Pediatric Ophthalmology
Edited by P. F. Gallin
Thieme Medical Publishers, Inc.
New York ©2000
6
Learning Disabilities
I felt a cleavage in my head
As if my brain had split;
I tried to match it, seam by seam,
But could not make them fit.
The thought behind I strove to join
Unto the thought before,
But sequence ravelled out of reach,
Like balls upon the floor.
Emily Dickinson
We have all been intrigued by stories of great men and women throughout history who have overcome learning disabilities(LDs). Albert Einstein, Edgar Allen Poe, George Bernard Shaw, and Salvador Dali were expelled from school. Abe Lincoln, Thomas Edison, and Henry Ford were assumed to have limited promise by their teachers. What is the nature of this problem of the mind that produces individuals who may present at once as brilliant and quite the opposite? This chapter is intended to provide a broad overview of LDs, from both a conceptual and an empirical vantage point. The emergence of this field of inquiry as well as issues of definition, classification, and prevalence are considered. With regard to etiology, it is assumed that LDs are either the direct or indirect result of central nervous system dysfunction. Theory and data specifically pertaining to the neuropsychological underpinnings of these syndromes are briefly considered. The process of diagnosis is described from neurological, psychological, and educational perspectives. Interventions and treatments are described, including educational remediation, medication, and psychotherapy.
The ophthalmologist is often the first professional consulted when a child is having difficulty learning, especially when reading is involved. The physician’s task is to determine whether organic visual pathology is causing the learning problem. Can the patient see the target? This first visual arc is the domain of the ophthalmologist. The second arc involves the processing of visual information. This is the province of the LD specialists. The examining physician must deal with the thorny interaction between these domains when a child has no apparent visual pathology but is unable to correctly interpret the stimuli because of processing problems. The position of the American Academy of Pediatrics and Ophthalmology with regard to this interaction is unambiguous. For your convenience it has been reproduced at the end of this chapter (Appendix 6-1).
Problem of Definition
Although the problem of bright children who are unable to read was described in the medical literature a century ago,1 attempts at precise definition have been relatively recent. Diagnosis is still primarily dependent upon psychometric assessment of significant discrepancy between academic performance or achievement in one or more aspects of learning and general intelligence. The disparity in early conceptualizations reflected our lack of understanding of the learning process generally as well as the factors interfering with it. Along with the phenomenological description and differentiation of the concept, thorny issues include the theoretical, clinical, and even legal implications embedded in definitions of LDs, all of which guide our work with children. The practical significance of defining who is learning disabled is highlighted by the fact that federal legislation requires that children and adolescents with specific learning disorders be identified, evaluated, and provided with appropriate school services and academic provisions. Furthermore, the designation of those children eligible for specific educational programs impacts upon the selection of those schools receiving special funding. Currently, although definitions continue to reflect theoretical biases, the growing body of research pertaining to underlying deficits is leading to greater clarity and shared criteria for inclusion. This holds the promise of providing a common diagnostic reference point from which research populations of learning disabled children may be more accurately defined.
It became clear that a stable definition, acceptable to an interdisciplinary constituency, was needed. In response to the definitional confusion, The National Joint Committee for Learning Disabilities (NJCLD) proposed a comprehensive and research-based definition of learning disabilites. Their definition reads as follows:
Learning disabilities is a general term that refers to a heterogeneous group of disorders manifested by significant difficulties in the acquisition and use of listening, speaking, reading, writing, reasoning, or mathematical abilities. These disorders are intrinsic to the individual, presumed to be due to central nervous system dysfunction, and ma occur across the life span. Problems in self-regulatory behaviors, social perception and social interaction may exist with learning disabilities but do not in themselves constitute a learning disability. Although learning disabilities may occur concomitantly with other handicapping conditions (for example, sensory impairment, mental retardation [MR], serious emotional disturbance [ED], or with extrinsic influences (such as cultural differences, insufficient or inappropriate instruction), they are not the result of the conditions or influences.2
Researchers found this vague and unspecific definition difficult to operationalize. The Association for Adults and Children with Learning Disabilities (ACLD) refined this definition, differentiating several characteristics of learning difficulty. This condition occurs in children who are typically of average or above average intelligence and is manifest in significant discrepancy between general level of intellectual functioning (or aptitude) and performance (or achievement) in one or more specific areas of learning and/or cognitive ability. LD may be expressed in either significant delay in acquisition or difficulty in mastering one or more areas of learning. The criteria for diagnosis are both clinical and statistical. LDs exist on a continuum varying from mild to severe. In addition to specific academic skills, other areas of learning that may be involved include organization, impulse control, attention, and coordination. The ACLD reiterates that LDs are generally believed to be neurologically based, with a genetic component. They are not due to intellectual inadequacy, socioeconomic disadvantage, or poor teaching. Over the course of development, LDs can affect self-esteem, education, vocation, socialization, and daily living activities. Three mandates were identified by this committee for presentation to Congress: (1) that prevalence and demographic studies of learning disabilities should be accurately undertaken, (2) that the literature on cause, diagnosis, treatment, and prevention be reviewed, and (3) that suggestions for legislation and administrative action be prioritized. Failure to reach agreement on definition and diagnostic criteria has been a crucial factor inhibiting research efforts.3
The Diagnostic and Statistical Manual 4 (DSM-IV) describes LDs as specific developmental disorders, distinguished by inadequate growth in isolated academic skill areas, such as reading, writing, and math, as well as in the underlying cognitive areas of language, speech, or motor skills. Diagnosis is based upon comparison of standardized achievement tests with tests of general intelligence, both verbal and nonverbal (visual-motor and spatial). The LD is inferred from patterns of performance on a standardized test of that academic area falling significantly below the level expected considering the child’s education and intelligence as measured by a standardized IQ test. LD is diagnosed only when the disorder interferes with school achievement or activities of daily living. Skills vulnerable to specific developmental disorders include arithmetic, expressive writing, reading, expressive and receptive language, articulation, and coordination.
Although precise definition of LDs is still debated, enormous progress has been made in the understanding of the etiological and neuropsychological nature of the many syndromes included under the LD umbrella. As our understanding continues to deepen, it is likely that the universal relevance of this knowledge will be increasingly valuable.
Historical Background
In the 5th century B.C., Hippocrates speculated that language and thought as well as personality were products of the brain. Common knowledge of the time suggested that physical properties such as heat and moisture influenced mental processes such as reasoning. The antecedents of the LD field lie in the history of both educational practice and scientific research. Early definitions were inexact and frequently confusing, reflecting the lack of understanding of the learning process and the factors that interfere with it. It was not until the late 19th century that direct evidence became available confirming Hippocrates’ notion, at least with regard to language.
Driven by their interest in the powerful relationship between brain and behavior, scientists including Wernicke and Broca studied acquired brain pathology, providing enduring observations central to later conceptualizations of the neurological substrate of LD. Their clinical and autopsy studies of adults after strokes or other brain injuries allowed them to localize specific cognitive abilities, such as language and spatial ability, to specific parts of the brain. They noted that aphasia resulted from injury to the left hemisphere, that language was localized in the second frontal convolution of the left hemisphere, and that this phenomenon was absolute in right-handed subjects.5 These observations and the complex relationship between handedness and lateralized function continue to concern current investigators.
Dyslexia was the first specific LD described in the medical literature. In 1878, a German physician, Kussmaul, described a man of normal intelligence and perceptual ability who was unable to read. Kussmaul called this condition “congenital word blindness.” The term dyslexia was coined 9 years later, and in the first years of the 20th century a series of clinical reports by other researchers appeared supporting the existence of a congenital syndrome characterized bya developmental inability to read.6,7
In the 1920s and 1930s, Orton advanced the notion that reading disabilities were independent of general intelligence. He differentiated acquired disorders from dyslexia, in which the impairment in reading sklls is assumed to be neurologically based and present at birth. He worked inferentially from acquired reading disabilities in adults unimpaired prior to brain injury. Orton speculated that reading problems in children with symptomatology similar to his adult subjects might be caused by a common neurological condition.6 He popularized the idea that a delay or failure in the establishment of lateral dominance was causally central (i.e., lag in the left hemispheric central language processes). In the current literature, it is noteworthy that the elucidation of developmental disorders in childhood appears to illuminate the mechanisms of adult brain function more effectively than does the earlier tradition of extrapolation to the nature of the child from the analysis of acquired disorders in adults.
The complexity of developmental learning difficulties was powerfully highlighted by Gerstmann’s 1940 description of an adult syndrome,5 which included disorders in calculation. Gerstmann assumed interdependence among a tetrad of symptoms including dyscalculia, spelling difficulty, directional confusion, and difficulty with finger recognition. He believed this condition evolved from an acquired brain dysfunction involving the left parietal lobe. Studies of children presenting with this syndrome appeared in the literature shortly thereafter. In the reports, left-handedness was prevalent, as was family history of academic difficulty. Organic brain dysfunction was assumed to be the result of some acquired traumatic mechanism. The absence of hard evidence of brain injury in LD children as well as concern about the negative impact of labeling children as “brain injured” led researchers to drop this terminology while retaining the assumption of underlying neurological cause.
This early phase in the history of LD was thus characterized by studies of the relationship between brain and behavior and resulted in several theoretical formulations as to the essence and etiology of learning problems. From the 1940s until the mid-1960s, professional interest in LD was focused primarily on pragmatic issues of intervention rather than on refining our understanding of the essential nature of LD. This period was marked by the emergence of a variety of remedial systems for treating LDs.
Since the mid-1960s, the LD field has expanded rapidly. New remedial techniques, programs, and services have proliferated, and increasing numbers of professionals from several disciplines are involved. The term learning disability was introduced in 1963 to encompass these conditions, their manifestations, and assumed etiology. To enjoin educators to help those individuals manifesting selective academic underachievement, LD was presented as “special needs category” at a national conference addressing the provision of services by the public schools for reading- and language-impaired children. The resulting U.S. Public Law 94-142 made three pivotal assumptions that are shared by current conceptualizations as well: (1) the learning problem is specific to an articulated academic domain, (2) there is psychometric demonstration that achievement is not commensurate with intellectual ability, and (3) exclusionary criteria are met, demonstrating that the learning problem is not the result of a concomitant condition.
Epidemiology
Estimates of the prevalence of learning disabilities vary considerably across studies in the literature. In part, this is an artifact of research shortcomings, in that investigators do not always agree on criteria for identifying LD subjects. In addition, epidemiological studies are more complicated for behavioral syndromes than for physical syndromes, where classification is based on all-or-none criteria. Within the United States between 7 and 15% of the general school population is assumed to fall more than one standard deviation below average in nationally normed reading or math scores. The literature estimates that between 2½ and 5% of the school-aged population is identified as learning disabled. Although LD emerges as a diverse and variable phenomenon, at least one half of these children are dyslexic.8–10
As for gender breakdown, it is commonly asssumed that LD affects far more male than female children. The most frequently reported 3:1 male:female ratio is consistent with ratios for other special education classifications. Recent data suggest that these data be reconsidered to reflect variation in the ratios of difference from one dysfunction to another. Boys appear to outnumber girls in populations of children with receptive and expressive language problems as well as reading disorders. The more disruptive behavior of male pupils in classrooms may lead to their overreferral and subsequent more frequent diagnosis. These gender differences have led to the postulation of sex-linked mechanisms of genetic transmission of LD, although this theory is as yet unsubstantiated by hard data.11 Curiously, family reports indicate an equal number of male and female learning disabled individuals.6
Within learning disabled populations, estimates of those who also have attentional deficits vary widely, ranging from one third to three quarters struggling with concomitant learning and attentional difficulties. Boys significantly outnumber girls with attention deficit disorder (ADD). At present, interest in learning and attentional problems is largely a phenomenon of the developed world, where academic success is valued, and unpredictable or unexplained failure is of great concern to parents, educators, and the child.
Etiology: Theory and Data
The data strongly support the assertion that many learning problems are the result of neurodevelopmental aberrations within the central nervous system, which interfere selectively with cognitive and academic functioning. Underlying this belief is the assumption that there is a lawful relationship between normal brain functioning and specific patterns of behavior. Indeed, neuropsychological assessment has consistently and systematically differentiated among children heterogeneously classified as learning disabled, relating hemisphere of impairment to specific nature of dysfunction.7 Theoreticians and clinicians from a variety of perspectives have considered the causes of LDs. An extensive body of literature exists, focusing on underlying causal agents ranging from genetic factors to nutrition. Much of the literature suffers from a common problem. There are many unidimensional conceptualizations, narrowly focused on a circumscribed view of LD. Currently, those at the forefront of the LD field are working toward broader formulations that attempt to subsume and integrate the patchwork of extant data and theory.10,12 At present, what may be described as a developmental-neuropsychological model appears to encompass and integrate much of the data in terms of explanatory and predictive power. Simply put, although the source of the problem in a specific LD is assumed to be embedded in the central nervous system (CNS), it is difficult to establish a direct link between the neurological impairment and academic difficulty. In addition, these correlational data explain little about the influences producing idiosyncratic brain function or what mediates between actual brain function and observable learning behavior. These relationships between brain and behavior are conceptually enhanced and logically strengthened by the inclusion of “intrinsic” genetic and “extrinsic” environmental factors as well as the imposition of those cognitive processing capacities that mediate between brain neurochemistry, or neurophysiology, and a child’s ability to learn. The psychological processing of mental data, crucial to learning, suggests a more coherent group of capacities that are both essential to adequate learning experience and vulnerable to dysfunction. This model implies a complex, interactional approach to the investigation of LDs. Understanding of the neuropsychological underpinnings of LDs must always include examination of the genetic and/or environmental factors that may lead to brain malformation, dysfunction, or delayed development. These conditions in turn may contribute to deficits in the processing of mental data, which may ultimately be expressed in a specific LD. A brief description of these etiological factors that may interact in children with LDs will demonstrate the complexity of this group of syndromes and is likely to raise more questions than are answered!
The notion that some form of genetic transmission is involved in LDs is suggested by the finding that they seem to run in families. The literature estimates that up to 40% of children and adolesents with LD may have inherited this condition. The evidence includes family histories, often noting the presence of parents or siblings with similar difficulties. Compared to the general population, researchers have demonstrated statistically greater co-occurrence of LD in monozygotic and dyzygotic twins, with greater concordance in monozygotic pairs (71%) than their dyzygotic counterparts (49%). In addition, the likelihood that LDs persist over a lifetime supports the hypothesis that there is a genetic component. Comorbidity with other disorders has also stimulated investigation of the heritability of LD. For example, a linkage was postulated and confirmed among dyslexia, left-handedness, and autoimmune and allergic disorders, based on a theory of prenatal testosterone exposure in utero.3 The authors warned, however, that it would be premature to assume that testosterone is a central etiological substrate of either dyslexia or left-handedness. The genetic basis of handedness has also been associated with LD. Although equivocal, the literature suggests a greater prevalence of left-or mixed-handedness among LD individuals than among their non-LD peers. The specific mechanism of inheritance remains a matter of speculation.
Both pre- and perinatal stress factors may set the stage for injury to or abnormalities in the maturation of the brain, subsequently expressed in the form of LDs. Many variables have been investigated to varying degrees. Autopsy reports have indicated both asymmetries in the planum temporale area and anomolies in the convolutional patterns of the parietal lobes of dyslexics. These data provided evidence for the “faulty wiring” concept of LD. Sociocultural factors, extrinsic to the LD child, can also have a negative effect on the developing brain. These may include poor maternal nutrition, inadequate prenatal care, metabolic or toxic factors, infections, and stress. There is evidence that the presence of pregnancy and birth complications (particularly anoxic episodes) as well as prematurity and low birth weight are statistically correlated with later speech and/or reading difficulty. Recent studies of substance abuse during pregnancy are distressing. The data confirm increased incidence of hyperactivity, distractability, and irritability in these babies, and of LD as they enter school. The investigators stress that the occurrence of such complications is neither a necessary nor a sufficient explanation for the existence of an LD.
Two contrasting explanatory models have been proposed to account for the neurodevelopmental aspects of learning problems. One focuses on cerebrally based, neuropsychological deficit that may take the form of faulty hemispheric organization, brain asymmetry, or abnormal development of neural cells and transmitters. The second is a neurodevelopmental delay model, which is based on several explanations, including a lag in the establishment of cerebral dominance or laterality.
The deficit hypothesis, an outgrowth of the medical disease model, assumes that the academic dysfunction is the result of a CNS deficit intrinsic to the child. A number of deficit-based explanations of LD have garnered empirical support. A major difficulty is the number of possible deficits that may be involved, including encoding, decoding, attention, memory, sequencing, and so on. Many studies have speculated on the possible locus of neurological dysfunction, but none has received unequivocal support. For example, studies using computed tomography (CT) scans have posited reversed asymmetry in LD groups (i.e., right rather than left hemisphere language). A limited number of autopsy studies have attested to structural abnormalities in the cerebral hemispheres of individuals with severe LD. The data suggested cortical disorganization and clusters of displaced neurons. Comparative studies of normal brains are necessary to draw conclusions as to the generalizability of these findings. Several researchers have found LD to be associated with significant irregularities in electroencephalographic protocols (EEGs) when compared to normal children. These differences are difficult to interpret because of variations in populations sampled, experimental methodology, and statistical analysis.10
Delay hypotheses invoke the concept of a maturational lag in the neurological development of left-hemisphere specialization. It is assumed that delayed growth of cerebral centers results in this neurological immaturity. The defining characteristic of LD children is believed to be a less mature level of patterning in perceptual, motor, or other mental activity. Neither structure nor function is viewed as defective. Maturation is expected to continue, if slowly, and may even accelerate after puberty. This approach thus implies that some of these children will eventually catch up with their peers, acquiring the neural circuitry necessary for learn normally. In fact, there is little convincing evidence of systematic changes in brain lateralization with age.14 Proponents of the delay model have had to modify this line of reasoning, positing that learning difficulties may persist into adolesence and adulthood because the learning experience and attitude of the child are negatively affected.
Like the nature versus nurture controversy, the issue of deficit versus delay may most constructively be conceptualized interactionally rather than in opposition, as both factors may powerfully influence the development of LDs. Although a deficit or brain trauma in a child can result in developmental delay, a significant maturational delay could result in neurological organization that remains deviant.13
Clinical Presentation
LDs may present singly or in combination with other LDs. Both verbal and nonverbal functions are essential to school success, and both areas are vulnerable to developmental deficiency with fairly predictable dysfunctional manifestations. This section describes the clinical phenomenology likely to be encountered in children with specific LDs.
Differential Diagnosis
As noted in relation to the exclusionary criteria for defining LD, LD may occur concomitantly with other handicapping conditions. However, it must not be caused by or the result of these conditions or influences. Factors that must be considered for etiological elimination include mental retardation, physical disability (cerebral palsy), brain damage from trauma or infection, sensory impairments (auditory or visual), environmental deprivation (including inadequate instruction), emotional disturbances, and medication effects.
Classification
Two trends in the classification of LD syndromes prevail in the current literature, one focusing on the cognitive process underlying the dysfunction and the second describing their symptomatic manifestation. In the first, LDs are conceptualized by the cognitive processes centrally involved. Levine, for example, a foremost current researcher and clinician, differentiates among difficulties in the processes of attention, mental processing, and output.12 More frequently, however, the specific academic subject area affected defines the diagnostic category or subtype of LD. Researchers concur that failure to differentiate among the various subtypes of LDs can lead to false conclusions or predictions as to patterns of performance. For example, although it has been found that reading disabled children have problems with processing certain aspects of syntax, those with mathematically based disorders do not.7 Both the clinical-inferential and process-based research models have yielded important contributions. Both neuropsychological and intervention studies are central to the validation of LD subtypes. For the purposes of the present discussion, the academic area affected comprises the diagnostic category.
Verbally Based Learning Disabilities
Language Disorders
Children with developmental or acquired language disorders are handicapped in comprehending and/or producing language from early childhood. A myriad of factors are involved in spoken and written language. These include the ability to retrieve words from short-and long-term memory, the organization of these words in keeping with the rules of syntax and grammar, the articulation of a sequence of ideas, and the execution of the complex motor act of speech.12 In school settings, verbal and written language are of paramount importance to success. Beyond their increasing centrality in academic work, these skills are essential for self-monitoring, social interaction, and demonstrating competence in the outside world.
Both expressive and receptive features of a child’s communication skills may be impaired. The linguistic aspects of expressive language vulnerable to disorder vary depending upon the severity of the disorder and the age of the child. They may include voice quality and resonance (i.e., monotonous intonation) as well as lack of fluency and/or poor articulation. The child may have problems manipulating and expressing linguistic symbols. The development of a working vocabulary and the internalization of syntax facilitate meaningful communication. Word finding problems and difficulty with narrative organization are common expressive language deficits. In addition, there maybe difficulty in the composition of written text evidenced by grammar or punctuation errors or poor paragraph construction.
Receptive language skills include the capacities involved in understanding words, sentences, or specific categories of words or statements (i.e., spatial terms or subjunctive formulations). These abilities draw upon interpretation of auditory stimuli and the understanding of spoken language and/or verbal symbols (verbal dyspraxia). The capacity to decode language enhances a child’s mastery of his or her environment. Because the development of expressive language in childhood is inextricably interwoven with the acquisition of receptive skills, a pure receptive language disorder is virtually never seen.4 In keeping with the notion of delayed or deficient hemispheric lateralization, there is neuroimaging and EEG evidence that suggests that LD expressed in processing receptive language is localized in the left hemisphere.
Reading Disabilities (Dyslexia, or Word Blindness)
Dyslexia is defined as the inability to read at a level appropriate to one’s general intelligence. There is great variability in the extent to which reading disorders may interfere with functioning. Their presence is inferred from a discrepancy between one’s IQ score and reading performance. It is suggested that data from more than one context be compiled to substantiate and validate this diagnosis (i.e., from school and home reports). There are numerous patterns of difficulties in reading that have led to the differentiation of several types of dyslexias in the current literature. The symptoms of dyslexia often include lateness in acquisition of reading skills. Reading may be slow and halting, with a lack of fluidity in silent or oral reading. Any combination of several processes may be implicated in dyslexia, including difficulty with semantic decoding, phoneme segmentation and recombination, and comprehension. Both visual processing and visual memory may be involved. For example, letter reversals are common, including confusion in the perception of b and d, p and q, and E and 3.
Spelling Disabilities (Dysorthographia)
Spelling problems are typically part of a broader developmental dysfunction and can result from a variety of deficits. Accurate spelling involves the integration of visual memory, sequencing, and retention. In addition, sound-symbol or phoneme-grapheme correspondences or phonics must be understood. Children may struggle to break words into their component sounds (segmentation) and put these components together (blending). Spelling is vulnerable to problems in visual recall as well, reflected in errors involving the substitution of words that sound the same, although they are spelled and written differently (e.g., grate in place of great).
Nonverbal Learning Disabilities
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