Types Of Dyslexia

Traditionally referred to as “slow learning disorders”, many disabilities relating to language processing are now called as Dyslexia. They form a complex group of disorders, the sufferers of which face difficulties in decoding spoken and written words.

In the strictest etymological terms, dyslexia means having problems with reading written text. However, this does not embrace the problem in its entirety which actually includes difficulties in reading, writing, spelling and coordinating among all three. It is believed that almost 5 –10% of the population suffers from some form of dyslexia but exact figures need more documentary evidence.

In addition to difficulty in language processing, dyslexics may have associated hearing deficits, poor short term memory, lack of physical co-ordination, lack of sense of direction and a lack of time sense. Co-existing conditions include dysgraphia, dyscalculia, attention deficit disorders(ADD) and cluttering speech.

In keeping with the basic disorder, Dyslexia can be defined as “A learning disability that is at its core neurological in origin and is symptomatic with difficulties in recognizing letters and words along with poor reading, decoding and spelling abilities.

Dyslexia Types

Classification helps a better understanding of this complex disorder. Classification in turn maybe based on the following

• Aetiology(causes)
• The Pathology or
• The Symptoms.

Aetiological Classification

• Developmental – Developmental Dyslexia is caused by biological anomalies during the prenatal period or in early childhood.
• Acquired – Acquired Dyslexia is caused mainly by cranial trauma in later life and a prime example of adult dyslexia.

Pathological Classification

Stems from the magnocellular theory of dyslexia which postulates that a neurological weakness in the magnocellular area of the thalamus of the brain where rapid processing of visual and auditory cues takes place leads to the manifestations. Accordingly, Dyslexia can be classified into

• Auditory Dyslexia – These individuals have poor hearing or disability in processing auditory cues but will have normal visual processing.
• Visual Dyslexia – Poor visual cue processing but normal hearing.

Symptomatic Classification

• Surface – In this type of disorder, frequent mistakes are seen with inconsistent pronunciations of words that have similar spelling. Eg: Bowl maybe pronounced to rhyme with howl. Even though there maybe recognition of the spelling, there are problems with whole word recognition.

• Phonological – This indicates an inability to grasp the phonic nature of language.There is a pronounced difficulty in reading new words because of an inability to grasp links between individual sounds or phonemes.

• Double Deficit Dyslexia  – Double deficit dyslexia combines the manifestations of both the above types.

Another symptomatic classification based on Border`s Reading-Spelling Pattern is as follows

• Dysphonetic Dyslexia – This maybe regarded as the symptomatic form of auditory dyslexia.Typical sufferers face difficulty in connecting sounds to symbols and also find it difficult to sound out words.Spelling mistakes reveal poor phonetic grasp of the language.There is a problem in mentally processing language.Any disruption in the pathway of hearing can also lead to this type.

• Dysedetic Dyslexia  – This is visual dyslexia in a symptomatic guise.It refers to how a person sees and mentally processes the symbols,letters and word concepts of language into correct written formats.Even with a good grasp of phonetic concepts,sufferers have difficulty with whole word recognition and spelling.Similarity between the intended word and the actual word written will allow the reader to guess at what the word was, but the spelling is still far from correct. Eg: Telephone maybe spelt as telafone.There may also be a transposition or reversal of the letters in a word. Eg: Need maybe written as deen.

• Mixed Dyslexia – Mixed Dyslexia is a combination of the above two with difficulty in processing language audio-visually.This form is not very amenable to correction.

The description of the types of dyslexia would be incomplete without describing “Orthographic Dyslexia”. Orthography relates to the symbols used in the written form of a language. In English, this denotes the 26 letters of the alphabet. In pictographic languages like Chinese and Japanese, it includes thousands of symbols for different words. Orthographic dyslexics have difficulty in identifying and manipulating letters in reading, writing and spelling. Although, they have good phonetic grasp, they are unable to manipulate the letters and respond better to verbal cues.

In conclusion, it would be safe to say that dyslexia is a very general term encompassing a vast spectrum of disorders relating to language and an individualistic approach to each case will be advantageous in understanding and managing each particular patient.