorded of amusia from lesion in the right hemisphere, [8] and Starr says of a patient of his: [9] " My patient is right-handed, and music does follow speech in being unilaterally located; . . . it is well proved that the musical faculty is one-sided in location." Despite these positive 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 ? 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 gesture plays an important
(69) part in assisting speech; and in all cases where a vocabulary is scanty or imperfect, gesture 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."
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 variation' 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. [10] As an extreme example, fancy a bird become dextral in its flight. [11]
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,
(70) 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 find, however, in the habits of simians any ground for believing that there has been a form of unilateral stimulation 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 one of the reasons the monkeys 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 advantageous dextrality would inevitably arise and persist as soon as the habits of life were not such that more important functions, such as locomotion, tended to suppress them and restore bilateral equilibrium.[11] There are, as far as I know, very few published observations of fact in regard to simian or animal dextrality.[12]
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It is likely, therefore, that right-handedness in the child is due to differences in the
two half-brains, being always associated with speech, 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 cultivation of the other hand may, as the child grows up,
diminish or destroy the disparity between the two. And this inherited brain one-sidedness
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
(72) 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 dynamogenic method of experimentation. It will be remembered that in the formula [14]
[insert 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
[insert formula]
but, by the general law that distance decreases influence,
Insert formula
consequently,
[insert formula]
Again, we find from the experiments that
[insert formula]
but
insert formula
consequently
insert formula
the same result as (3).
So it seems from both of the experiments that
(73) right-handedness varies inversely as the dynamogenic influence of the stimulus, 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 supposed 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 the organic conditions) 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 stimulus, would have the same effect, without the central reinforcement, and also bring out the right hand. [15] 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 interpre-
(74) tations undoubtedly result, in the case of the child, in my opinion, from associations of visual indications of distance with sensations of hand and arm movement. And I find that this association gives rise to three determinations all matters of experience and all becoming remarkably refined (1) the safe-reaching distance (use of either hand or both); (2) the uncertain-reaching distance (use of right hand); and (3) the impossible-to-reach 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,[16] since I have made no observations, and your sense of what is likely in this regard seems
(75) to me to have great weight), the way I represent the matter to myself is thus: The child originally responds to all optical excitements which strike his attention 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 bilateral 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 dynamogenic effect of distance (d in the formula) is not natively provided for, as is that of quality (q, 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 present 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 sensorimotor 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 involving distance. And it is easy to see what becomes of the formula as soon as association gets to be a little complex; for d, we must substitute a symbol to stand for the central influence as a whole, say phi; and of course with increasing complexity of experience the meaning of phi becomes more and more
(76) recondite. With adults, therefore, such a formula would be in most cases nothing more than tautology.[17] With infants it
(77) remains useful only for 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 experiments 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 chapter.
Endnotes
- I do not find, therefore, that these experiments warrant the negative inference on this question which Münsterberg has drawn from them: Beiträge zur Exp. Psych., Heft IV., p 197
- 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 Der 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," Left-handedness, p. 209.
- 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.
- This much has been before surmised by Mazel, Revue Scientifique, 1892, I., p. 113. He makes no attempt, however, to account for the association except by calling both functions expressive. Mr. F. H. Cushing has sent me a paper on 'Manual Concept' (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 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. Cushing 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., 1881, 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 College, 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 predominantly. I give Mr. Jones' results in Appendix B, with some remarks upon their value for our present inquiry.
- See physiological evidence, below, pp. 400 ff.
- See 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.
- Charit&eactue Annalen, XIII., 1888, p. 286.
- Cf. Chap. XIV., below, for further exposition of the mechanism of speech and the music function.
- This means that all cases noted have been right-handed. Deutsche Zeitsch. für Nervenheilkunde, 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.
- For this reason the human leg, as Brown-Séquard says, is not as one-sided as the arm. Any great unevenness would produce lameness and relative incapacity.
- 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.
- 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 education; the evidence against Wilson's view, apart from my present results, is well put by Mazel, loc. cit.
- 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, 1871. 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
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 preliminary period of
left-handedness a view to which my Table III., above, gives some support might have its
explanation in the hypothesis of the repetition of phylogenetic development in the
individual child. My own experience with parrots now (1906) confirms Vierordt. My birds
stand on the right and hold the food with the left claw.
It is evident that on this theory of spontaneous variation any change which produced a permanent organic superiority of one hemisphere would 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 (ct. the note of Dr. J. T. O'Connor apropos of my experiments in Science, XVI., 1890, p. 331). It is an interesting inquiry whether this arterial arrangement is reversed in left-handed persons. Wilson cites two cases in which there was no such correspondence (loc. cit., p. 179).
- Above, Chap. II., § 3.
- On this point, Professor William James writes (Science, Nov. 14, 1890 p. 295), a propos of my experiments when first announced: "These observations seem very interesting, as showing how strong (attractive) stimuli may produce 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 particular channel which is ready for it.
- In view of my letter in Science, NOV. 28, 1890, P. 302. He adds, however, after
the above quotation: " Although I have made every possible concession 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, if it be a fact
that infants 'grasp at the moon' with either hand indiscriminately, the 'moon' standing
for any object at any distance. 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. cf.. Lloyd Morgan's instances of 'probably instinctive' actions, in Habit and Instinct, Chaps. II., IV., where he cites these results. - The only way to experiment on volition, accordingly, is by using comparative
stimulations of no meaning or association, or by keeping the association 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, 18,02, p- 51 see 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 explained 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. Professor 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 .. 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 not 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 doing 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 pathways of voluminous discharge for right-hand movements opened up by earlier more successful movements, and, at the same time, other pathways for the same discharges when less 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 e' large hole for the cat and a little hole for the kitten' an arrangement which Professor James argues against, at least in one connection (Princ. of Psychology, Vol. I., p. 592). But that the child does extend 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).
