Abstract
M.A. (Psychology)
The goal of the present study was to determine whether there exist any
differences in cognitive skills between left-handed dyslexic boys and righthanded
dyslexic boys with left hemisphere speech representation. The
comparison was made in terms of their verbal and visuo-spatial skills.
The motivation for this study resulted from a hypothesis that was formulated by
Geschwind and Behan (1982). The hypothesis states that there exists a
difference in functional hemispheric asymmetry between left-handed and righthanded
dyslexic boys with left hemispheric language representation. By virtue of
their explanation of dyslexia in terms of a prenatal hyper secretion of the
hormone called testosterone, Geschwind and Behan state that left-handed
dyslexic boys will perform better than right-handed dyslexic boys on visuospatial
tasks.
An empirical study was performed in order to compare the verbal and visuospatial
skills of left-handed and right-handed dyslexic boys. Twenty-six lefthanded
and 26 right-handed dyslexic boys served as the experimental subjects.
All the subjects had left hemispheric language representation. The selection of
the experimental subjects was done by means of the dichotic listening technique
as well as with the Harris test of lateral dominance.
The nine subtests of the Senior South African Individual Scale-Revised served
as measuring-instrument. The first five subscales represented the verbal
cognitive skills. The visuo-spatial skills were measured with subtests six to nine.
The data were statistically analysed by means of Hotelling's T2-test and
Student's t-tests.
The results indicated that there were no statistically significant differences
between left-handed and right-handed dyslexic boys with left hemispheric
language representation in terms of any of the verbal and visuo-spatial
subtests.
The relationship between hand preference, functional hemispheric asymmetry
and dyslexia is elucidated by the present study which rejects the GeschwindBehan
hypothesis that there exists a difference in functional hemispheric asymmetry between left-handed and right-handed dyslexic boys. A previous
study (Hugdahl et aI., 1989) accepted this hypothesis. Further research is thus
necessary in order to determine the validity of the Geschwind-Behan
hypothesis.