Developmental Dyslexia and Related Reading Disorders
By Jordi Màs Manjon
Defining Dyslexia
One of the basic problems associated with dyslexia is use
of the term. Early researchers investigating the disorder began to use
"dyslexia", "word blindness" and other words to describe many different
conditions related to reading disorders. Some used the term very broadly,
while others used a strict or narrow definition. Because of the confusion,
many investigators even refused to acknowledge the existence of the term;
they coined new phrases and used broader terms like "reading disorders"
to refer to dyslexic conditions.
Progress in reading research suffered tremendously from this
confusion. Vast amounts of data where collected which proved to be of little
use in advancing the knowledge of dyslexia. Differing testing methods,
experimental procedures, control groups, and research objectives were due
in large part to different interpretations of dyslexia. And because the
early research varied so greatly, much of it was incomparable; one piece
of evidence could not be used as a stepping stone for further research.
As more knowledge accumulated, the term dyslexia began to
take on a more specific definition. Today educators generally agree that
there is a broad range of reading problems among schoolchildren for wich
specific causes have been identified. But there remains a smaller group
of children who have difficulty in learning to read, for no apparent reason.
These children are called dyslexic.
Another problem is the broad scope of the term dyslexia.
Since it refers to all reading problems of an undetermined nature, it is
unlikely that there is just one cause, and one type, of dyslexia. An examination
of the symptoms of dyslexia shows errors in a wide range of skills, from
identification of simple combinations of letters to comprehension and retention
of material that has been read. As the causes of dyslexia are identified
they will probably be eliminated from the category of dyslexia and termed
specific reading disorders. In this way, the term dyslexia should become
increasingly narrow in scope until there won't be a need for the term because
all causes of reading disorders will have been identified.
But until we know the how and why of dyslexia, educators
won't be sure that they are focusing their efforts in the right area, or
that they aren't wasting their time on a theory that isn't valid.
SYMPTOMS OF DYSLEXIA
Children who have trouble learning to read show a great diversity
of symptoms due to the complexity of the reading process. Even children
with dyslexia show marked differences among themselves. Their only uniform
characteristic is a reading level significantly below what one would expect
for their age and intellectual level.
This lag reading ability has usually been expressed as a
delay in time, such as two-year delay. For example, a fourth grader is
said to read at a second grade level. While this method of measurement
has been convenient, it is misleading: a two-year lag in reading ability
for a third grader is much more severe than a two-year lag for a tenth
grader, because the delay shows that the third grader learned few of the
skills involved in reading while the tenth grader mastered eight years
or 80% of the skills a tenth grader needs. So with each grade advancement,
the same two-year delay becomes proportionately less severe.
Surveys that apply the same time delay to children of different
developmental levels only confuse our understanding of dyslexia. For example,
surveys have shown that only 3% of third graders are delayed in reading
by two or more years, while 25% of ninth graders are delayed by the same
two or more years. But the two-year delay in younger children is much more
severe than in older children, so a comparison between the delay of third
graders and ninth graders based on an arbitrary figure is really not a
true comparison.
Some researchers have proposed using a ratio, such as reading
age divided by mental age, to assess reading ability. The use of such a
ratio would be more accurate and helpful in comparing the reading delay
of children at different stages of development.
Because advanced reading abilities are based on the acquisition
of more elementary abilities, dyslexic children are likely to exhibit different
symptoms at various stages of development. For example, the younger dyslexic,
who is just beginning to learn to read, usually has trouble recognizing
or decoding words and simple phrases. The older child may have mastered
this level of development, but finds it hard to comprehend or remember
what was read. An older child retarded at a more elementary level can still
have difficulty decoding words as well as understanding what is read.
Samuel T. Orton, M.D., one of the first major researchers
in the area of dyslexia, identified the dyslexic errors which are most
widely known today. These errors include reversals in reading (b for d
and tar for rat) and the omission or addition of entire words. Orton also
studied the unusually high number of dyslexics who were left handed or
ambidextrous, or had trouble differentiating between right and left. This
research formed the basis of the theory that a neurological dysfunction
might be a cause of dyslexia.
Today most investigators agree that only difficulty in right
left orientation is significant. Many studies have shown that right-handed
children are not free from dyslexia and that many left-handed children
are normal readers. But difficulty in distinguishing between left and right
still intrigues many researchers, perhaps because of the left to right
orientation involved in reading English.
Another common symptom is faulty reading of vowels and consonants.
Dyslexics misread vowels more often that consonants, and consonants that
appear at the end of a word more often than consonants at the beginning
of a word.
Other symptoms are a slow (word-by-word) reading rate and
poor comprehension and retention of read material.
Some researchers have categorized these errors into two groups:
auditory
problems are difficulties in understanding the sound value of letters and
their combinations (confusion of vowel sounds and substitution of one consonant
for another); visual problems are errors of reversal and poor visual
discrimination between words of similar shape.
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