Dyslexia
Dyslexia is a specific learning disability that is neurobiological in origin. The condition is best explained as a language-based disorder that interferes with the learning and processing of language. Varying in degrees of severity, an individual with dyslexia will often have difficulties in processing and comprehending spoken language, expressing themselves, phonological processing, reading, writing, spelling, handwriting, and/or sometimes in arithmetic. Individuals with dyslexia will also often have poor working memory.
Dyslexia is not the result of lack of motivation, sensory impairment, inadequate instructional or environmental opportunities, but may occur together with these conditions. Individuals with dyslexia often have average or above IQ.
Causes of dyslexia
With a strong genetic basis, most cases of dyslexia are hereditary (although the gene is not always inherited directly from the parent – sometimes the parent will have a sibling or immediate relative with the disorder). Researchers have determined that a dominant gene on part of chromosome #6 is responsible for causing neurological differences in individuals with dyslexia.
It is also possible for dyslexia to occur after birth, particularly in young children whose auditory processing development has been disrupted (i.e. through ear infections). Sound reception and phonological awareness may be compromised, which can lead to acquired dyslexia.
The neuroscience of dyslexia
Brain imaging techniques show that individuals with dyslexia have a larger right-hemisphere than those of non dyslexic individuals. This may be one reason why people with dyslexia often have significant strengths in areas controlled by the right-side of the brain such as:
- artistic ability
- athletic ability
- amusical bility
- mechanical ability
- 3-D visuo-spatial skills
- vivid imagination
- intuition
- good people skills
- creative problem solving skills
In addition to this unique brain architecture and unusual wiring, functional magnetic resonance imaging (fMRI) - a type of specialized MRI scan - studies have also shown that non dyslexic readers consistently use the same part of their brain when they read. Individuals with dyslexia however do not use that part of their brain when reading; in fact there appears to be no consistent part used among dyslexic readers. It is therefore assumed that people with dyslexia are not using the most efficient part of their brain when they read.
Different types of dyslexia
No two people will present with identical symptoms of dyslexia. In addition to varying degrees of severity and scope of symptoms, we can also to differentiate between two broad categories (subtypes) of the problem:
▪ Phonological Dyslexia (also known as Dysphonetic Dyslexia) – problems with letter–sound integration (auditory-linguistic).
▪ Visual Dyslexia (also known as Dyseidetic Dyslexia) – problems with perceiving words as a whole (visual-spatial).
The majority of people with dyslexia fall into the first category only (over 60%), with the next highest percentage of sufferers possessing both subtypes of problems (over 20%). It is rare that dyseidetic dyslexia exists on its own (less than 10%), leaving a few cases that remain unclassified.
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