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 example, 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 dysphoneidetic but not dyseidetic dyslexics exhibit a magnocellular pathway defect.


OBJECTIVE
The purpose of this study was to expand our previous work 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 functions were determined with a flickering stimulus (5, 10, 15, 20, and 25 Hz) by using a temporal, two-alternative, forced-choice technique.


RESULTS
The results indicate that the dyseidetic dyslexics do not have a magnocellular pathway defect, whereas the dysphoneidetics do. Furthermore, examination of the individual dysphonetics indicated that the more severely affected subjects also exhibited a magnocellular pathway defect.


CONCLUSIONS
These results suggest that treatment strategies for dyslexics may need to be modified to take into account their specific subtype.
Ridder
W H
WH
Southern California College of Optometry, Fullerton, USA.
Borsting
E
E
Cooper
M
M
McNeel
B
B
Huang
E
E
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D002648:Child; D015350:Contrast Sensitivity / Q000502:physiology*; D004410:Dyslexia / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation; D012684:Sensory Thresholds; D014795:Visual Pathways / Q000503:physiopathology*; D014832:Voice Disorders / Q000503:physiopathology