Modification of a dichotomous tactile stimulation technique for left and right hemispheric specialization in normal and dyslexic readers
The present study was designed to investigate the relationship of inferred hemisphericity for spatial and verbal processing in normal and dyslexic male readers using a dichotomous tactile stimulation technique. The study was a modification of Witelson's (1974; 1976) studies using non-verbal (shapes) and verbal (letters) stimuli. An additional verbal (objects) task, in which subjects recognized and verbally reported the object's use, was devised specifically for the study.One purpose of the study was to determine whether older normal readers would differ from dyslexics of the same age and younger normal readers on their accuracy of recognition of stimuli. Another purpose was to examine the differences between left and right hand responses to the verbal tasks (letters and objects) to determine if the objects task was a better measure of verbal or left hemispheric functioning than the letters task.Subjects were right-handed males who demonstrated average or above average intelligence and manifested no sensory impairment or primary emotional disturbance. Older normal readers and dyslexics were 9 to 13 years while younger normal readers were 5 to 7 years old. A total of 66 subjects qualified for and completed the study.Analysis of variance was employed to test the main hypothesis using a three-factor design with repeated measures on the same subjects (Winer, 1971). No differences were found in the accuracy of response among groups suggesting greater within than between group variance. A significant Task x Hand interaction (P/-.05) was explained by greater inferred right hemisphere involvement in the processing of the shapes and letters tasks while greater inferred left hemisphere involvement in the processing of the objects task was confirmed for the normal groups. Dyslexics, however; demonstrated more inferred right hemisphere involvement for all the tasks (shapes, letters and objects) suggesting the use of a spatial-holistic cognitive strategy for stimuli whether non-verbal or verbal.