NOT ALL DYSLEXICS ARE CREATED EQUAL

Background. Dyslexia is a common disorder that has traditionally been treated as a homogeneous condition. However, recent evidence indicates that it is a heterogenous condition with several subtypes. For exampl e, studies of the visual system indicate that not all dyslexics have a normal visual pathway. Approximately 75% have a processing deficit in the magnocellular pathway, Our previous study indicated that dysphone idetic but not dyseidetic dyslexics exhibit a magnocellular pathway de fect, Purpose, The purpose of this study was to expand our previous wo rk by also examining dysphonetic dyslexics, Additionally, the stimulus was altered to enhance detection of a magnocellular pathway defect in any dyslexic subtype, Methods, Temporal contrast sensitivity function s were determined with a flickering stimulus (5, 10, 15, 20, and 25 Hz ) by using a temporal, two-alternative, forced-choice technique, Resul ts, The results indicate that the dyseidetic dyslexics do not have a m agnocellular pathway defect, whereas the dysphoneidetics do, Furthermo re, examination of the individual dysphonetics indicated that the more severely affected subjects also exhibited a magnocellular pathway def ect, Conclusion, These results suggest that treatment strategies for d yslexics may need to be modified to take into account their specific s ubtype.