WAYS OF LOOKING AT DYSLEXIA

There are many definitions of the disorder called dyslexia but no consensus. The World Federation of Neurology defined dyslexia as follows:

Specific developmental dyslexia is a disorder manifested by difficulty learning to read despite conventional instruction, adequate intelligence, and adequate sociocultural opportunity. It is dependent upon fundamental cognitive disabilities that are frequently of constitutional origin.

Some of the other published definitions are purely descriptive, while still others embody causal theories. From the varying definitions used by dyslexia researchers and organizations around the world, it appears that dyslexia is not one thing but many, insofar as it serves as a conceptual clearing-house for a number of reading skills deficits and difficulties, with a number of causes.

Castles and Coltheart, 1993, described phonological and surface types of developmental dyslexia by analogy to classical subtypes of acquired dyslexia (alexia) which are classified according to the rate of errors in reading non-words.

However the distinction between surface and phonological dyslexia has not replaced the old empirical terminology of dysphonetic versus dyseidetic types of dyslexia.

The surface/phonological distinction is only descriptive, and devoid of any aetiological assumption as to the underlying brain mechanisms, in contrast the dysphonetic/dyseidetic distinction refers to two different mechanisms:— one relates to a speech discrimination deficit, and the other to a visual perception impairment.

Most people with dyslexia who have Boder's Dysiedetic type, have attentional and spatial difficulties which interfere with the reading acquisition process.