Subtypes of dyslexia: investigation of Boder's system using quantitative neurophysiology.

Two studies investigated the construct validity of Boder's classification of dyslexic children, using spectral analysis of electroencephalograms recorded during cognitive tasks. Children were classified as being dysphonetic (auditory-phonetic disabilities), dyseidetic (visual spatial disabilities) or mixed (deficient in both processes). The first study examined 21 dyslexic children between seven and 10 years of age and six control children. On three of six cognitive tasks there were significant differences between the dyslexic subgroups, and between the dyslexic and control children. The second study involved 33 eight- and nine-year-old dyslexic children and 31 controls. The results of two of seven cognitive tasks confirmed subtype differences. Significant differences in left temporal-parietal theta activity in the electroencephalograms of the dyseidetic children suggest that their reading disabilities may be the result of over-use of linguistic abilities rather than deficient visual-spatial skills.