LEARNING DISABILITIES

Definition of Learning Disabilities

Despite federal regulations, the definition of learning disabilities is controversial. The U.S. government defines a specific learning disability as a disorder in one or more of the basic psychological processes involved in understanding or use of spoken or written language, which may be manifest as an inability to listen, think, speak, read, write, spell, or do mathematic calculations. While the definition could include the conditions of perceptual handicaps, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia, it is not applicable to students whose learning problems are the result of visual, hearing, or motor handicaps, mental retardation, emotional disturbance, or environmental/cultural disadvantage. The major premise is that a significant discrepancy exists between the child's potential and her actual level of academic or language skills.

Each state, however, may determine cutoffs for discrepancies or definitions of processing disorders, leading to variability among states and even differences among districts within a given state. The definition and diagnosis of an LD vary, depending on whether the purpose is to qualify for services or to clinically identify the reason for a child's poor academic performance. In the former, measurement of intelligence and levels of achievement is employed; in the latter, administration of IQ and achievement is extended to include evaluation of attention, memory, and neuropsychological function. Moreover, the age of identification varies, depending on the type of LD; some may not be apparent early because academic skills in areas affected by the LD have not yet been challenged.

The psychiatric definition of LDs (as found in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders: DSM-IV) differs considerably from both federal and state classification systems, adding further to the ambiguity. Learning disabilities are presumed to be due to central nervous system dysfunction, and occur across the lifespan. They reportedly occur more in males, although research in the late 1990s by Sally Shaywitz has disputed this contention.

The Discrepancy Issue

The "discrepancy issue" has been established as the primary criterion for identifying children with LDs. Unfortunately, discrepancy formulae are controversial, potentially inaccurate, and inappropriate for detecting cognitive deficits. There are three types of discrepancy formulae.

With an aptitude-achievement discrepancy, a disparity exists between a child's intellectual ability (as measured by an intelligence test) and his actual level of academic achievement (measured by an achievement test). Certain LDs (e.g., a short-term memory problem or central processing dysfunction), however, may also affect a child's performance on IQ tests, thereby reducing the discrepancy between aptitude and achievement. This discrepancy model is useful from third grade onward, and certain disabilities (such as fine motor dyspraxia, retrieval memory dys-function, and organization problems) often are not detected. Children with the most severe LDs frequently have the smallest discrepancy.

An intracognitive discrepancy (a disturbance in basic psychologic processes) occurs in children who have a specific type of cognitive dysfunction such as a deficit in auditory processing, short-term memory, or visual processing. This type of LD is difficult to operationalize, but is useful in identifying preschool and primary-age children who have learning problems.

An intra-achievement discrepancy reflects divergence or inconsistency in educational achievement performances. This could occur between academic areas (such as reading versus mathematics) or within an academic area (such as a marked difference between reading decoding and reading comprehension).

Regression models, which attempt to correct the problems inherent in discrepancy comparisons, are used in many states. Here a statistical relationship between IQ and achievement is considered, allowing for equal probability of identification of an LD across IQ levels, thereby potentially enhancing identification rates. Research in the 1990s, however, failed to demonstrate valid differences on school-related measures between poorly achieving groups of students with an IQ/achievement discrepancy and those with poor school performance and no discrepancy.

Learning Disability Subtypes

There are many different subtypes of learning disabilities. Byron Rourke, writing in 1993, reported three major groupings: (1) reading/spelling, (2) arithmetic, and (3) reading/spelling/arithmetic. Larry Silver, also writing in 1993, suggested a model that includes input disabilities (visual/perceptual, auditory/perceptual, and sensory integrative), integrative disabilities (sequencing, abstraction, and organization), memory disabilities, and output disabilities (language and motor). Reading/spelling disabilities are by far the most prevalent form, with such disabilities estimated to comprise from 5 percent up to 17 percent of the child and adolescent population. Estimates for the occurrence of disorders of written expression range from 2 percent to 8 percent. Although the prevalence of arithmetic LDs ranges from 1 percent to 6 percent, it is not clear whether weak mathematics performance is due to the quality of instruction or an actual LD.

Nonverbal LDs are often overlooked, occur less frequently than reading disorders, and are characterized by problems in arithmetic computation, graphomotor skills, reading comprehension, math reasoning, science, complex concept formation, visual memory, and social-behavioral skills; these are often found in children with white-matter disorders, and are assumed to be more right-hemisphere-based. As of the late 1990s, a classification schema (based on reading disability/dyslexia research) was applied to all achievement domains included in federal and state definitions of LD. Three major types of LDs were identified: specific language impairment, specific reading disability/dyslexia, and specific math disability.

The area of greatest knowledge is reading disorders. These fall into two main groupings: phonological (dysphonetic) and orthographic (dyseidetic). The former is more prevalent and is characterized by deficits in decoding and word analysis, with guesses made based on the initial letter of the word and misspellings being phonetically inaccurate. Shaywitz wrote in 1998 that a deficit in basic phonemic awareness (inability to segment phonemes [the smallest unit of sound] into phonological units) is the underlying cause in virtually all cases of dyslexia. The orthographic reading disability subtype involves an inability to develop a memory for the whole word (gestalt), with visuospatial reversals occurring (e.g., "was" read as "saw") and misspellings being phonetically accurate. There also is a mixed reading disorder, which consists of characteristics found in both types of deficit. The major new finding is that reading disabilities are more strongly associated with auditory rather than visual deficits.

Causes and Diagnosis

With regard to causes, research extends to family, genetic, and neuroanatomic bases, with most work being done in language and reading disabilities. There appears to be heritability in language and reading LDs, with similar LDs being found in 35 percent to 45 percent of first-degree relatives. Also, identical twins are more likely to have similar LDs than fraternal twins. Chromosomes 6 and 15 have been implicated frequently as possible genetic causes of LDs. Neuroimaging techniques, such as functional magnetic resonance imaging, have documented differences among dyslexic and nonreading-disabled individuals. Studies have found that in individuals with dyslexia, certain areas of the brain are different than in individuals without dyslexia. Nonetheless, there are no neuroanatomic or neuroelectric diagnostic tests that identify LDs in the brain. Although LDs are found more frequently in children subject to brain insult (such as premature birth and asphyxia), many children display LDs without any identifiable cause.

Outcomes

Learning disabilities do not disappear; rather, students compensate and learn bypass strategies, allowing for academic progress. The long-term outcome is variable, depending on the type of LD, degree of impairment, intelligence, environment, type of interventions provided, and presence of other disorders. For example, in the case of dyslexia, students often show improvement, but the underlying deficits in phonemic awareness skills prevent the individual from reading in an "automatic," appropriately speeded fashion.

Conclusions

To adequately understand an LD, the following areas must be considered: educational achievement, educational opportunity, cognitive functioning, potential emotional issues, peripheral sensory and neurological function (e.g., vision, hearing), family history, academic history, and age of onset of the LD. More specific tests need to be employed as necessary. Only in this way can a proper diagnosis and effective intervention plan be made.

See also: DEVELOPMENTAL DISABILITIES

Bibliography

American Academy of Child and Adolescent Psychiatry. "Practice Parameters for the Assessment and Treatment of Children and Adolescents with Language and Learning Disorders." Journal of the Academy of Child and Adolescent Psychiatry 37 (1998 supplement):46S-62S.

American Psychiatric Association. The Diagnostic and Statistical Manual of Mental Disorders: DSM-IV. Washington, DC: American Psychiatric Association, 1994.

Aylward, Glen. Practitioner's Guide to Developmental and Psychological Testing. New York: Plenum Medical, 1994.

Kavale, K. A., and S. R. Forness. The Nature of Learning Disabilities: Critical Elements of Diagnosis and Classification. Mahwah, NJ: Erlbaum, 1995.

Mather, Nancy, and William Healy. "Deposing Aptitude-Achievement Discrepancy as the Imperial Criterion for Learning Disabilities." Learning Disabilities 1 (1989):40-48.

Morris, Robin, Karla Stuebing, Jack Fletcher, Sally Shawitz, G. Reid Lyon, Donald Shankweiler, Leonard Katz, David Francis, and Bennett Shaywitz. "Subtypes of Reading Disability Variability around a Phonological Core." Journal of Educational Psychology 90 (1998):347-373.

Padget, S. Y. "Lessons from Research on Dyslexia: Implications for a Classification System for Learning Disabilities." Learning Disability Quarterly 21 (1998):167-178.

Pennington, Bruce. "Genetics of Learning Disabilities." Journal of Child Neurology 10 (1995 supplement):S69-S77.

Rourke, Byron. "Arithmetic Disabilities, Specific and Otherwise." Journal of Learning Disabilities 26 (1993):214-226.

Rourke, Byron. Syndrome of Nonverbal Learning Disabilities. New York: Guilford Press, 1995.

Shaywitz, Sally. "Dyslexia." Scientific American 275 (1996):98-104.

Shaywitz, Sally. "Dyslexia." New England Journal of Medicine 338(1998):307-312.

Silver, Larry. "Introduction and Overview to the Clinical Concepts of Learning Disabilities." Child and Adolescent Psychiatric Clinics of North America 2 (1993):181-192.

Tomblin, J. B., and P. R. Buckwalter. "Studies of the Genetics ofSpecific Language Impairment." In R. Watkins and M. Rice eds., Specific Language Impairments in Children. Baltimore: Paul H. Brookes, 1994.

Glen P. Aylward