Neurologic approach to specific language disability

NEUROLOGIC APPROACH 17 NEUROLOGIC APPROACH TO SPECIFIC' LANGUAGE DISABILITY* MANUEL R. GOMEZ, M.D.** I shall discuss here the neurophysiologic basis of language disability, making use of information borrowed from classic neurologic sciences. Observations made in the past 100 years and experiments carried out in the past 40 or 50 years have not only failed to answer all of our initial questions on language disability but have brought forward many new ones. Psychologic experiments also have contributed partial solutions and at the same time have widened the research on disorders of language function. That language is a function of the living brain is a well-established fact. It is also well known that the two cerebral hemispheres need an adequate supply of oxygenated blood and that in certain circumstances, when such a supply is impaired, the individual may lose his ability to speak, to understand spoken words, or to read or write, as well as to move parts of his body, to appreciate the position of his limbs in space, to recognize objects placed in one hand, to see on the right or left field of vision, etc. The pathologic examination of the brains of persons who had lost language function has taught us that the center for decoding spoken language is in the posterior part of the left cerebral hemisphere. During early life, this area of the cerebrum is programmed for the function of decoding auditory messages in the form of spoken words. More posteriorly located in the left cerebral hemisphere, there is an area of cerebral cortex that has a very significant function in decoding written messages. In school, between the fifth and 10th years of life, this area of the cerebral cortex is programmed for decoding those written symbols called letters which, properly arranged, form words. This discussion of the neurologic aspects of specific language disabilities will consist of the fellowing parts: ( 1 ) spoken language (verbal decoding and encoding)--acquisition, dissolution, and developmental failure; ( 2 ) written language (script decoding and encoding)--acquisition, alexia, and dyslexia; and ( 3 ) cerebral dominance in relation to language disability. Spoken Language Acquisition--Learning to speak a language requires an adequate hearing organ to transmit electrical impulses via the cochlear nerves and auditory pathways of the brain stem to the auditory cortex. The many impulses received in the cortex need to be sorted out before they can be * Read at the meeting of the Capital Area Branch of the Orton Society, Washington, D.C., May 2, 1970. ** Section of Pediatric Neurology, Mayo Clinic. Associate Professor of Pediatric Neurology, Mayo Graduate School of Medicine (University of Minnesota), Rochester. 18 BULLETIN OF THE ORTON SOCIETY recognized. This is a process of decoding that requires elimination of redundant impulses and selection of those impulses suitable to form associations with other sensory experiences. Attention to sounds is the beginning made by the hearing infant toward decoding in his auditory cortex the millions of impulses transmitted from his ears. A correlation is established between sounds and other simultaneous sensory experiences, chiefly visual and tactile. The infant learns what causes sounds and gradually directs his attention selectively to speech sounds (maternal voice, etc.). He also hears the sounds he himself produces. The redundancy of impulses reaching his auditory cortex requires further elimination and selection. In this manner the auditory cortex is programmed and the infant, correlating voice sounds with nonverbal experiences, begins to understand the meaning of spoken words. In his first 2 years many millions of impulses must be processed in order to provide the units needed to program the developing brain. The child/earns an auditory code that enables him to decode spoken words. He acquires the ability to receive verbal information, a rapid and efficient form of communication. During the same period of about 2 years, his utterings will pass the stages of (motor) speech development: from undifferentiated to differentiated cry; from random production of sounds or babbling to imitation of speech sounds, repetition of sound-complexes or syllables, and echolalia (repetition of words he does not understand); from saying single words with meaning to, finally, forming phrases or short sentences by combining several words. As motor speech develops, the child's utterings progress from demanding words or short phrases to an egocentric soliloquy and, finally, to propositional and socializing language. Dissolution and Developmental Failure of Speech and Language-Anteriorly located in the left cerebral hemisphere--more exactly, in the posterior two thirds of the third frontal convolution--is the motor center for speech. It is well known that lesions in this area cause loss of the ability to encode the necessary impulses which, sent to muscles of the lips, tongue, soft palate, larynx, etc., in an organized fashion will result in speech. The defect caused by such lesions is called apraxia of speech, although some may prefer to call it motor or Broca's aphasia. When caused by failure of development, it is known as developmental apraxia of speech or developmental apraxic dysarthria (sometimes misnamed developmental or congenital aphasia); and this is a fairly common cause of defective speech. In the adult, acquired disorders of the reception of language that result from dissolution of cortical function vary from word-deafness or verbal agnosia, wherein words or sentences are not understood, to a more global kind wherein all auditory messages are meaningless. Said in different words: receptive language disorders can be separated in two general categories--disorders of recognition of phonemes and disorders of recognition of phoneme arrangements. Receptive aphasia has its counterpart in children, which is called developmental word-deafness or receptive language disorder, and is a variety of cortical auditory imperception or central 19 NEUROLOGIC APPROACH deafness that must necessarily produce a severe deficit in the general learning of a child after the age of 1 year. This is because the majority of learning after 1 year of age depends on hearing and understanding spoken language. Developmental word-deafness sometimes is associated with hearing deficit but may occur despite adequate hearing of pure tones. It is frequently familial and is found in boys five times as often as in girls. It is not known whether developmental word-deafness is due to inability of the primary auditory cortex to make proper sleections from the impulses received, or to failure to eliminate redundant impulses, or to lack of connecting pathways for forming associations with other areas of the sensory cortex. The first two hypotheses are adequate to explain a disorder of phoneme recognition, while the latter is more likely to underlie a disorder of recognition of phoneme arrangements. When the child does not understand he pays little or no attention to spoken words and therefore appears to be deaf--or he may indeed be deaf at a cortical level because he is not able to differentiate sounds. "Word-deafness" is, therefore, a good descriptive term for such disorder. Some of these children may develop a vocabulary of their own, comprehensible only to those who have been close to them. Some may be taught to lip-read. Occasionally they also have difficulty in learning to recognize and memorize written words, which constitutes an extremely serious double handicap. Written Language Acquisition--Gibson 1 has explained that reading is "making discriminative responses to graphic symbols" or "decoding graphic symbols to speech." A child who is still too young to read, not knowing the meaning of written symbols, pays little or no attention to letters and written words. Before his third birthday, the average child looks at colorful pictures in children's books, photographs in magazines, and drawings representing persons, animals, or objects. The child's attention to these visual stimuli is maintained as long as impulses from the retina arriving in the visual cortex can be interpreted, or given meaning. This interpretation requires comparison with stored images of previous visual experiences. When associations can be made between pictures on a page and stored visual or non-visual experience, the child can maintain attention to the pictures longer. For instance, he will look at the picture of a cat or other animal, but it is unlikely that he will look at the picture of an ameba. As the child grows older, his interest spreads to visual images representing obiects in a more simplified or stylized form. He is no longer looking at real objects, photographs of them, or even realistic designs, but he is paying attention to and recognizing what amounts to a symbolic representation of the object. If the visual stimulus is a written or printed letter or word or group of words, the eyes of an illiterate child will search for other visual stimuli on that page of the book or out of the book. I Notes will be ~ound on p. 29. ~0 B U L L E T I N OF T H E ORTON SOCIETY By the age of 5 years, most children are able to memorize a few written words, if they have learned to differentiate graphic symbols. T h e r e is good evidence that in this early stage the child recognizes the word by a particular feature which is easy to remember. For instance, the word "look" is recognized by the "oo" (two circles together, resembling two eyes). Depending on the method used to teach reading, the child learns to differentiate letters by design (of the educator) or spontaneously. Discrimination of letters is the basic step for decoding written words to spoken words. Gibson 1 has pointed out that a very young child or even a monkey can be taught to respond to the printed characters YELLOW by selectively pointing to a patch of yellow color, and yet neither the young child nor the monkey is able to decode written words. Experiments made by Gibson and associates 2 suggest that between the ages 4 and 8 years * " . . . what they learn are the features or dimensions of difference which are critical for differentiating letters." We shall see later how the direction of a symbol or "directionality" plays a very important role in learning to read with o u r alphabet because a reversed or mirror-image of some letter is a totally different letter and, therefore, represents a different sound. When a child sees the word "book" and is taught the corresponding spoken word if he has previously learned the word "look" he will associate the symbols 'T' and "b" with their proper sounds. Thus he automatically learns the correspondence between graphemes and phonemes. The process of learning to read is to acquire a written symbol or grapheme for each auditory symbol or phoneme. Each phoneme or speech unit may be represented by one or more letters forming the grapheme. Experiments by Bishop3 demonstrated that adult subjects who are faced with the task of learning a new auditory and written code will do better if the method used requires that they first learn letter-sounds than if they are to learn the entire words without being taught the individual letter-sounds. Furthermore, the subjects in the last group, who did well, had used lettersound correspondences that they themselves had found. Oral reading, or reading aloud, utilizes the motor pathways previously established for speech. Reading can be simply an automatic motor act resembling echolalia (that form of speech consisting of repetition of words without understanding their meaning) or can be a process of decoding written language to receive information, accompanied or not by oral reading. The oral reading of early years may persist in the form of lip movements that one sees in some people even in adulthood, particularly those who have not had much schooling and have not read much or have had difficulty learning to read. Alexia--A patient who has lost his ability to recognize words or letters and yet is able to see and even to write spontaneously is said to have alexia or word-blindness. As pointed out in 1892 by Dejerine, 4 wordblindness accompanies word-deafness in patients with a lesion in the * C o m p a r e W h i t e , this issue. NEUROLOGIC APPROACH 21 supramarginal gyrus of the left cerebral hemisphere. Such patients have a complete receptive agnosia for spoken or written words. If the lesion is more posteriorly situated, the patient's difficulty is restricted to comprehending written language; if the lesion is more anterior, his difficulty is only in understanding spoken language. Agraphia, or inability to write, accompanies alexia when there is a lesion in the angular gyrus of the left cerebral hemisphere. Dejerine also presented evidence indicating that subcortical lesions of the left angular gyrus produce alexia without agraphia. Therefore the left angular gyrus must contain the center for integration of those impulses originating in the visual cortex as a response to seeing written words. The process of decoding written symbols starts in the visual cortex of both cerebral hemispheres and is completed in the left angular gyrus. Impulses from the right visual cortex pass to the left angular gyrus via the commissural fibers in the splenium, or posterior part, of the corpus callosum. When there is a lesion in the left occipital lobe and another lesion in the splenium of the corpus callosum, no impulses from primary visual areas can reach the left angular gyrus and the affected person suffers alexia without agraphia. Although he is unable to read visually, he may be able to recognize letters if he traces them with his finger or if someone holding his finger traces the letters with it. This is because the impulses originating in the parietal cortex which bring kinesthetic information from the tracing finger are sent to the angular gyrus, where decoded impulses of visual-auditory-kinesthetic origin have been encoded and memorized previously. Now, without visually originated impulses, the patient reads with his finger. This was seen in a case reported by Dejerine 4 in 1892, illustrating alexia without agraphia. When an additional stroke damaged the patient's left cerebral hemisphere, precisely in the angular gyrus, he lost the ability to write spontaneously or from dictation. This indicates that stored images of words which he could write but could not read were destroyed by the second lesion. Perhaps it is oversimplifying the facts to propose the existence of a cortical center for reading. But provisionally, one could say that incoming impulses from primary sensory areas of the cerebral cortex--namely the visual, auditory, and kinesthetic--are integrated in the angular gyrus where encoded impulses originate for transmission to the motor area of speech for oral reading and the motor area of the hand for writing. Understanding the meaning of reading material is a higher or more intellectual function of the brain, built on the understanding of spoken language. Dyslexia--At the present time, dyslexia is the most important problem shared by teachers, psychologists, and physicians. Unfortunately, not all members of these professions have agreed on a suitable definition; and indeed there are opposite opinions on the meaning of the word dyslexia. Some go as far as saying that dyslexia is a meaningless term applied to an erroneous concept. Others claim that the term has no definition or is so difficult to define that such a diagnosis is a wastebasket for all children with difficulty in learning. The August 1969 report 5 of a National Ad- 22 BULLETIN OF THE ORTOI~ SOCIETY visory Committee on Dyslexia and Related Reading Disorders, established by the Secretary of HEW, stated that "after an extensive review of the literature and of the opinions of the scientific and professional community, the Committee unanimously concluded that there was no prospect of arriving at a definition of 'dyslexia' which could be accorded general acceptance." It is indeed disappointing that the National Advisory Committee on Dyslexia could not propose even a provisional definition for dyslexia and so reduce the obstacle created by disagreement on such an important matter. The lack of a definition may contribute to its being ignored and neglected by some teachers, psychologists, and physicians. It seems better to take a positive approach, even at the risk of being considered strongly biased. I have accepted the view that dyslexia is a clear-cut entity, a specific constitutional disorder, genetically determined, and distinguishable from other forms of reading disability (as Hinshelwood 6 stated) "by its gravity and by its purity." For an example, a dyslexic boy attending second grade, 8 years and 8 months old, was asked to read the following simple sentences. A boy had a dog. The dog ran into the woods. The boy ran after the dog. 7 In his response, italics indicate wrong words and spaces indicate silence. A dog . . . . . . . . . . . The .... and . . . . . . . . . . . . . . The dog and . . . . . . . . . . . . . . This boy not only is of average intelligence but has normal vision and hearing. He has no abnormal neurologic findings other than the inability to read despite conventional classroom teaching. His normal vision allows him to see the symbols in front of him. His eyes (including retina), optic pathways, and visual cortex are capable of transmitting electrical impulses: he sees the symbols he looks at. One can suspect ( 1 ) that the subject is unable to establish a visual-auditory language link and hence does not memorize the visual representation of each word, or ( 2 ) that the process of decoding impulses sent from the primary visual cortex to the visual-association cortex is impaired so that he fails to decode entire written words, single graphemes, or even individual letters. Visual D e c o d i n g - - A s mentioned earlier, the first step of reading is learning to recognize letters, or graphic symbol differentiation. At the basic level, the child may fail to distinguish letters because he is not able to discriminate them or detect their differences. It is possible that when looking at a symbol, the subject is unable to distinguish it from another symbol that resembles it or is exactly like it except for different directionality. "Directionality" is best understood if one notices that the letters of our alphabet fall in one of five types according to whether they change when oriented in the four possible ways on a NEUROLOGIC 23 APPROACH plane (Fig. 1 ). There are only four letters of the O type w h i c h - - i n their capital forms--constitute no problem in regard to directionality because no possible orientation changes their appearance (Fig. 2). Letters F, G, J, L, P, Q, and R have four possible images according to their orientation (Fig. 3). Of all the directionality confusions, the most common type is the mirror-image. This is to be seen in the confusion of the small letters d and b, The subject whose reading was represented above reads dog for boy or boy for dog, indicating that when he looks at the first letter he mistakes it and, choosing the wrong letter, he guesses the wrong word. He guesses a three-letter word starting with d (dog) instead of b (boy), or vice versa (Fig. 4). This disorder of direction sense can also occur with entire words, as is seen with the words on ( n o ) and was (saw). Letter type Reversed Inverted 180" rotated image i m a g e image 0 0 0 0 B 8 B U N H H N F :1 k :1 A A V V Fig. 1. Letters of five types affected differently by directionality. OO OO I I I I ii XX XX HH HH d Fig. 2. Letters whose capital forms are not affected by directionality. 24 BULLETIN F 0 OF THE ORTON SOCIETY ,tJ JL lr rl 't' II J R.q UU r~ LJ Fig. 3. Letters whose capital forms have four images, according to directionality. Each corresponding lower-case letter except l is equally affected. Mirror reading letters dog Mirror reading words 0 n WaS boy no SOW Fig. 4. Mirror reading of letters and words. Omitting blond bond letters sOon son Transposing S to p there s po t tl~ree letters Fig. 5. Errors of numerality, above; errors of ordinality, below. NEUROLOGIC APPROACH 25 One also sees that knowing the number of letters forming a word gives the subject an additional clue about the word, and he may read it correctly if he recognizes the first letter. When there is unawareness of the numbers of letters in a word (numerality), the subject frequently reads a different word by omission or addition of phonemes (Fig. 5). The many possible arrangements or sequence variation of letters permit innumerable words with only 26 letters of our alphabet. The order of letters (ordinality) establishes a new requirement on the reader. If he is unable to see or to recall the correct sequence of a group of letters in a rapid and automatic fashion, he will not be able to see the word or will read it as a different word or perhaps a non-existent word contrived by transposition of letters (Fig. 5). A written page is consequently a sort of alphabet soup to the child who has not been able to grasp the order of the letters forming each word. It seems reasonable to propose that this is due to an inability of the cerebrum to establish a memory track of a series of decoded visual symbols without losing the proper order. However, an individual may utilize an auditory memory track to bring the proper word if he is able to associate or correlate each successive visual symbol with a corresponding auditory image, translating the graphemes into phonemes and assembling the phonemes into words. In doing this, he is using phonics. Vision SDYmboI differentiation \ irectionality of symbols Perception "~~,,,~sUmerality of symbols \ equence of symbols Recall \ Association / y~~Tactile pathway Auditor Kinestheticpathway pathway - Fig. 6. Components of visual process of reading, and relationship of visual, auditory, tactile, and kinesthetic input for reading. 26 BULLETIN OF THE ORTON SOCIETY If the individual has such visual-auditory disconnection that he is totally unable to name letters and "sound them out" when he looks at them, certain alternative inputs and connections may serve his need. He may perhaps bring out each phoneme by tracing letters with his fingers to enable himself to say them. He can trace them on the paper as did the patient with alexia described by Dejerine, 4 or in the air as many of us have done when trying to recall verbally the spelling of a word. The need to trace before verbal spelling, though one can easily spell simultaneously with writing, indicates that there are auditory-kinesthetic connections supplementing auditory-visual links. Figure 6 illustrates the relationship of visual, kinesthetic, and auditory input and also the components of the visual decoding process for reading. Auditory Decoding--Like visual decoding, the auditory decoding process consists of several components. The first is auditory discrimination of sounds at the cortical level--that is, decoding of impulses received by the ears and transmitted to the cortex, a skill which must be achieved before spoken language can be mastered. Prior to learning the visual representation of phonemes as graphemes, it is necessary to distinguish among the phonemes, which may be approximate in their physical characteristics. Making phoneme selection more difficult, there are certain phonemes (for instance, the letter i in "wind") which when transferred to the auditory code require a choice among several possibilities (i as in mind, i as in sin). The process of decoding again requires a selection of one and rejection of other possibilities. This selection requires that the phoneme alternatives be compared with the graphemes seen in context, or with the auditory memory of the phonemes into which the contextual graphemes have been converted. The reader sometimes uses auditory reinforcement by reading aloud and even repeating a syllable several times until, after matching the known phonemes with the possible phonemic translations of an unknown grapheme, the appropriate translation can be selected and the rest rejected. From the earlier remarks on ordinality (or phoneme sequence), one can see how memorization of sequences of phonemes or graphemes is so important in learning to read. This ability has been tested with recall of nonsense syllables. Immediate auditory memory is required for retention of the recognized phonemes of an unrecognized word until all graphemes have been decoded into phonemes. Failure of this playback of phonemes in their proper arrangement will interfere with the auditory decoding of entire written words (unless the reader can memorize them visually) and will make correct spelling while writing from dictation cumbersome if not impossible. NEUROLOGIC APPROACH 27 Cerebral Dominance and Language Disability A close relationship between left-handedness or crossed dominance (eye, hand, foot) and developmental language disorders cannot be supported with the available evidence. Malmquist, 8 Spitzer and co-workers, 9 and Belmont and Birch 10 have shown that mixed lateral preference is not more common in individuals with reading disability than in normal controis. Naidoo 11 studied a group of 418 randomly selected children aged 4 years 9 months to 5 years 11 months with a battery of 10 handedness tests. She then selected 20 of the 360 right-handed and 20 of the 38 lefthanded children to compare them with the 20 children who had poorly established dominance. The subjects were matched with regard to age, sex, and type of school. All 60 children were carefully studied with regard to birth history, familial left-handedness, rate of speech development, and intelligence-test scores. The children with poorly established dominance were, as a group, significantly inferior to the other two groups in verbal intelligence-test scores and frequently had a history of slow speech development and of complications at birth. The incidence of left-handedness in the family was the same as in the left-handed group. Flescher 12 designed an experiment to test 150 children for their ability to decipher letters and words rotated in different planes. Fifty children were left-eyed and right-handed; 50 were right-eyed and righthanded; 50 were left-eyed and left-handed. None of the groups showed superiority over another in ability to read rotated scripts. Rutter 1~ has studied the total school population of the Isle of Wight by means of group tests. Children who scored badly in reading accuracy or comprehension were given Wechsler intelligence tests and examined for handedness, footedness, and eyedness. When compared with a control group of 147 children, the group of 86 with reading retardation did not have a significantly higher incidence of left-handedness, footedness, or eyedness or discrepancy in hand-foot dominance. The proponents of the idea that mixed eye-hand dominance or crossed dominance is responsible for disorders of language function and, in particular, of reading, writing and spelling, should first demonstrate that the two phenomena are found in association and second prove that a relation of cause and effect exists between them. It seems unlikely that eye dominance is in any way related to reading, writing, or spelling disorders. There is, undoubtedly, hemispheric dominance or asymmetry of function for both language and spatial gnosis. So far as language is concerned, the left cerebral hemisphere is dominant in 99 % of right-handed persons and in about 70% of left-handed persons, This knowledge is derived from experience with adults who have suffered cerebral insults resulting in aphasia or have received intracarotid injections of sodium amytal. The left cerebral hemisphere also is dominant in the motor act of constructing or copying geometric models. Lesions in this-hemisphere produce constructive disorders due to disorgnaizations of the motor act (praxis), which 28 BULLETIN OF THE ORTON SOCIETY called constructional apraxia. What about the right cerebral hemisphere? Many believe it is dominant in the function of spatial appreciation - - t h a t is, awareness of spatial relations. According to Hecaen, 1. lesions in the posterior part of the right cerebral hemisphere produce neglect of the left part of the model being copied and of the left part of space. There is also diagonal orientation of drawings, inability to give proper perspective in drawings of three-dimensional objects, and failure to recognize different parts of complex two-dimensional drawings. According to Hecaen, x4 disorders involving topographic relationships (inability to orient oneself on a given plane, on a geographic map, on a drawing of a maze~ are related principally to parieto-oecipital lesions located mainly in the right hemisphere. Among 40 cases in which he observed this disorder, the lesion was found on the right side in 29, on the left in 8 (three patients were left-handed~, and bilaterally in 3. In few words, when model-copying is disturbed by cerebral lesions, rightsided lesions are manifested by disproportion and inaccurate alignment of the constituent part of the figure while left-sided lesions are manifested by simplification in the copy. 15 In drawings by children with language disability, it is not unusual to find distortions, particularly of geometric figures such as those in the Bender T e s t - - a phenomenon that psychologists attribute to visual-perceptual, visual-motor, or perceptual-motor difficulty. Fundamental to producing a geometric figure is the process of vision with perception of relations, proportions and angles of lines, and elimination of unnecessary details. But if the process fails between visual perception and manual execution, a geometric figure may be recognized and even described by an individual who is unable to copy it with accuracy. Drawing is a form of praxis requiring that impulses sent from the central nervous system to hand muscles be properly arranged in time and selectively distributed through the motor units involved. This motor act is possible if the figure to be copied has been visually decoded without losing its elementary components in the process of selection and elimination of electrical impulses sent from the visual to the parietal cortex and, finally, if the connections between visual and motor centers permit transfer from the visual to the motor area where the skillful movements are encoded. Disorders of praxis may or may not be associated with disorders of language. It is obvious that, in such psychologic tests as the Wechsler Intelligence Scale for Children, the performance part is heavily loaded with tasks of this type and yet we cannot say that results obtained from administering the WISC to children with learning disorders will allow the examiner to identify a selective involvement of only one side of the brain. The association of disorders of praxis and disorders of other high cerebral functions, including language function with poorly established hand dominance, is not unusual. Possibly they are results of failure of a sensory decoding process. It is accepted that kinesthetic and tactile stimuli from joints, muscles, skin, and vestibular organs integrated with visual and auditory experiences are necessary to establish patterns of motor beare NEUROLOGIC APPBOACH 29 havior. Such patterns include hand dominance or preference. T h e failure or delay in the establishment of hand dominance could be looked at as a disorder of sensory processing or as a failure of the motor encoding. Disorders of spoken and written language, whether acquired or congenital, represent failure of the decoding or encoding process. In this paper the reading process has been analyzed into elementary components which may be found to be at fault in the individuals failing to learn to read. The relationship between specific language disorders and h a n d and foot dominance has been briefly reviewed. REFERENCES 1. Gibson EJ: Learning to read. Science, 148: 1066-1072, 1965 2. Gibson EJ, Gibson JJ, Pick AD, et ah A developmental study of the discrimination of letter-like forms. J Comp Physiol Psychol 55:897-906, 1962 3. Bishop CH: Transfer effects of word and letter training in reading. J Verbal Learning Verbal Behavior 3:215-221, 1964 4. Dejerine MJ: Diffrrentes varirtrs de crcit6 verbale. C R Soc Biol (Paris) 44:61-90, 1892 5. Reading Disorders in the United States: report of the Secretary's (HEW) National Advisory Committee on Dyslexia and Related Reading Disorders. Public Health Service, August, 1969. 6. Hinshelwood J: Congenital Word-Blindness. London, H. K. Lewis & Co., Ltd., 1917 7. Gray WS: Standardized Oral Reading Paragraphs (Gray Oral Reading Paragraphs Test). Indianapolis, Bobbs-Merrill Company, Inc., n.d. 8. Malmquist E: Factors Related to Reading Disabilities in the First Grade of the Elementary School. Stockholm, Almqvist & Wiksells International Booksellers, 1958 9. Spitzer RL, Rabkin R, Kramer Y: The relationship between "mixed dominance" and reading disabilities. J Pediat 54:76-80, 1959 10. Belmont L, Birch HG: Lateral dominance, lateral awareness, and reading disability. Child Develop 36: 57-71, 1965 11. Naidoo S: Cited by Zangwill OL: Dyslexia in relation to cerebral dominance. In Reading Disability: Progress and Research Needs in Dyslexia. Edited by J Money. Baltimore, The Johns Hopkins Press, 1962, p 110 12. Flescher I: Ocular-manual laterality and perceptual rotation of literal symbols. Genet Psychol Monogr 66: 3-48, 1962 13. Rutter M: The concept of dyslexia. Clin Develop Med No 33, 1969, pp 129-139 14. Hecaen H: Aphasic, apraxic and agnosic syndromes in right and left hemisphere lesions. In Handbook o[ Clinical Neurology. Vol. 4. Edited by PJ Vinken, GW Bruyn. Amsterdam, North-Holland Publishing Co., 1969, pp 291-311 15. Warrington EK, James M, Kinsbourne K: Drawing disability in relation to laterality of cerebral lesion. Brain 89: 53-82, 1966