What Is Dyslexia?
Dyslexia is a neurobiological and genetic condition that causes difficulties in specific areas of learning. Dyslexia affects reading, writing, and spelling. It 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 (movement) skills.
However, there are typical symptoms that should alert parents, teachers, and others to the possibility that a child, or an adult, is dyslexic.
Until recently, the causes of dyslexia were not well understood. However, it is now known that individuals 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. – National Institutes of Health
Dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that involve accuracy, speed, or both… These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual’s peers. The causes of dyslexia are complex and involve combinations of genetic, neurobiological, and environmental influences that interact throughout development. Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges. Secondary consequences include reading comprehension problems and reduced reading and writing experience that can impede growth in language, knowledge, written expression, and overall academic achievement. – The International Dyslexia Association
There are two main types of dyslexia–Dyseidetic Dyslexia and Dysphonetic Dyslexia–each with its own symptoms and causes.
Dyseidetic Dyslexia
A person experiencing this type of dyslexia will have poor sight-word recognition, contributing to slow, laborious reading. Irregular words are usually sounded out phonetically (laugh = log) and spelled phonetically (ready = redee). As a result, individuals with Dyseidetic Dyslexia can be more advanced in reading than in spelling. This type of dyslexia is associated with brain functions located in the angular gyrus of the left parietal lobe of the brain.
Dysphonetic Dyslexia
A person experiencing 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. This type of dyslexia is associated with functions located in Wernicke's Area of the left temporal lobe.