CROSSED LATERALITY - BMJ

CROSSED LATERALITY

A STUDY IN ITS SIGNIFICANCE AND TREATMElWNT IN ORDINARY SCHOOL LIFE

BY

ROBERT A. H. PEARCEFrom the China Inland Mission School, Kuling

(RECEIVED FOR PUBLICATION JANUARY 20, 1953)

All paired muscle systems are represented in thebrain by paired controlling centres. Dominance, orleading control of the function, may be entirely left-sided, in which case the organs controlled aredominant on the right side, or entirely right-sided.If some centres are on the left and some on the rightside of the brain, the condition is called crossedlaterality.The dominance may be fixed, and diagnostic

methods give no variation in results. In somechildren there is less fixity, one or the oppositecentre taking control according to whim or circum-stance.

These investigations were provoked by the obser-vation of educational problems arising in a schoolof 150 to 200 children of both sexes between theages of 6 and 16. The observations and investigationswere carried on over a period of four years. Theexaminer knew all the children intimately, and livedamong them continually. Thorough physical ex-aminations were made at intervals of approximatelynine months. Intelligence was measured and re-measured, using Terman and Merrill's tests, andRaven's progressive matrices. The teaching staff ofthe school used to meet regularly and frequentlyfor discussion of the progress, educational problemsand conduct of each child. In the capacity of SchoolMedical Officer I attended all such meetings. Therewere unrestricted opportunities for investigation ofthese problems.During the work report meetings it was noticed

that some 40% of the children, at one time oranother, presented some difficulty or failure ineducational attainment. A further search revealedthat 70°' of these children had some type of crossedlaterality. Viewed from another aspect it was knownthat 4700 of the children in the school had crossedlaterality, and of these 8500 were in the group whoexperienced difficulties in school work.

The work here recorded was planned to discover:(1) Symptoms arising because of crossed laterality:(2) the effect of these symptoms on education;(3) the mechanism whereby these symptoms are pro-duced; (4) why some cases of crossed laterality wereasymptomatic; and (5) effective means whereby thehandicap of crossed laterality might be overcome.

The SymptomsReversal of units in a series was the most promi-

nent and basic phenomenon observed. This wasfound in any of the 'three R's' at any age. The childwas never conscious of the error until it had beenmade. The symptoms to be described are notobserved on every possible occasion. In differentchildren they are present with varying frequency andpersistence, depending upon the nature and thefixity of the irregularity, and upon what com-pensations the child has developed. Other factorswhich influence the appearance of symptoms areemotional tension at the time of examination; thetype of teaching which the child has experienced,and the associated mental stress; the intelligence;and the speed with which puberty is being attained.No child will show all the symptoms observed, buteach type of 'crossing' is associated with certainsets of symptoms. These symptoms do not occurin children without irregular dominance. Any childmay make a mistake, and in the course of ordinaryprobability any particular mistake may be made.Those children who have these forms of irregulardominance show these symptoms frequently andpersistently. Further, they find difficulty in learningto correct the mistakes, for the error occurs uncon-sciously.

It is not at all uncommon for children who arejust learning to write to reverse letters, as b for d,or vice versa. Normal children learn the correctform quickly and without difficulty. Children with

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ARCHIVES OF DISEASE IN CHILDHOOD

irregular dominance are slow to make the correction,not readily appreciating the error. They have amarked tendency to repeat the error unconsciously.In older children the error may appear so that theyseem to make careless mistakes in compositions andarithmetic. One can look upon a letter or figure as adiagram. More complicated diagrams have beenprepared, and reversal of units of these mayfrequently be found when these are reproduced bychildren with irregular dominance. For example,this diagram (from Terman and Merrill's testsForm L 9 years) copied from visual memory may bereproduced with the corner units reversed thus:

EF

When reading, reversal of the letters of a wordmay make something unpronounceable and mean-

ingless, or occasionally a word that does not fit thesense. In the former instance, reading will be slow,and the child appears to stumble at small words.In the latter case the wrong word is read, delayingthe perception of content, or if read aloud, the childis embarrassed and appears to others to be stupid.As an example, the child reading 'He saw a plum'may perceive and read 'He was a plum'. A similarfault is found in arithmetic, for the child reads or

copies the figures of a problem in reverse, as 54 for 45or 729 for 792.

Perception by hearing leads to reversal symptomsless frequently than if perception is by vision, forthe opportunity is less. I have known it to occurwhen a child looks for a hymn that has beenannounced during a service of worship if he cannotsee the hymn board.

It is characteristic of children learning to write,who have crossed dominance of eye and hand, thatif the accepted normal standards of writing-position of person or paper and pencil-are rigidlyenforced, the resulting script is poor. If the childrenare left alone to write as they please the script maystill be poor, but they will twist the paper or thehead. The children do not know why they do this,but all affirm that it is easier for them to write inthis 'awkward way', and a diagnosis of 'poormuscular control' is frequent.

Children who use a left foot dominantly show no

closely related symptom, but may provoke a laughfrom their fellows who consider the foot workstrange and awkward. But if the ability to kick wellwith a left foot wins for such a child acceptance as

having a special ability, he will avoid the emotional

upset commonly seen to follow the symptoms ofirregular dominance.

Children having complete left dominance showsome of these symptoms, but with characteristicdifferences. Reversal mistakes in reading occur, butnot in listening. Some prefer to write along linesthat are oblique to the body. The use of the writingleft hand above the line of script is only a means bywhich what has been written may be seen, the handnot then obstructing the view. Not all children usingthe left hand are completely left-handed; some havecrossed laterality, and show the symptoms notedabove.

Attempts to force the child to use dominantly afunction which is not naturally dominant will causesymptoms to arise from the induced crossing, andalso certain other evidences of cerebral turmoil.Symptoms arising thus are minimal when the cross-ing is not fixed, and when intelligence is high. Themost widely known symptom resulting fromattempts to change dominance is deranged speech.This can vary from complete aphasia to varyingdegrees of stammering. Other signs of nervous upsetare also seen-not in themselves pathognomonic-such as enuresis and encopresis.The emotional upsets that develop because of

these symptoms are not isolated events but grow asthe errors recur. The form which they take willdepend upon factors such as age, development,speed of growth and intelligence. The followingstory is typical: The little child learning to write hasa very poor hand, and the teacher finds that effortsto bring improvement meet with little success.Mistakes in reading recur so persistently that theteacher naturally begins to suspect that the child'smental capacity is not equal to the appointed tasks.Should he read silently, the content is gained tooslowly: should he read aloud, errors are made oversmall words, and he becomes a source of merrimentto his fellows. In arithmetic the persistent mistakesare labelled 'careless'. In consequence we find thechild is frequently embarrassed in his class, andbegins to echo his teacher's suspicion that he ismentally slow. He says, 'The harder I work, theworse I do.' It is easy, even reasonable, to cease totry hard and to drop into lazy habits. These childrenare difficult and often exasperating. No child of highintelligence fails without suffering, for he is consciousof ability and rebels against the suggestion that heis 'dumb'. He either becomes lazy and difficult orembarrassingly nervous, failing to keep pace withothers, in spite of what appears to be tremendouseffort.How deeply this emotional trauma affects the

child depends upon inherited physical factors and

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CROSSED LATERALITYupon intellectual capacity as well as upon theenvironment. The emotional conditions observedcan be classified under certain factors thus:

High Intefligence and Quick Develoment. If theirregularity is not fixed there is little of note exceptthat the child learns more slowly than a similar childwithout the handicap.

If the irregularity is fixed, natural compensationsdevelop with speed depending on the type of crossingand the intelligence. These children respond tosympathetic, helpful handling and symptoms areovercome. In cases where there has been othereducational lack, or where there has not been goodteaching, some symptoms will persist. The lack ofprogress will be covered by indifference leadingsometimes to actual laziness.

High Intelligence and Slower Development. What-ever the fixity of the irregularity, these children arediffident. Natural compensations occur moreslowly, and the child is constantly finding frustra-tion. These children do not make progress as quicklyas one might expect from knowledge of the I.Q.

Average (and Lower) Inteigence, with QuickDevelopment. Symptoms are definite. Compensa-tions are only slowly attained. Persistent mistakesstimulate a rebellious attitude towards the teacher,and methods of escape are planned and effected.

Average (and Lower) Intelligence with Slow Develop-ment. Symptoms are definite. Compensations areslowly attained. These children tend to be vindictive.The frequent mistakes and slowness to learn will beblamed upon their teachers.

Emotional disturbance is probably of greaterimportance ultimately than educational backward-ness. When a child has failed to attain an adequatestandard of reading and writing he will find his wayinto some gainful occupation which is not dependantupon these abilities. If he has grown up with feelingsof frustration, inferiority and diffidence, these willprove ever present trials in any walk of life.

Diagnosis of Ear, Eye, Hand and FootDomce

It is reasonable to speak of dominance of one ofa pair of these functions only if each of the organsconcerned is practically normal. The ordinaryvariations between the eyes, due to differences ofrefraction, do not determine dominance. The follow-ing methods have been found to give consistentresults. When seeking to determine dominance it isessential that the child be absolutely at ease, happyand generally interested and yet ignorant of the

object of the test. It is a good plan, therefore, tospace out the tests at different times in the course ofa physical examination, and also to use a variety oftests.

Ear. During examination of the ears for hearingacuity the child is made to stand in front of the tableupon which rests a watch on a cushion. He is askedif he can hear it. The watch is then covered by acloth, or placed in a box, and the question repeated.If the child is not able to hear the watch, he is toldto get closer to it, and still closer until he can. Itwill be observed that as the child bends or approachesthe watch, he will bring either the right or the leftear nearest. This is the dominant ear. This test mustbe varied in form from time to time and from childto child.

Eye. Many tests have been described for thedetermination of eye dominance. Some have provedunreliable in small children because of difficulty ingaining their cooperation. The following tests andsimple variations have been found reliable. A smallbright object on the far side of the room is observedby the child through a small circular hole aboutW in. in diameter in a card held at arm's length. Theexaminer stands behind the child and observes theline object-hole-eye. This eye will probably be thedominant eye. While still in that position, the othereye is shaded and the child asked if he can still seethe object. If the original line has been notedcorrectly by the examiner he will answer in theaffirmative. The presumed dominant eye is nowshaded. The child will say that he does not see theobject, and will move the card until the other eyetakes up the line. There is more difficulty in liningup the non-dominant eye. The card will be movedup and down and round about until it is in position,an action quite distinct from the quick way in whichthe dominant eye is lined up. This test is veryreliable, but too difficult for small children.The following test I have found acceptable to a

small child; it gives satisfactorily consistent resultsand can be modified almost indefinitely accordingto circumstances. On the hillside opposite to myconsulting room there was a wooden shack whichhad three windows of different sizes. The child wasgiven a cardboard tube, told to pretend that it wasa telescope and to look at the 'large-sized window,the middle-sized window and the smallest window'to see if any of the bears could be seen. The childuses the dominant eye. A kaleidoscope, a toytelescope and such playthings can be used effectively.

During a test for visual acuity the child is given asmall refraction mirror with a central hole. He istold to use this looking from the black side through

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the small hole at the lower letters on the eye chartto see if they appear blacker. He will use thedominant eye, and in most cases make no movementto use the other, indicating that his thoughts are onthe letters rather than the eye. The result is thereforethe more likely to be reliable.

Hand. If a small child is given a pile of blocksand is told to build a tower, the highest blocks,whether the pile is of single or of many columns,will be placed with the dominant hand, for that canbe used more delicately and with better control.Older children, able to write, will use either adominant right hand naturally, or a right handwhich has been 'changed', or a dominant left hand.The child then takes the pencil in the other handand endeavours to write. The dominant right-handed child holds the pencil awkwardly and doesvery poor script or none at all. The 'changed' childtakes the pencil with the left hand, holds it easilyand makes a presentable script. The true left-handedchild finds the use of the right hand as difficult ashis right-handed fellow does the left hand. Thedominance of eye and hand together may be shownif a child is asked to thread a needle. He willobserve the eye of the needle with the dominant eye,and may even close the other eye. He will hold thethread in the dominant hand, for this hand will haveto make fine movements, and the needle in the non-dominant hand, for no movement is required at all.

Leg. When the little child has built his tower ofblocks he is given a small wooden ball, which isplaced on the floor 6 or 10 feet away. He is toldto kick the ball so that it knocks the tower down.It is probable that he will have to make more thanone attempt. Accurate aim when kicking is obtainedonly by using the dominant leg. In older childrenthis may have become apparent already for thechild is known to be a useful left wing in football.Older children have been tested in the followingmanner. Standing on the far side of the room fromthe examiner, they are told to kick back to him aball he rolls to them. A child with a dominant rightfoot will do this with the right fooL The ball is rolledagain, but this time to the right of the child. He willstill return it with the right foot. The ball is thenrolled again to the left of the child, and the childwill turn so that he will kick the ball back againwith the right foot. A child whose left leg isdominant does just the reverse at these differentstages.

Balance has been used to determine leg dominance,for the dominant leg or foot is used to restoreposition to the body when the balance has beenupset. This is best observed in the child's play. Any

test designed to upset the child's balance mayfrighten him if unexpected and so spoil 'rapport'between examiner and child. But if the child bewarned, he will not act naturally or unconsciously,and the value of the observation becomes question-able.As has been noted, observation in work and play

can be of great value, and is almost the only reliableway of tackling the problem in very young children.Some acts, such as the 'high jump' and digging, usea number of organs, and can be used in confirmationof the results obtained by the specific tests.

Equivocal results indicate that dominance in oneof a pair is not fixed. If modifications of the test aremade on different occasions it will be seen whetherthere is real lack of dominance, or whether theequivocal result is due to lack of understanding onthe part of the child. The lack of complete dominanceis revealed by the use of one of the organs concerned,but a readiness to use the other if that be moreconvenient. For example, one ear will be used. butif the child cannot hear, he may turn and use theother; one eye will be used, and then the other:one foot may be used to kick the ball back to theexaminer, but when the ball rolls nearer the otherfoot, this will be used as easily as the first. Suchresults are of importance, for they have a bearingupon prognosis of treatment.

Notation

The following notation has been found con-venient. The capital letter R and L indicate dominantfunction, as right or left (not cerebral centre). Wheneither of the paired organs may be used satisfactorily,neither being dominant but used according to thesubject's convenience, small letters are used, r and 1.But in these instances they will of necessity be inpairs, rl or lr. When the dominance is definitely onone side, but there is ability on the other, it isindicated thus, RI or Lr. The organs described arerecorded in the order, ear, eye, hand and foot. If,for some reason, the dominance of one of a certainpair cannot be determined, as for example if thesubject has a blind eye, the space in the series isnoted by a full-stop. When the position of the centreis not known its place is indicated by 0. If the typeof dominance is irrelevant to the argument, thisfunction is indicated by the oblique line /. Theposition of the speech centre is indicated by the useof R or L in brackets (R) or (L). This naturallyrefers not to the observed function but to the actualcerebral centre.For example, R R R R indicates that the subject's

ear, eye, hand and foot, are dominant on the right

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CROSSED LATERALITYside, the cerebral centre being on the left. L L R Rindicates that the subject's ear and eye are dominanton the left side, but that the hand and foot aredominant on the right. R L RI L indicates thatthough the right ear, left eye and left foot aredominant, the right hand shows more skill than theleft, but the left also has ability. L R (L) R Lindicates that dominant function of ear and footare on the left, and of eye and hand on the right.The speech centre is deduced by experiment to beon the left side of the brain.

Aetiology

A clue has been found to the development ofcrossed laterality from a study of family histories,The children in this series belonged to 70 families.All the cases of irregular dominance were found in57 of these families. Fresh cases of crossed lateralitywere found among other brothers and sisters of thesefamilies, not pupils of the school. Those childrenwho showed equivocal findings all had sibs withdefinite irregular crossing, and therefore showed thecondition in the family tree. Similarly, an isolatedleft ear dominance was found only in those familieswhere there were other types of crossed dominance.Complete and accurate family histories are rarely

obtainable, for diagnosis in an adult may be difficultor, if absent, impossible. Occasionally one can learnof relatives who were definitely left handed, or wereknown to have left dominance of eye or foot. Again,one hears of relatives in these families who wereknown to have shown symptoms, particularly badwriting, bad spelling, stuttering, or of having beenchanged from right to left handedness.The condition may arise spontaneously in one

of uni-ovular twins, one having complete rightand the other completely left dominance. Mostcommonly it is found that one or other or both

Family 1

of the parents have irregular or left dominance.Among the offspring complete left and completeright dominance or any type of crossing occurs.Occasionally I have found two or three children ina family with definite irregularities but with norelative known to have anything but the usual rightdominance. I have also noted apparently normalparents who have brothers or sisters affected. Theselatter two observations raise the possibility of thetransference of a recessive factor, but such instancesare the exception. An obvious family history is therule.The following family trees are typical of those

collected. Incompleteness is largely due to therelatives being scattered over four continents, andtherefore beyond examination, and sometimesunknown to the parent questioned. These symbolshave been used:

Condition not known: Male [] Female Q

Definitely unaffected

Definitely affected *Died young VJ @6

The letters by the symbols refer to description in thelegends of the individuals marked.

All subjects known to show any left-sided dominance,complete or incomplete, are regarded as 'affected' inthese pedigrees, and in this section of the discussion.

These five histories illustrate the conclusions regardinginheritance which have been confirmed by similarhistories of other families. Persons examined are indi-cated.

Families 1 and 2. Show inheritance through threegenerations.

Family 3. Shows persistence of genetic factor, in spiteof an apparently successful change of mother from right to

A. Known to use left hand and foot, but having righthand ability.

B. Known to use right hand and foot.C. As A.D. L L lr L. University graduate.E. R R R R. Knows of no symptoms in family.F. rl R R R. No symptoms.G. R R R R. No symptoms: clever.H. lr L R R age 6: early schooling very handicapped

by symptoms.J. L L L L age 4. Has had no schooling.D, E, F, G, H and J are the only individuals known and

examined.

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Family 2

L. L L R R. Stuttered as a child, fair ability, handi-capped by bad spelling.

M. R R R R. Poor ability but no symptoms.

A. Left handed.B. Thought to be right handed.C. D. E. Completely right, without

symptoms.n ~F. LLLL.'~G. Attempt vras made to change

l b n ~~~~dominance-failed entirely.G T H. Completely right, no symptoms.J. Lr R R R. Average ability,

very little trouble exceptenuresis.

N, 0 K. rl R R rI. Average ability:no symptoms.

N.O.P. No known symptoms, thought to be righthanded. Not examined.

C, D, E, F, H, J, K, L, M are the only persons knownand examined.

Family 3

A. Changed from left to right hand forwriting.

B. Left handed.C. Right banded, no known symptoms.

Very clever.D. Left handed aged 3.E. L R L R. Intelligent, but very poor

writing.F. Left handed. Family not known.G. School work sfow and poor. Blinks

continually. Right handed.H. Suffers with a nervous tic.E is the only individual known and

examined.

Family 4A. Left handed.B. RRRR.C. R R R R. High intelligence.D. LRRR.E. R L R R. Poor average I.Q. not yet at

school.F. RRRR.A, C, D, E, F all known and examined. History

obtained through F who was not veryfamiliar with her husband's family.

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Family 5.

bX~~~~0xa9

IFe;G OH *J

Family history obtained from K, L, M and N, who wereall unaffected.

F.G.H. known and examined, J. abroad, age 4.A. A left-handed bowler.B. Left handed.C. Able to read well, but would never read aloud.D. Left hand, changed to right and became bad in

reading and writing. Stuttered.

left handedness. Also illustrated the possibility of a childinheriting the condition through a parent not known tohave symptoms, and possibly without the condition.Family 4. Shows inheritance through an apparently

normal father, in whose family there is left handedness.Family 5. Left handedness is recorded in the families

of both parents (in the case of one, with very severesymptoms), though each parent is apparently normal.The mother, N., had lost the sight of the right eye throughan accident when aged 18 months.

Naturl Compensations for the Symptoms

How frequently the symptoms of crossed lateralityoccur depends on the extent to which compensatorymethods are developed. The presence and signi-ficance of these are unknown to the child in themajority of cases. They arise unconsciously, and aremost developed in children with high intelligenceand of fixed irregularity. Correct perception isobtained by multiplying the stimuli received. Thelesser the child's intelligence, the slower he will beable to compensate in this way.When the ear is used a smooth, soft monotone is

a single stimulus. If rhythm or emphasis be addedto the sound, the memory of music is also stimu-lated. The louder the sound heard, the more likelyit is that both ears will be used, and not the dominantear alone.The child looking steadfastly at a design he has to

reproduce from memory will sometimes be observed

E.

F.

G.H.J.

Backward in spelling and reading with symptomsof emotional upset through schooling.

L L Lr Lr. Average intelligence, backward at schoolbecause of very troublesome reversals.

R R R R. No symptoms.L R R R. No symptoms under ordinary conditions.Known to be left handed. Not examined because

of being abroad.

to move a finger as though following the pattern ashe will draw it. This addition of kinaesthetic memoryensures correct perception. Ocular perception issometimes corrected at a later stage. When the childperceives that what he has read does not make sensehe will re-read correctly. This depends entirely onhis mental ability. Slower children go to the stageof transferring the perception to speech. Then,having heard what they have said, the need to correctis known and effected. Just as loud sounds makeincorrect perception unlikely, so large visual imagesare more accurately remembered.A still different approach has been seen among

those children whose irregular dominance leads toincoordination of hand and eye. When writing theyturn the paper so that the line of writing is at anangle to the body. They find this easier and theirefforts more acceptable.

The Course of Crossed Iterdality Uninfluenced byTreatment

Crossed laterality has been brought to notice inrecent years, not only by careful observation, butbecause a greater opportunity for the developmentof symptoms as formal education has become moregeneral. Persons engaged in outdoor or manualoccupation are not subjected to the same mentalactivities as those engaged in more intellectual tasks,and do not show these symptoms. If the early

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schooling has been adequate the intelligent childunconsciously gains compensation for his handicap,and is almost without symptoms.

I have found no evidence that real change ofcerebral dominance ever occurs. If the dominantone of a pair of cerebral centres is destroyed beforethe age of 5 or 6, the other will gradually gaincomplete control of the function. At a later agefull fumction is never attained. When one of theorgans becomes useless a similar course will befollowed. In neither of these instances is the basicinherited pattern altered, nor are the geneticpotentialities of the individual changed.

Varities of Crossed Dominace Found in this SeriesGroups I and II. LRRR, 16 0%; RLL L

0 -6%. These are almost without symptom orhandicap in ordinary school life. Under artificialcondition reversal can be demonstrated fromreception by hearing to expression by speech orwriting.

Groupsm and IV. LLRR, 10-6%; RRLL0-600. The most serious symptoms occur in thesegroups.

GroupsVandVI. LRLR, 1 20°;RLRL,nonefound. Reversal symptoms occur in speech andwriting, but corrective mechanisms readily develop.GroupsVH and VII. L L R L, 1 20'; R R L R,

none found. Reversal symptoms occur in speechand writing, but corrective mechanisms readilydevelop.

Groups IX and X. R L R R, 14 600'; L R L L,0-60O. Serious symptoms occur as in groups HIand IV.

Groups XI and XII. R L L R, none found;L R R L, 0- 6o. Symptoms as in groups I and II.

A potential handicap was present therefore in

nearly 2800 of children in this series.Complete left dominance was present in 400 and

complete right dominance in 49 3 % of the childrenseen. The sex distribution was equally divided, bothamong the children with crossed lateral anatomyand the remaining children. There was a very slight,probably insignificant preponderance of malesamong those showing symptoms that could berelated to this condition.When the intelligence quotient is 120 or higher

evidence of crossed dominance is readily maskedby the child's unconscious development of com-

pensatory mechanisms.

Experiment InvestigationAlthough unconscious reversals occur spon-

taneously in ordinary school life, they can also beprovoked artificially. This was observed whilemaking intelligence tests with the material preparedby Terman and Merrill. In the course of repetitionof a series of figures it was found that a child withirregular dominance might reproduce all the digitsbut reverse the position of two. This error was notperceived by the child, who appeared satisfied thathe had done what had been required. Because oferrors of this kind a serious number of months ofmental age might be lost, vitiating the quotient. Byaccepting the series as correct, even though twounits were reversed, a quotient more in keeping withthe findings of other non-verbal tests was reached.Many series of figures and letters were prepared

for presentation to the child in these experiments.Care was taken that each should be a singlestimulus. Thus, letters like b and d were not placedtogether in a series, nor as terminal letters in con-secutive groups; letters in alphabetical sequence, andthose occurring together in spelling frequently, asg and h, or t and h, were omitted. Letters were notgrouped so that any word or well known acronymcould be assimilated, as W H Y C, or U N 0 X, orS T M W; all vowels were omitted because wordsor syllables might be formed. Letters which mightbe confused with other letters through similarity ofsound were not used, as j and k. The figure serieswere constructed so that there should be no sequenceor progression which might have been appreciatedby a bright child, as 2 8 3 4 7, or 1 2 4 8, or 2 3 7 8,or 4 1 8 5, and so on. Throughout the expenrmentsno child was given the same series twice. Fourteendistinct series of letters and figures were preparedfor each child, and if repetition were subsequentlyrequired another series would be constructed.The ability to reproduce a series depends upon

the mental age of the child. Three groups of threewere first presented; then three groups of five: threegroups of six; three groups of seven; and threegroups of nine. With figures it is known that amental age of 3 repeats three figures, of 41 fourfigures, of 7 five figures, of 10 six figures: series ofeight and nine figures are repeated by those havinga high adult standard of intelligence.

Letter series of similar length could be repeatedat about the same intelligence level. Reversal ofunits occurred unconsciously with those havingirregular dominance, even from the shorter series,but as soon as a series above the mental age levelwas reached, this type of error was replaced bycomplete confusion of the units repeated, in kind,number and order. The child became conscious oferror, and no useful purpose was served by pro-ceeding with the tests at these higher levels, for it

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caused the child to become embarrassed and spoiledrapport.The method of presentation was carefully planned

so that the child met a single stimulus. At a laterstage in the tests two single stimuli were simul-taneously applied. When hearing was to be used,the series was spoken to the child by the examinerin a soft regular monotone, at a rate approximatingto two units a second. A simple apparatus wasconstructed so that the child might view the seriesfor a similar length of time, after which it becamehidden. The letters were in block capitals, and bothletters and figures of a size corresponding to 6/6vision at 3 feet. Similar series were prepared so thatthey might be presented to the child vertically.

Expression was made to be a single effort. Whenwriting the child was told to write immediately andnot to repeat to himself, either before or whilewriting, the series. This was not always easy forsome children because of habits they had formed.It was observation of this difficulty and its effectswhich suggested the combination of expression;thus, the child would write what he had seen orheard, and then repeat it by speech without readingwhat had been written. And, alternatively, he wouldrepeat what he had perceived, and then write it.

These tests are time consuming, and the childeasily becomes fatigued. It was found best to keepeven the most intelligent no longer than 20 minutesat any one time and to complete the tests on subse-quent days.The findings are summarized in the table on

page 256.If the child s eyes are watched as he reads-a

mirror is placed in the plane of the book and theobserver stands behind the child they will be seento move in tiny jerks from side to side. If the righteye is dominant the eyes jerk towards the right; ifthe left is dominant, although the eyes are stillmoved towards the right, sudden movements in theopposite direction occur simultaneously with reversalof what is seen, or a stumbling in the reading. Whenpresented with a picture of a number of objects,none being a principal feature, the child who isright eyed will enumerate the objects from left toright, and the left-eyed child will do the reverse.The movement of the eyes may be known sub-jectively when travelling at speed in a train. Theright-eyed traveller, facing the way he is going, readsnotices or station names more easily if he looks overhis right shoulder than similar notices seen as helooks over the left. When he sits with his back tothe engine the opposite is true. But, if the travelleris left-eyed, all these observations are reversed. Inthe forementioned experiments it was found that,

while horizontal presentation of a series to the eyeresulted in reversals appearing, vertical presentationdid not do so. Children with the cerebral pattern/ L L/, and /L R/ find that they can write better andmore comfortably with the book on a slant. Thehand moves of necessity from left to right, but theeyes do not follow this direction naturally. By usingan oblique path the eye can maintain control overthe hand more easily. When a child writes a linesix inches long, parallel to the line of his shouldersand eighteen inches distant, the eyes must sweepthrough a horizontal angle of 20-. If the book isturned through an angle of 60- the horizontal sweepof the eyes is through 8^, and the vertical sweepthrough 16'. If now the plane of the book is de-pressed from the child through 45 the verticalsweep required of the eyes is now 104°.

The Mechanism of Reversal Symptoms as Deducedfrom Experimetal Fidings and Observed Natural

CompeationsDominance of a cerebral centre ensures that the

function of the corresponding muscle is delicate andaccurate. In the ear the tensor tympani controls thesensitivity of the drum to the pitch of the soundsought. Each ear may be completely sensitivethroughout the whole range of audible sounds, butthe child prefers to use one ear when listeningintently and so, presumably, the impression is morefixed on that side of the brain. Observations of eyemovements show the method by which reversaloccurs. Accuracy of vision is determined by use ofthe ciliary muscles, and so there is preferential useof a single eye when observation is made througha small aperture. Because of the optic decussation,visual perception is equal on each side of the brain.Similar delicacy of control is attained in both handand leg or foot movements through a dominatingcerebral centre. This is noticeable when a childbuilds a high tower of blocks, and when he attemptsto use the non-dominant hand for writing.The reversal symptom arises when what has been

perceived is expressed through the medium of adominant cerebral centre which is on the oppositeside of the brain from the dominant centre of percep-tion, as is shown in Experiment 1. Visual perceptionis not reversed in this way, for both sides of thebrain have been equally stimulated. When the eyesare required to observe and reproduce a series in adirection opposite to the natural movement, irregularmovement of the eyes will result in inaccurateperception, and consequently in inaccurate expres-sion. This is demonstrated in Experiments 3 and 4.

Speech is controlled from two cerebral centres.

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Experi- Dominance Patterns showing Reversal Types of Crossing accordingmnit No. Method of Reception Method of Expression Symptoms to Groups (page 254)

1 Hering Writing Right ear and left hand dominance and *ice I, II, In, IV, vH, XHversa

2 Hearing Speech Found sometines when ear and hand 1, H, III, IV, V, IX, X, XIIdonminance were opposite, and also whenear and eye dominance were crossed, eventhough ear and hand dominance were inagreement. This suggests that in such casesthe speech centre is situated in the cerebralhemisphere corresponding to eye domin-ance rather than in that related to thedominant hand

3 Sight W'riting With left eye dominance irrespective ofhand II, III. VII, IXdominance

4 Sight (horiz.) Speech With left eye dominance irrespective of hand II, III, VII, IXdominance

5 Sight (vert.) Writing None

6 Sight (vert.) Speech None

7 Hearing and sight (horiz) Writing None

8 Hearing and sight (horiz.) Speech None

9 Hearing Wnting then by speechReversals occur at the first as in Experi-

10 Hearing Speech then by writing ments 1, 2, 3, and 4

II Sight Writing then by speech If reversals occur at the first stage they are

12 Sight Speech then by writing

13 Hearing and sight (vert.) Writing None

14 Hearing and sight (vert.) Speech None

This is to be expected since the muscles used are inpairs. Confirmation of this is found in pathologicalprocesses. If a cerebral abscess occurs in the regionof a speech centre, speech will be completely lostwhen the presumed dominant centre has beendestroyed. But in early childhood speech will begradually regained as the opposite side takes overcontrol. But after the age at which cerebral anatomyhas reached full development, perfect speech willnot return. An opposite train of events is seen if thenon-dominant centre is destroyed by the abscess.

Since reversal symptoms. occur between ear andhand when the dominant centres are on oppositesides of the brain, it may be reasonably presumedthat reversal following the transference from ear tospeech indicates that the speech centre is on the side ofthe brain oppositefrom the dominant auditory centre.

In Experiments 5 and 6 it will be seen that withthe vertical presentation no reversals occur. So,when the child reads or writes along a line morevertical than horizontal the dominant left eye isafforded less opportunity to act irregularly.By combining the two main stimuli of hearing and

sight, as in Experiments 7 and 8, reversals are againavoided, even though each stimulus of itself mightlead to the symptom. The sound checks the move-ment of the eye, and prevents inaccurate perception.Then, accurate perception having been obtained at

the visual level, this corrects any tendency to reversefrom ear to hand or speech. In Experiments 13and 14, the vision, being accurate, corrects thetendency of reversal from ear to expression.

Experiments 9, 10, 11 and 12 were planned toshow the value of two forms of expression. It wasfound that any error made at the first stage ofexpression was repeated at the second, but thaterrors did not arise de novo in the second stage.The initial stimuli were, of course, single. When achild is reading his perception of the sense of apassage may correct what he has seen, or when hehears that he has said something absurd, he will lookagain and correct himself. This, of course, cannotoccur when pure stimuli of sound or sight are used,though it is not uncommon in ordinary life.

Reversal symptoms may be avoided if the initialstimuli are multiple. For example, ear to writingdoes not reverse if emphasis and rhythm are addedto the sound. The louder the sound, the less likelythat only the dominant ear will be used. Similarly,vision will be accurate if the figures or letters arevery large. It is often seen that some children addkinaesthetic memory to vision so that they canreproduce a design correctly. Irregular eye move-ments are avoided when the left-eyed child is pre-vented from using the eye in a left-right horizontaldirection.

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CROSSED LATERALITY

Treatmeit of Crossed iaterality

Transference of dominance from its natural sideto the cerebral centre on the opposite side can onlyoccur if the first centre is completely destroyed whilethe child is still very young. Similarly, but withmore hesitation, the same may occur if the organconcerned becomes functionless. After the child hasreached the pre-puberty age of 6 to 9 years fullfunction is never regained. Such catastrophes can-not, of course, be reproduced as a form of therapy.Attempts to change the dominance by forciblyrestricting the use of the dominant functioningorgan-this is usually the hand-meet with varyingdegrees of apparent success. Forcible restriction ofthe use of the dominant hand does not stop thecerebral function, though the nervous impulsescannot find expression. As a result the function isinitiated, first from one centre and subsequentlyfrom the other. This state of cerebral turmoil orindecision is shown in clumsy hand movements. Theturmoil spreads and other centres are involved. Forexample, speech ceases to be the expression of onecentre. The resultant stammer is comparable toputting two men on the driving seat of a coach andpair.The degree of success depends upon the fixity of

the original cerebral pattern and upon the intelli-gence of the child. If the inteligence is high, it mayappear that there has been complete success, butthese children always show some irregular domin-ance. Treatment muist be aimed at overcoming thesymptoms which handicap the child. A clue to thishas been given by observing the compensationsdeveloped by inteligent children. The methods usedhave been amplified from experimental findings, andhave proved successful in dealing with these handi-capped children.To prevent incorrect expression of what is heard

it is necessary to avoid the single use of the dominantear. In place of a soft monotone (as of a tiredteacher) a full sound, with rhythm and emphasismust be made. This is easy with reading or thelcture type of lesson, but there are sometimesdifficulties when figures are read either by the childor the teacher. This difficulty has been satisfactorilymet by adding a musical memory. Each figure hasits own musical pitch thus:

S

QJ 0 ~ gn_

The number 9461 would ZX ZZ9 Ithen be read as: 9A` ; 6

This does not involve any musical ability, and canbe used by a child even when reading silently.Reversal is absolutely avoided.The problem of accurate expression of what is

seen is approached differently. Where hand and eyehave opposite dominance, writing can be madeeasier and more regularly formed if the child istaught to turn the book and write obliquely. Thechild with /LR/ should write away from himself, andwith /RL/ towards himself. Reading for thesechildren can also be made easier if the book is heldobliquely. Reading for content must not be hurrieduntil the child has overcome the handicap entirely.These children should not be expected to read aloneproblems written on a blackboard, especially ifnumbers are involved. While the child looks at theboard, the teacher should read the problem usingcorrect emphasis, and the musical notation fornumbers. After a period, the length of which willvary with the type of cerebral irregularity and thechild's intelligence, it will be reasonable for thechild to work alone.When incorrect perceptions have already become

common the child will have difficulty in spelling,a diffulty which increases rather than being over-come. The essential need is to obtain a correctappreciation of the form of the word. This may bedone by considering the word as a design which isto be reproduced and adding kinaesthetic to visualmemory. The word should be written by the teacheron a strip of paper in large (1 to 2 inches) copper-plate letters. The child then traces over these letters,using the whole arm, and keeping the finger tip onthe writing he is following, while the word is pro-nounced in letters or syllables. This is done severaltimes until the child is sure of the word. There isnothing to be gained by hurrying, and making amistake is a backward step. Unless the child iscertain he should return again to the copy. Thisusually results in a noteworthy improvement quitequickly, but it must be remembered that there isprobably a debit balance of bad spelling to be erasedfrom the memory. New words will be larned morequickly than old words which have been fumbled oralways spelt with one persistent error. This methodof learning new words must be used almost in-definitely. If it is neglected the child drops backinto all the old troubles in the course of a fewmonths. The advice that children should write the

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word in the air or on the desk before they do so onpaper does not meet this difficulty. When the childdoes this he is expressing what he has perceived, notcorrecting his perception by the addition ofkinaesthetic sense.When it can be shown that the child has ability

to use both hands he should be trained to use firstof all the hand that brings dominance completely toone or other side. Thus, L L rl L should be taughtto be L L L L and R R rl R should becomeR R R R. Having set the child to develop in thisway, the ability of the other hand should not besuppressed, but encouraged to become a usefulancillary hand. Sometimes a child shows somedegree of ambidexterity, but is so crossed that hecannot be trained into either complete left or com-plete right dominance. He should then be so taughtthat the hand of which is required the highest skillfits best into the pattern of cerebral dominance andproduces minimal symptoms. For example, L L ri Rwill probably turn out best if he be trained tobecome L L R R. Then expression and receptionare balanced. But if the position of the dominantspeech centre is determined one can train the childinto a more secure position; thus L L (L) rl R willdo better as L L (L) L R while L L (R) rl R shouldbe taught to become L L (R) R R. A watch shouldbe kept lest the child shows any symptoms of distressand adjustment made accordingly.

Emotional disturbances will have occurred ifsymptoms have persisted for any length of time.This will respond to general treatment if the under-lying cause is corrected. When the condition is foundin the early stages of schooling (this is the time whendiagnosis should be made) the child must be taughtthe way to compensate for the handicap, but at the

same time the child, his teacher and his parentsshould understand that he is not abnormal in apathological sense, but rather different from many,and with special abilities. When intelligent, olderchildren are discovered who are failing at school orwho have become lazy, a big advance will be madeby explaining to them their handicap, and why theyhave failed. Demonstration to such a child of his realability to reach the right answer, even where he hasfailed (as, for example, in spelling), when he uses themethods suggested is usually followed by a fresh,enthusiastic attack on his work, and he begins totake his proper place among other children.

SummaryCrossed laterality was found among children in a

boarding school. Its prevalence and aetiology areexamined.The natural history and symptomatology are

related to observed educational problems.Experiments are described whose aim has been to

discover the mechanism whereby the symptomsarise.

Effective treatment, which has been suggested byobservation of the natural history of the conditionand of experimental findings, is recorded.

I would acknowledge the kindness of the Lord Godin giving this unique opportunity of studying His work-manship, and His guidance and help as problems havebeen spread before Him in prayer.Thanks are due to the staff (teachers and others) of

the Kuling School of the China Inland Mission for theirwilling cooperation in reporting difficulties and evaluatingthe treatment suggested; the late Mr. F. Mitchell,English Home Director of the China Inland Mission,gave permission for the presentation of this report.

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CROSSED LATERALITY - BMJ