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By: Jabez LeBret
Source: Forbes
Critics:
Dyslexia, previously known as word blindness, is a learning disability (‘learning difficulty’ in the UK that affects either reading or writing. Different people are affected to different degrees.Problems may include difficulties in spelling words, reading quickly, writing words, “sounding out” words in the head, pronouncing words when reading aloud and understanding what one reads.Often these difficulties are first noticed at school.
The difficulties are involuntary, and people with this disorder have a normal desire to learn.People with dyslexia have higher rates of attention deficit hyperactivity disorder (ADHD), developmental language disorders, and difficulties with numbers. Dyslexia is believed to be caused by the interaction of genetic and environmental factors.
Some cases run in families.Dyslexia that develops due to a traumatic brain injury, stroke, or dementia is sometimes called “acquired dyslexia” or alexia.The underlying mechanisms of dyslexia result from differences within the brain’s language processing.
Dyslexia is diagnosed through a series of tests of memory, vision, spelling, and reading skills. Dyslexia is separate from reading difficulties caused by hearing or vision problems or by insufficient teaching or opportunity to learn. Treatment involves adjusting teaching methods to meet the person’s needs. While not curing the underlying problem, it may decrease the degree or impact of symptoms.
Treatments targeting vision are not effective. Dyslexia is the most common learning disability and occurs in all areas of the world. It affects 3–7% of the population; however, up to 20% of the general population may have some degree of symptoms. While dyslexia is more often diagnosed in boys, this is partly explained by a self-fulfilling referral bias among teachers and professionals.
It has even been suggested that the condition affects men and women equally. Some believe that dyslexia is best considered as a different way of learning, with both benefits and downsides. Dyslexia is divided into developmental and acquired forms. Acquired dyslexia occurs subsequent to neurological insult, such as traumatic brain injury or stroke.
People with acquired dyslexia exhibit some of the signs or symptoms of the developmental disorder, but require different assessment strategies and treatment approaches. Pure alexia, also known as agnosic alexia or pure word blindness, is one form of alexia which makes up “the peripheral dyslexia” group. In early childhood, symptoms that correlate with a later diagnosis of dyslexia include delayed onset of speech and a lack of phonological awareness.
A common myth closely associates dyslexia with mirror writing and reading letters or words backwards.These behaviors are seen in many children as they learn to read and write, and are not considered to be defining characteristics of dyslexia.
School-age children with dyslexia may exhibit signs of difficulty in identifying or generating rhyming words, or counting the number of syllables in words—both of which depend on phonological awareness. They may also show difficulty in segmenting words into individual sounds (such as sounding out the three sounds of k, a, and t in cat) or may struggle to blend sounds, indicating reduced phonemic awareness.
Difficulties with word retrieval or naming things is also associated with dyslexia. People with dyslexia are commonly poor spellers, a feature sometimes called dysorthographia or dysgraphia, which depends on the skill of orthographic coding. Problems persist into adolescence and adulthood and may include difficulties with summarizing stories, memorization, reading aloud, or learning foreign languages.
Adults with dyslexia can often read with good comprehension, though they tend to read more slowly than others without a learning difficulty and perform worse in spelling tests or when reading nonsense words—a measure of phonological awareness.
Research into potential genetic causes of dyslexia has its roots in post-autopsy examination of the brains of people with dyslexia. Observed anatomical differences in the language centers of such brains include microscopic cortical malformations known as ectopias, and more rarely, vascular micro-malformations, and microgyrus—a smaller than usual size for the gyrus.
The previously cited studies and others suggest that abnormal cortical development, presumed to occur before or during the sixth month of fetal brain development, may have caused the abnormalities. Abnormal cell formations in people with dyslexia have also been reported in non-language cerebral and subcortical brain structures.
Several genes have been associated with dyslexia, including DCDC2 and KIAA0319 on chromosome 6, and DYX1C1 on chromosome 15. The contribution of gene–environment interaction to reading disability has been intensely studied using twin studies, which estimate the proportion of variance associated with a person’s environment and the proportion associated with their genes.
Both environmental and genetic factors appear to contribute to reading development. Studies examining the influence of environmental factors such as parental education and teaching quality have determined that genetics have greater influence in supportive, rather than less optimal, environments.
However, more optimal conditions may just allow those genetic risk factors to account for more of the variance in outcome because the environmental risk factors have been minimized. As environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability.
Measures of gene expression, histone modifications, and methylation in the human periphery are used to study epigenetic processes; however, all of these have limitations in the extrapolation of results for application to the human brain. The orthographic complexity of a language directly affects how difficult it is to learn to read it. English and French have comparatively “deep” phonemic orthographies within the Latin alphabet writing system, with complex structures employing spelling patterns on several levels:
Letter-sound correspondence, syllables, and morphemes. Languages such as Spanish, Italian and Finnish primarily employ letter-sound correspondence—so-called “shallow” orthographies—which makes them easier to learn for people with dyslexia. Logographic writing systems, such as Chinese characters, have extensive symbol use; and these also pose problems for dyslexic learners.
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