Evidence for deficit in interhemispheric transfer of information in dyslexic boys

Visual thresholds for identification of briefly flashed, lateralized letters were obtained for dyslexics and normal readers, age 11-15 years. Subjects were also tested for ability to localize tactile stimuli on the fingers and transfer information intermanually, a task failed by callosal agenesis patients (Dennis, 1976). Dyslexics differed significantly from normals on both tasks. Half the dyslexics demonstrated high threshold asymmetry across hemifields and many tactile localization errors, a pattern suggesting an "interhemispheric transfer deficit" as a cause of reading failure. Despite equally severe initial handicaps, dyslexics showing low, symmetric thresholds and few tactile errors, showed more reading improvement than did the others.