Learning Disabilities

Learning disabilities applies to difficulties in reading, mathematics, and written language. Although children with learning disabilities can have difficulty with spoken language and language comprehension, most of the research revolves around the ability to read and understand written information. For further information about oral communication one should look at material in speech and language, which is beyond the scope of this entry.

Learning difficulties can be present in reading (phonics, comprehension), mathematics (calculation, reasoning), language (receptive, expressive), and written expression. Learning disabilities are assumed to be due to central nervous system dys-function (National Joint Committee for Learning Disabilities [NJCLD] 1991) and reflect a discrepancy between ability and achievement.

Diagnosis of Learning Disabilities

The diagnosis of learning disabilities varies depending on where one resides, with different states having different requirements for a learning disability diagnosis. Differences among states vary between psychometric measurement practices, which are called discrepancy models. However, most definitions share the requirement that a significant discrepancy exist between ability and achievement. The Intelligence Quotient (IQ) test becomes an important part of the diagnosis in these definitions. Such a discrepancy model leads to differing numbers of children identified as learning disabled (Sofie and Riccio 2002). Children and adolescents who are in the low average range of intelligence have a more difficult time qualifying for services as they must score very low on an achievement test in order to qualify (Semrud-Clikeman et al. 1992).

Children who have language difficulties frequently score poorly on the verbal portion of the IQ test, thus lowering their scores (Aaron 1997; Morris et al. 1998; Siegel 1992). These children and those from backgrounds other than the middle and upper class may be penalized by standardized tests that are far from culture-free (Greenfield 1997; Siegel 1990; Stanovich 1986). The highest concentration of poor readers has been found in certain ethnic groups and in poor urban neighborhoods (Snow, Burns, and Griffin 1998). Children from impoverished backgrounds or those from a different culture may not have acquired sufficient knowledge in order to answer the IQ test questions correctly. In fact, research has found that many of these children are not classified as learning disabled but rather as slow learners and often not considered bright enough to profit from remediation (Siegel 1990). The current methods of diagnosing children with learning disabilities assume that intelligence is a prerequisite for reading attainment. Research has indicated that IQ scores account for only 25 percent of the variance in reading scores and, as such, is not an important variable in predicting how a child will read (Aaron 1997; Swanson, Hoskyn, and Lee 1999). R. Valencia (1995) found that major achievement tests may underestimate the learning of minority children, particularly those whose primary language is not English. A study found that IQ explained only 6 percent of the variance of a Hispanic child's variance and only 10 percent of an African-American child's grades (Figueroa and Sassenrath, 1989).

Some authors suggest that children reading below grade level should be provided with reading support no matter what ability level they possess. Sally Shaywitz and her colleagues (1992) found that reading disabilities occur along a continuum with no clear difference between children with reading problems and those usually classified as slow learners. Further research has found more similarities than differences between slow learners and those with learning disabilities with few differences present between these two groups on measures of reading, spelling, and phonics knowledge (Siegel 1990). Linda Siegel concluded that the more the task is related to reading the less important intelligence is to reading achievement.

Assessment Issues

Given the above concerns, it is important to provide a comprehensive evaluation of a child with a possible learning disability. Reading is a multidimensional skill involving the ability to read words from sight, sound out words (phonological coding), read fluently and with good speed, and to understand what is read. In any part of this reading process problems can arise and disrupt the reading process. For example, a child who reads haltingly and needs to sound out almost every word will often experience difficulty with comprehension because it takes so long to read a passage and the child is concentrating on the words rather than the information. Evaluation of this child's reading rate and sight-word vocabulary are important aspects. Reading a passage to him/her and checking the comprehension of the passage assists one in understanding whether difficulties in comprehension are due to true comprehension problems or to the difficulty with the reading process. Similarly a child who has difficulty sounding out words may well have an intact sight-word vocabulary. In this case the child will benefit from using this strength with remediation in phonics.

Comorbidity Issues

Learning disabilities often occur in conjunction with other disorders or conditions. Comorbidity refers to multiple disorders within one individual. Learning disabilities occur concurrently with other conditions (for example, sensory impairment or serious emotional disturbance), but is not a result of the comorbid disorder (NJCLD 1991). For example, a child who is hearing-impaired would not qualify for LD services due solely to the hearing impairment.

Attention deficit hyperactivity disorders (ADHD) and learning disabilities are frequently comorbid. However, the inattention and impulsivity characteristic of ADHD make it difficult to determine if academic difficulty is due to the presence of learning disabilities or is a consequence of attention deficits (Semrud-Clikeman et al. 1992). Language disorders, depression, and anxiety are often experienced by those diagnosed with learning disabilities (American Psychiatric Association 1994). Social skills deficits are also frequently found in children diagnosed with learning disability (San Miguel et al. 1996).

Neuropsychology of Learning Disabilities

Learning disabilities is a heterogeneous disorder. The most common type of learning disability is language-based and due to difficulties with the sounding out of words—also called phonological coding deficits (Teeter and Semrud-Clikeman 1997). In this type of learning disability the child has difficulty hearing and/or understanding the differences in the sounds of a word (Mann 1991). For example, the word cat may not be heard as three different sounds—c a t. Reading requires that a child learn the relationship between the written letters and the sound segments—also called sound-symbol learning (Torgesen 1993). This is the most common type of learning disability.

Another type of learning disability involves difficulty with the visual or orthographic features of a word (Stanovich 1992). For example the outward configuration of words such as left and felt are relatively similar—high letter, low letter, two high letters—and may be confused by a child with this type of learning disability. These types of learning disabilities are less common. Visual memory is important in reading and children with this type of learning disability seem to have difficulty recalling what they see (Terepocki, Kruk, and Willows 2002). Children are evaluated in their ability to discriminate phonetically similar words like main from mane and homonyms (e.g., see and sea).

The majority of learning disabilities are reading based and most of the research involves children with reading disabilities (or dyslexia). However, it is important to realize that learning disabilities can also be identified in mathematics and written language. These types of learning problems are not as commonly evaluated or reported as a reading disability. Written language disabilities can have profound effects on a child's ability to generate and organize ideas in written form (Nodine, Barenbaum, and Newcomer 1985). Less is known about written language disabilities than reading disabilities but a study that evaluated children with brain injuries found that these children had intact reading skills but deficits in mathematics and written language, particularly if the damage was in the right hemisphere.

The incidence of math-based learning disabilities suggests that approximately 6 percent of children show a learning disability in this area (Miles and Forcht 1995). Difficulties can be found in mathematics calculations that are often related to difficulties with visual-spatial skills. Children with this type of disability may also show difficulties with social understanding. When mathematics problems and visual-spatial delays occur together, the child may have a nonverbal learning disability. These difficulties involve the child's inability to understand the context of the social situation, to interpret facial and body gestures, and to act accordingly. The relationship between the mathematics difficulties and these social deficits is not fully understood and further research is needed in this area (Semrud-Clikeman and Hynd 1990).

Neuro-Imaging and Learning Disabilities

Differences in brain anatomy have been consistently found in the area where sound-symbol relationships are believed to take place. Neuroimaging has now allowed further evaluation of the brain in living children. Studies found differences in the area of the brain responsible for sound-symbol interpretation (Hynd et al. 1990) as well as in the left hemisphere and frontal areas of the brain believed to be responsible for speaking ( Jernigan et al. 1991; Semrud-Clikeman et al. 1991). Neurons were found to be out of place, additional neurons in places where they should not be were found, and smaller volumes of the planatemporale were found. This area is responsible for auditory processing (Hynd and Semrud-Clikeman 1989). Such regional differences imply a neurodevelopmental process that went awry during gestation rather than brain damage or environmental influences. It is important to note that this asymmetry/symmetry may not be solely responsible for learning disabilities, although it is likely a major contributor to such difficulties (Morgan and Hynd 1998; Steinmetz and Galaburda 1991).

Electrophysiology and Learning Disabilities

Electrophysiological techniques have also been used in the study of learning disabilities to examine the neurobiological mechanisms that underlie these disabilities. The brain has ongoing electrical activity whose waveform can be measured and recorded. Large populations of neurons are measured by electrodes placed on the scalp with changes in the ongoing waveform occurring in response to a cognitive event, such as attention or stimulus discrimination.

Several decades of research have demonstrated different patterns of activation in the brains of children with learning disabilities and those of control groups. Abnormal electrical responses have been found in populations with learning disabilities when they are asked to process phonological information. Studies of components not involving conscious processing have demonstrated that adults and children with reading disabilities process auditory information differently than do normal readers. These components occur later in subjects with learning disabilities, indicating low-level auditory processing deficits. (McAnally and Stein 1996; Baldeweg et al. 1999). This physiological abnormality has also found to be correlated with phonological deficits.

Genetics of Learning Disabilities

The genetics of learning disabilities became of an area of significant interest beginning in the 1990s. Reading disabilities run in families and this familiarity may be due in part to genetic influences and in part to environment. These genetic influences are likely to have a direct impact on the development of the brain or a specific region of the brain that is probably involved in language.

Genetic influences appear to be more prominent in children with phonological coding deficits than in those with visual coding deficits (Pennington 1991). These studies have been generally involved identical and fraternal twins. Deficits in specific processes have been found in phonological coding (the ability to discriminate sounds in words) and phonemic analysis (the ability to sound out words) compared to in visual-spatial deficits (DeFries et al. 1991). The concordance of phonetically based learning problems was 71 percent for identical twins but only 49 percent for fraternal twins. Bruce Pennington and his colleagues (1991) found evidence of a major gene transmission in a large sample of families with reading disabilities linking a small set of genes that indirectly affect reading. Although chromosomes 6 and 15 have been linked to reading problems, it is likely that the difficulty is due to several genes that have not been fully evaluated (Smith, Kimberling, and Pennington 1991). Genetic analysis of children with mathematics or written expression disabilities is another area that requires study.

Environmental influences also impact the brain and culture may change the development of neurons in a specific manner (e.g., reading left to right rather than right to left). Arabic and Hebrew readers have been found to show differences in hemispheric activation on reading tasks—particularly tasks that involve orthographic processing (Eviatar 2000). In addition, preliminary studies have indicated that those readers that read right to left do not show the same right hemispheric preference for the processing of faces and emotion as do those who read left to right (Eviatar 1997; Vaid and Singh 1989). Genetics and neuro-imaging studies may provide more information about these differences.

Familial risk for learning disabilities is clearly significant and substantial in many of the research findings (Gilger, Pennington, and DeFries 1991). Environment may play a role in the development of reading disabilities but no difference has been found between preschool literacy rate in children with reading problems and those without reading problems (Scarborough 1991). What has been found that within the family, the child with a predisposition for a reading problem is less interested in reading and reading-like activities than those without such a predilection (Scarborough, Dobrich, and Hager 1991). Moreover, differences in amount of time being read to, looking at books, and listening to stories were found between siblings with and without later reading difficulties.

Family Aspects of Learning Disabilities

The discussion of the genetics of learning disabilities leads into family aspects as many parents also have a learning disability. It is important to recognize this possibility, particularly when developing interventions and recommendations for these families. It may be unrealistic to ask a parent who also has a learning disability to read to their child, as the action may be fraught with anxiety and difficulty for the parent. It is also important to realize that parents who experienced difficulty in learning themselves may find coming to a school for a parent-teacher conference to be frightening and intimidating (Semrud-Clikeman 1994).

There are few studies in this area but prenatal and postnatal factors have been found to be important in the development of learning problems in the first two years of life (Werner and Smith 1981). Families that were characterized as chaotic or in poverty showed a higher probability of children experiencing learning problems than those without—these variables become more significant as the child becomes older (Teeter and Semrud-Clikeman 1997). Socioeconomic status, home conditions, and educational level of family members appear to act either as complicating factors or as compensatory factors for children with reading problems (Badian 1988; Keogh and Sears 1991).

Robert Jay Green (1992) draws from biological, sociological, and familial sources in evaluating the impact of families on achievement and learning. He suggests that each of these factors interact with one another and either improve learning or impede skill development. These factors work less strongly on biologically based difficulties (e.g., genetically based type of learning disability) than on those environmentally based. However, difficulties in learning and attention are due to the influences of many genes and may well respond to environmental changes that can assist the child in over-coming learning difficulties in an environment that is helpful and exacerbate the difficulties in a less than optimal environment. Green's (1992) model assumes that achievement difficulties can be partially caused or maintained by family factors as well as those present in the school system and social environments. Given these concerns it is important to link school-based interventions with family support.

Interventions

Children with phonological coding deficits appear to respond well to interventions that stress direct training of phonics and place the training within a context (Cunningham 1990). Such a context—metacognitive training—allows the child to learn when to use a particular tactic and how to decide if it is effective (Cunningham 1989). The Reading Recovery Program (Clay 1993) has shown good promise in assisting children with their learning. The program emphasizes understanding the reading process in addition to emphasizing decoding skills. Teaching word families within this context has also been found to be helpful (i.e., an, in, fan, tan, or man).

Early identification of children at risk for learning difficulties is also recommended with specific training in phonemic awareness, rhyming skills, and word families provided in preschool and kindergarten (Felton and Pepper 1995; Wise and Olson 1991). Such early intervention has been found to be most appropriate for children with a family history of learning disabilities (Scarborough 1991). These children demonstrate early on difficulties in language, both in understanding and expressing their thoughts, that later translates into problems in reading readiness (Wise and Olson 1991). Programs, such as FastForword, LindamoodAuditory System, and the Slingerland or Orton-Gillingham method, are helpful to some children with learning disabilities. Websites can be readily found for each of these interventions.

Conclusion

Learning disabilities is a field that is constantly changing. With the advent of techniques that allow scholars to study the brain in action, we may understand not only the normal process of reading but also what happens when the system is not working. The hope is that we will be able to prevent learning disabilities or, at the least, to develop innovative and successful interventions. It is also hoped that we will become more adept at identifying children at earlier ages to prevent some of the emotional and social difficulties that can be associated with a learning disability. Neuroscience is now promising new avenues in our study of learning disabilities as is genetics. Families who have a history of learning disability need further study to provide appropriate support for them as well as to assist with early interventions. Schools are becoming more adept at working with children with differing types of learning disability and it is hoped that our ability to assess minority children appropriately will also improve.

See also:Academic Achievement; Chronic Illness; Development: Cognitive; School

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MARGARET SEMRUD-CLIKEMAN

KELLIE HIGGINS