Different Types of Dyslexia

The Dyslexia types -- Putting Names on the Heads of the Many-headed Beast!

The term 'dyslexia', from 'dys', meaning wrong or problematic and 'lexia' pertaining to words and letters, literally refers to any type of problem in reading. But in medical definitions and common usage the term dyslexia is used to refer to any of several different classes of problems in processing images and sounds.

For clarity of diagnosis and reference these classes of problems are sorted and grouped into various "dyslexia types".

Specifically, dyslexia refers to systematic neurological difficulties in processing images and sounds into useful understood data. The eyes may see fine, but the brain cannot easily decipher the signals it receives from the eyes regarding written words and translate that into the corresponding sounds of spoken words.

There are several different dyslexia types, different classifications of the nature of these translation and interpretation problems.

The most prominent and best known dyslexia types are:

Surface dyslexia. The symptoms of this form manifest themselves as systematic mistakes in going from the written word to the pronounced word. This is particularly apparent in various area where the English language has rules of pronunciation that are inconsistent.

For example, "jowl" might be read as though it rhymed with "bowl", "furlough" might be read as though it rhymed with "tough" or "petty" could be read as though it rhymed with "pretty".

Phonological dyslexia. Symptoms are an inability and failure to grasp and master the phonic nature of the English language. Individuals with this form have severe problems reading new or nonsensical words. This is because they cannot grasp the linkage between the individual sounds or phonemes of the spoken word and the individual or grouped letters on the printed page.

Double-Deficit Dyslexia is the name given to the condition of those individuals who have both Surface Dyslexia and Phonological Dyslexia.

Auditory Dyslexia and Visual Dyslexia both originate from the magnocellular theory of dyslexia. This theory is based on the belief that dyslexics have neurological weaknesses in the magnocellular cells of the area of the brain known as the thalamus. This specific area is where rapid processing of visual and auditory information takes place.

Studies have shown that dyslexics apparently do have weaknesses in their visual and auditory processing. But while these weaknesses may stem from the same area of the brain, they are not uniform or balanced; they are not present to the same degree.

As a result, these two dyslexia types are closely related. For example, a child with poor hearing skills but with average visual skills may be diagnosed as having Auditory Dyslexia, whereas one with poor visual skills but average hearing may be diagnosed as having Visual Dyslexia.

Then finally, there is Orthographic Dyslexia. Orthography is term applied to the set of symbols or letters that make up a language. In English and other European Languages this is the 26-30 or so letters of the alphabets of the specific languages. In Japanese, Chinese or other oriental languages it covers thousands of different characters and symbols.

And so Orthographic Dyslexia relates to problems in identifying and manipulating letters and/or symbols in reading, writing and spelling.

Jorge Chavez