What is Dyslexia?

Dyslexia is a neurobiological condition that causes difficulties in quite specific areas of learning. It usually affects reading, writing, and spelling, but can also have a negative impact on math skills. The condition is sometimes hard to define because dyslexia can overlap with other learning difficulties that affect spoken language and motor skills.

However, there are typical symptoms that should alert parents, teachers, and others to the possibility that a child, or an adult, has dyslexia.

Until recently, the causes of dyslexia were not well understood. However, it is now known that people coping with dyslexia process information in ways that differ from the rest of the population.

Here is the definition of dyslexia used by the National Institutes of Health and the International Dyslexia Association:

Dyslexia is a specific learning disability that is neurological in origin. It is characterized by difficulties with accurate and/or fluent word recognition, and by poor spelling and decoding abilities.

These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.


There are three main types of dyslexia, each with its own symptoms and causes.

  • Dyseidetic Dyslexia

    A type of dyslexia associated with brain functions located in the angular gyrus of the left parietal lobe of the brain. A person suffering from this type of dyslexia will have poor sight-word recognition, contributing to a slow, laborious reading experience. Irregular words are both sounded out phonetically (laugh = log) and spelled phonetically (ready = rede). As a result of their condition, dyseidetic dyslexics often are more advanced in reading than in spelling.

  • Dysphonetic Dyslexia

    A type of dyslexia associated with functions located in Wernicke's Area of the left temporal lobe. A person suffering from this type of dyslexia relies on sight recognition to read, being unable to sound out unknown words. During reading, words are either known or not known, and are often substituted or skipped when trouble arises. Words are learned by rote memorization, and cannot be spelled by their sound. Ear infections can cause some problems.


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