CEREBRAL DOMINANCE THEORY by JORDI MAS
One of the earliest and best know of the neurological theories
concerns cerebral dominance: the ability of one portion of the brain to
predominate in controlling certain behaviors.
The human brain is divided into left and right hemispheres,
each having primary duties, In most people the right hemisphere is mainly
responsible for nonverbal, perceptual abilities. Damage to the right brain
can cause impaired judgment of tonal patterns and special directions, and
poor recognition of geometric designs. The left hemisphere regulates verbal
functions, including speech, comprehension, or writing and reading abilities.
An interesting relationship exist between the hemispheres
regulating language function and hand preference. The vast majority of
people (about 93%) are right-handed, nearly all having language controlled
by the left side of the brain. But only about 70% of left-handed people
have language controlled by the left hemisphere; the others have language
function in the right brain or divided among the two hemispheres.
The cerebral dominance theory maintains that the failure
of a single hemisphere to dominate verbal functions the perception of graphic
symbols and the language functions associated with reading- results in
dyslexia. Proponents of the theory believe that in the normal brain visual
imprints made on the verbal dominant hemisphere are used to build associations
between letters and spoken words. If for some reason the verbal controlling
hemisphere fails to dominate verbal functions, the person also perceives
the visual imprints simultaneously made upon the nonverbal hemisphere.
These imprints, however, appear backward, as if viewed through a mirror.
A child with poorly established cerebral dominance, so the theory goes,
is unable to interdirection in wich they are perceived (d for b, saw for
was).
Since about 30% of left-handed persons have language located
in the right or inboth hemispheres, cerebral dominance research has sometimes
identified these individuals as prime candidates for dyslexia. Tests for
hemispheric dominance have been conducted by noting preferences in listening,
clapping, jumping, sighting with one eye, and balancing on one foot. Failure
to demonstrate a decided preference for one side or the other, the theory
maintains, indicates a defect in brain development wich is fully or partially
responsible for dyslexia.
Solid evidence to support the cerebral dominance theory has
been lacking. Most recent studies have not supported the concept that dyslexia
children differ greatly from normal readers in right-hand or left-hand
preferences.
Comentarios a Jordi Màs en jorgemas@intercom.es
Atrás