The term dyslexia is used a lot these days. You hear that a friend's child has dyslexia, or you see a person who is dyslexic on television, or you read that Albert Einstein and Thomas Edison had dyslexia. The word dyslexia, which means "developmental word blindness," has a medical sound to it, but until recently there was little convincing evidence to show that it was medically based. Thanks to the development of computerized imaging techniques, such as functional magnetic resonance imaging (fMRI) and positron-emission tomography (PET scan], as well as recent studies of twins (Olson, 2006), evidence of an organic, genetic basis for dyslexia is beginning to accumulate.
Recent studies using computerized imaging show that the brain activity of students with dyslexia differs from that of students who are good readers (Shaywitz, 2003; Shaywitz & Shaywitz, 2007; Simos et al., 2007). For example, from an early age and often into adulthood, dyslexics show a pattern of underactivation in a region in the back of the brain that enables first accurate and then automatic reading. This pattern of underactivity appears to be present in dyslexics regardless of their age, sex, or culture (Shaywitz, 2003). That is why dyslexics have problems initially "cracking the code" and then problems later on developing reading fluency.
Studies of twins, sibling analysis, and family pedigree analysis have confirmed a genetic basis for learning disabilities (Fiedorowicz, 2005; Olson, 2006). Twin studies have shown that if one twin has a reading disability, the probability of the other twin having a reading disability is 68 percent for identical twins and 40 percent for fraternal twins. Studies also have shown that if there is a family history of dyslexia, the probability of an offspring having a reading disability is significantly increased (Fiedorowicz, 2005). While specific chromosomal links have been hypothesized, no definite conclusions about the genetic transmission of reading disabilities have been reached.
Knowing the cause of severe reading problems is one thing; knowing what to do to help students who have these problems is another altogether. Put very simply, students with dyslexia have serious problems learning to read despite normal intelligence, normal opportunities to learn to read, and an adequate home environment. Although the precise organic cause of dyslexia continues to be researched, considerable evidence suggests that reading problems associated with dyslexia are phonologically based (Blachman, 1997; Foorman, 2003; Stanovich & Siegel, 1994). Students with dyslexia have difficulty developing phonemic awareness, the understanding that spoken words are made up of sounds. Phonemic awareness problems make it hard for these students to link speech sounds to letters, ultimately leading to slow, labored reading characterized by frequent starts and stops and multiple mispronunciations. Students with dyslexia also have comprehension problems largely because their struggle to identify words leaves little energy for understanding what they read.
Students with dyslexia also have trouble with the basic elements of written language, such as spelling and sentence and paragraph construction. Finally, students with dyslexia may have difficulty understanding representational systems, such as telling time, directions, and seasons (Bryan & Bryan, 1986). Dyslexia commonly is considered a type of learning disability, and students with dyslexia are served under the learning disability classification of IDEA.
It is important to identify students with dyslexia and other severe reading disabilities early, before they fall far behind their peers in word-recognition reading skills. Early identification is particularly urgent given recent studies showing that effective language instruction appears to generate repair in underactivated sections of the brain (Shaywitz, 2003; Simos et al., 2007). The recent movement toward identifying reading disabilities based on children's response to intervention (RtI) will likely help schools to identify children earlier than the traditional approach of establishing a discrepancy between children's ability and reading achievement. This is because schools using a discrepancy model often have to wait for children to get older to have a large enough discrepancy between achievement and ability to be eligible for special education services. In this way, students who appear to be learning letter names, sounds, and sight words at a significantly slower rate than their classmates can receive intensive support as early as kindergarten.
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