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Experts believe there are several types of dyslexia that can cause varying degrees of disability in spelling, reading, writing, and even doing mathematics. Auditory dyslexia, also known as dysphonetic dyslexia, typically occurs when the person has problems connecting letters or letter combinations with their appropriate sounds. Visual dyslexia, also sometimes called dyseidetic dyslexia, usually affects the way a person sees written language.
Other types can include semantic dyslexia, which is normally defined as an impairment in the ability to understand word definitions, and neglect dyslexia, which can cause sufferers to inadvertently drop letters from the ends or beginnings of words when reading. While a person suffering from mild dyslexia may have only one of the disabilities associated with the condition, more severe kinds of dyslexia could leave a person facing more than one of these disabilities at once.
Most people with dyslexia suffer from a decreased ability to read, write, and spell. Not all types of dyslexia manifest in difficulty with language, however. Dyscalculia, a condition believed to be a kind of dyslexia, generally impairs a person's ability to comprehend numerical symbols and perform basic mathematics, even if that person's ability to comprehend more advanced mathematical ideas remains unaffected. Some people with dyslexia may also suffer from dysgraphia, which generally impairs the person's ability to write letters correctly and spell words. It is considered very possible, however, for a person to suffer from a dyslexia-related reading disability without experiencing any writing, speech, or spelling impairments.
Primary dyslexia, secondary dyslexia, and trauma dyslexia are believed to be the three main varieties of dyslexia that can cause these impairments. Primary dyslexia is generally considered hereditary and probably afflicts more men than women. Experts think this type of dyslexia happens because of a left-brain dysfunction. Many people with this kind of dyslexia will be able to learn to read, spell, write, and perform basic mathematics problems, but will generally never be able to progress beyond the level of a normal nine or ten-year-old child.
Secondary dyslexia is a type of dyslexia that is believed to occur due to problems in early childhood or even fetal development. It is also believed to affect more men than women. With specialized education techniques and training, many people with secondary dyslexia find their impairments greatly diminished by the time they reach adulthood.
Trauma dyslexia is a type of dyslexia that can affect those who suffer trauma to the reading and writing centers of the brain. It usually only occurs after an injury to the head, and is therefore usually more common in adults than in young children.