Contrary to some beliefs, it is not caused by eye or vision problems. Dyslexia is a specific information processing problem. It doesn't interfere with how a person thinks or understand complex ideas. Most dyslexic people have normal intelligence, and many have above-average intelligence.
Developmental Reading Disorder (DRD) may appear in combination with developmental writing disorder and developmental arithmetic disorder. All of these involve using symbols to convey information. These conditions may appear alone or in any combination. DRD often runs in families.
In the December 22 issue of Neuron (a journal published by Cell Press), they note that although disrupted processing of speech sounds has been implicated in the underlying pathology of dyslexia, the basis of this disruption and how it interferes with reading comprehension has not been fully explained. The published research finds that a specific abnormality in the processing of auditory signals accounts for the main symptoms of dyslexia.
There are four types of dyslexia (see video):
- Phonological Dyslexia - Difficulty separating component parts of a sentence (syllables, sounds, etc).
- Orthographic Dyslexia - Problem with writing such as spelling patterns
- Dyscalculia - Problem with basic sense of number and quantity and difficult retrieving rote math facts.
- Dysgraphia - Disorder which expresses itself primarily through writing or typing.
Video: What is it like to have Dyslexia
"It is widely agreed that for a majority of dyslexic children, the main cause is related to a deficit in the processing of speech sounds," explains senior study author, Dr. Anne-Lise Giraud and Franck Ramus from the Ecole Normale Supérieure in Paris, France. "It is also well established that there are three main symptoms of this deficit: difficulty paying attention to individual speech sounds, a limited ability to repeat a list of pseudowords or numbers, and a slow performance when asked to name a series of pictures, colors, or numbers as quickly as possible. However, the underlying basis of these symptoms has not been elucidated."
The team looked into whether an abnormality in the early steps of processing of auditory signals in the brain, called "sampling" is linked with dyslexia. They focused on the idea that an anomaly in the initial processing of phonemes, the smallest units of sound that can be used to make a word, might have a direct impact on the processing of speech.
Video: Types of Dyslexia
The researchers found that typical brain processing of auditory rhythms associated with phonemes was disrupted in the left auditory cortex of dyslexics and that this deficit correlated with measures of speech sound processing. Further, dyslexics exhibited an enhanced response to high-frequency rhythms that indirectly interfered with verbal memory. It is possible that this "oversampling" might result in a distortion of the representation of speech sounds.
"Our results suggest that the left auditory cortex of dyslexic people may be less responsive to modulations at very specific frequencies that are optimal for analysis of speech sounds and overly responsive to higher frequencies, which is potentially detrimental to their verbal short-term memory abilities," concludes Dr. Giraud. "Taken together, our data suggest that the auditory cortex of dyslexic individuals is less fine-tuned to the specific needs of speech processing."
Video: Dyslexia Awareness
Dyslexia is a difficult disorder to have as a child. People tend to misunderstand it and incorrectly label the child as a slow learner. These children may grow up with poor self esteem, shy, and aloof. Learning disorders, such as DRD, tend to run in families. Affected families should make every effort to recognize existing problems early. There are a lot of programs for those affected with DRD and early intervention will provide the best possible outcome.
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