Studys and Considerations in Developmental Dyslexia of the Visual 
Subtype

Claire DeCapua

	The Parameters of investigation of reading disability have 
been drawn differently depending on the investigators. An example 
of this is the use of the term dyslexia by professionals in the 
field of medicine, neuropsychology and psychology.  However, 
educators in America study reading problems from the vantage point 
of a broader category called learning disability.    
	Dyslexia comes from the Latin prefix dys meaning inadequate, 
and lexia meaning lexicon or "words of the language".Most 
neurologists agree on the differentiation of acquired dyslexia or 
the alexias vs. developmental dyslexia until he sustained an 
insult to the brain i.e. a stroke, which may have damaged the 
language processing area.  The Alexias will not be covered in this 
paper due to the breadth of the subject matter.  Developmental 
dyslexia pertains to those individuals who have great difficulty 
learning to read despite having been given educational, and 
cultural opportunity. Consequently, in most studies of dyslexia, 
those subjects accepted for participation must 1) demonstrate an 
adequate I.Q. 2) demonstrate a lag behind classmates in reading 
achievement 3) adequate support at home with cultural exposure, 
and consistent school attendance. 
	Even though some dyslexic symptoms extend into adulthood, a 
large school district in Washington state, comprised of 10,000 
children, had success in educating children with dyslexia when the 
diagnosis was made early and specialized tutorial was administered 
in follow up.  The following percentages of remediation exemplify 
how crucial early diagnosis is.  There was 82% recovery from 
significant disability when the diagnosis was made in first or 
second grade.  When diagnosis was made in the third grade 
successful remediation dropped off to 46% if diagnosis was made in 
the fourth grade. The rate drops to ten and fifteen percent when 
the diagnosis was made in the fifth-seventh grade. 
	Due to the foregoing statistics the following approach of 
some educators is problematic.  Rawson (81) avoids the term 
dyslexia, and refers to these children as "language different". 
She teaches counselors and educators to look for potential 
advantages in the cognitive profile of poor readers, and to search 
out their special talents in spatial, inventive, and artistic 
abilities.  The problem with the above strategy is that for 
dyslexics who are language proficient, they may go undiagnosed 
beyond the crucial period when intervention might have been 
optimally effective. The child with a low I.Q., who requires a 
much slower and more structured instruction program may be 
misdiagnosed as "language different". However, to her credit, 
Rawson advises a comprehensive appraisal of the entire battery of 
test results, and symptoms, avoiding single indicators to identify 
the problems. 
	Experts investigating the etiology of dyslexia, approach the 
subject from different theoretical frameworks.  The unitary 
approach is accepted by those who believe that there is only one 
dysfunction that differs only in degree of impairment between 
individuals. It is thought this one particular deficit slows or 
distorts symbolic processing, making learning to read or spell 
difficult.  The second approach to analyzing the problem is 
advanced by those who believe that either Left Hemisphere language 
processing is disrupted resulting in a low verbal I.Q. or Right 
Hemisphere processing is disordered alone the path ways to the 
lexicon which would be demonstrated by low scores in visual 
symbolic skills.  The results of either Left hemisphere or Right 
Hemisphere processing problems is poor cross hemisphere 
communication. 
	The process of Left Hemisphere and Right Hemisphere 
processing and transfer of information will be handled below. 
Laterality in simplest terms is our ability to distinguish right 
from left. In its more complicated applications our brain is asked 
to distinguish left vs. right body images, asymmetrical object 
presented in mirror image, and letters and words that contain 
reverse counterparts i.e. d and b.  Researchers (Belmont and Birch 
in 1965) found a connection between inability to distinguish left 
from right cerebral lateralization, and severe dyslexia. 
Paradoxically the author warns that many disabled readers 
demonstrate no abnormality in left right differentiation while 
many competent readers show a typical brain lateralization.
	Although most preschoolers have attained binocular processing 
skills automatically, there can be a deficit in this skill for 
some children entering first grade that is attributed to 
maturational lag and or inexperience with the written language. 
Confusion with laterality usually clears up after the first year 
of schooling incorporating reading and writing.  Problems in 
visual perception can be evidenced in reversals of letters, words 
within sentences or entire passages.  When full texts of reading 
or writing is reversed this is called mirror image reading.  
Kindergarten teachers expect to see some reversal in their 
beginning students and clinicians see reversals in a low 
percentage of learning disabled. An adult dyslexic may reverse a 
syllable in a word, which is so subtle that is would be 
undetected.  Eye specialists who see patients with this problem 
often hear from the patient that they believe this condition can 
be corrected by prescriptive lenses. Many lay persons believe the 
above disorder is synonymous with dyslexia, however it is only one 
small subtype if seen in more advance readers.  If noticed in a 
beginning reader, it should be considered that perhaps they have 
not yet learned the rule of proceeding from left to right in 
printed English.
	Bilateral asymmetries do not present a hurdle if one is 
looking at a large object or an object at some distance.  However 
in reading, words most be seen close up and they are not 
symmetrical.  The fusion system of the human visual process 
tolerates a 5 degree inadequacy for ordinary stereopsis, but only 
1/4 degree of inaccuracy can be accommodate in fusing the images 
of fine print. When we first learned to read our visual system, if 
functioning normally, transfers a pattern of words and letters 
that reach the retina from the Right Hemisphere to the Left 
Hemisphere through the commissaries. It is in the Left Hemisphere 
where  decisions  re?? the meaning are made.  as we make progress 
in learning,  The Left Hemisphere teaches the Right Hemisphere 
sufficient knowledge of shapes of letters and words, which 
eventually results in the reader reading by sight and not needing 
to process each word retinopically.
	In work done by Stein and Fowler it was demonstrated that to 
avoid a confusing image eye positioning was important.  For the 
perceptual system to compensate for mirror image effects at 
commissural transfer the left hemisphere must receive information 
reposition of the eye at fixation.
	Stein and Fowler hypothesized a model to demonstrate pathways 
of binocular perception.  As an example, the image of a word would 
be received in the right visual friend (RVF) of both eyes. Twelve 
letters would be viewed to the right of the fixation, and 3-4 
letters would be viewed to the left. The image would then be 
transferred across the optic chasm and received in the left 
hemisphere. In the LH the word back is located and grapheme 
phoneme associations are made. The individual with right eye 
dominance and left hemisphere dominant for language will probably 
process print without problems caused by binocular vision. 
	When a word is seen in the Left Visual Field (LVF), the 
impression arrives reversed to the right visual cortex, via 
hemispheric transfer from both eyes. With Homotopic connections 
across the hemispheres there is compensation and a reversing of 
the image occurs from the right hemisphere. This results in both 
images of d, arriving at the right visual cortex as b, and are 
corrected to the original orientation. Stein and Fowler 
hypothesized this to be due to homotopic commissural relays in the 
angular gyrus.
	The angular gyrus receives messages from the occipital visual 
areas and from the eye movement control centers in the superior 
colliculus. The angular gyrus sends projections to motor control 
areas in the frontal eye fields, to the cer Lellum, and to 
Wernickes area for speech interpretation in the temporal lobe. One 
function of the angular gyrus is to unite signals from both 
retinae, in addition to eye position from the eye movement control 
centers located in the superior culluiculus. 
	Inherent in inter hemispheric transfer is the potential for 
confusion, which does not occur if real life interpretation of 
words can be established. In the model posited by Stein and Fowler 
the parietal lobe receives signals about eye movement in the 
opposite half of the visual space. As an example, if the right eye 
moves to the right, messages re; this eye position are sent to 
control centers in the left hemisphere. Simultaneously retinopic 
messages stay the right hemisphere. In this predicament, a letter 
viewed in the left visual field is projected to the right 
hemisphere, where it can be seen but not interpreted. Also its 
position will not be known because this information is the 
function of the Left Hemisphere. The authors believe eye position 
control to be essential in early stages of acquiring reading 
skills.
EYE DOMINANCE AND MONOCULAR OCCLUSION
The tendency for one eye to be used more then the other in vision 
is termed monocular preference. The average person exhibiting this 
monocular preference would be right dominant for seeing, 
listening, and walking with dominant control in the left 
hemisphere. When left and right preference is mixed, this is 
termed mixed dominance. In disabled readers the rate of crossed 
eyeness, and handedness is higher then in the general population. 
The stronger eye is usually dominant, but less frequently the 
weaker eye is. Monocular preference is believed to be established 
in early in fancy and possibly before birth. Goldman,Shiffman, and 
Bender in 1983 pose it the claim that right hand preference is 
associated with left cerebral dominance. They do not accept the 
view that lateral dominance or poorly defined laterality corrality 
correlates with reading disorder.
	Orton in 1937 did pioneering work in hemispheric dominance. 
As an outgrowth of his work, the link between laterality and 
visual function was ought by Dunlop. Dunlop and Fenelon. Below is 
described the "reference eye test". The participant is directed to 
look down two tubes in an apparatus called a synoptophere. Each 
eye is viewing two separately but similar slides. In both slides 
there is a center front door, and the participant is asked to 
fixate on the center of the door. One slide contains a small tree 
to the left of the front door, and in the other slide there is a 
larger tree to the right of the door.The tubes are manipulated by 
the examiner so that they converge, and the participant has the 
impression of a fused image of a single house with a tree on 
either side of the door, in the center 2-3 degrees of binocular 
vision.
	In the second part of the experiment the tubes are made to 
diverge, and if this occurs slowly and smoothly most participants 
receive the perception that one of the trees moves towards the 
door. Fusion then breaks down and two separate images can 
berdetected??? At this point, in both slides the position of the 
tree and door clearly remain fixed in relation to each other. 
However when the tubes diverged the neural signals responsible for 
monitoring eye movements and eye position indicate that the eyes 
are no longer in a position, consistent with looking at the same 
object. Nevertheless the image on each fovea is still largely the 
same. Because of this situation, there is disparity between 
retinal and extra-retinal signals. 
BRIEF VISUAL DISPLAY TESTING 
In resolving this disparity the perception of movement occurs. The 
dominant or reference eye is identified as the one whose image 
remains static..Dunlop, Dunlop and Fenelon (1973) studied 15 
dyslexics and 15 non disabled readers using the above described 
procedure and found that crossed reference, i.e. a reference eye 
on the opposite side of the preferred hand was associated with 
reading retardation. The retarded readers also had a higher 
incidence of convergence deficiency, defective stereopsis, and 
esophoria. Their hypothesis based on the above is that failure to 
develop an appropriate reference eye leads to perceptual problems 
that disrupt reading.
	Stein and Fowler found unfixed dominance in 60% of their 
visual dyslexics and only in one of 80 normal reading subjects. 
The Dunlop test was used to detect" disorganized fixation during 
convergence," "failure of hemispheric dominance" and unstable eye 
position. To be certain that input would go to the left hemisphere 
where they assumed language meaning was stored they patched the 
left eye. The dyslexics treated in above fashion gained 13 months 
in reading progress during the 6 month experiment, while non 
treated dyslexics gained four. One group of critics of this study 
stated that the patches children wore flagged them as experimental 
and may have inadvertently facilitated their getting extra help. 
Consequently the study was replicated with all dyslexic children 
wearing glasses. Half of the children wearing glasses were chosen 
to have one lens occluded and the other half of the participants 
wore lens with no occlusion. After a 6 month treatment period, 51% 
of the subjects wearing occluded lenses had converted to fixed 
reference vision, while only 24% of the untreated subjects 
converted. The treated group advanced 6 months in reading 
achievement while the untreated group regressed 4 months. The 
author of the study conclude that the dyslexics who received 
treatment but did not improve were found to have phonic and 
sequencing errors. They caution that fine binocular vision deficit 
is not the only cause of dyslexia.
	In his paper Reading Retardation, Charles Hulme criticizes 
the above study for several reasons. He points out that of the 
group of participants who had no reference eye or the unfixed 
group, 60% received the occluded spectacles. While those with a 
fixed reference eye, 28% received spectacles. He points out this 
seem unreasonable on the basis of the claim of the authors that 
subjects were chosen randomly. Another criticism he has of the 
study is that the authors of the study do not inform us of 
important characteristics of these children i.e. ages, reading 
ages, and I.Q. In addition he also points out that in the 6 month 
follow up study done to as certain which children maintained or 
continued to progress in reading ability after they had attained 
ocular dominance, reading score in the group that converted 
increased 11.6 months over 6 months. In the group of participants 
who remained without a faxed reference eye, 50% improved in 
reading scores by 5.6 months over the 6 month period. He 
interprets this to signify that it is not unambiguous that the 
occlusion was responsible for the improvement of reading 
performance.
	Another flaw in the study as critiqued by Hulme is the use of 
one test, the Dunlop, which showed improvement, as they responded 
consistently in the reference eye test, and they had further 
increases on the reading test, which was a separate measure. He 
conjectures that perhaps this group of participants simply learns 
better then the other group. Additionally they may have differed 
in other significant characteristics, i.e. age, I.Q. and reading 
level before they began.
	Stein and Fowler tried to counter the above argument by a 
reanalysis of two groups of children matched for degree of initial 
reading retardation and I.Q.. One group was given plain spectacles 
and remained unfixed and the other group was given occluded 
spectacles and converted. In this group the claims are even 
greater for improvement in the reading scores. Again Hulme points 
out the disparity due to the fact that the children were 
originally selected using one test and then compared using a 
different measure. He ultimately points out two subsequent studies 
which fail to confirm similar findings, one done by Bishop Jancey 
and Steel in 1979 and another done by Newman in 1985.
	Concludes that oscular dominance is rare, and that it would 
require additional studies to substantiate the claim that it is 
linked to retarded reading. If it ever is linked, his opinion is 
that it will be the case for a minority of retarded readers.
BRIEF VISUAL DISPLAY TESTING 
	Lyle and Goyen (1975) conducted studies to test the 
hypothesis that retarded readers problem lays in the inability to 
deal with rapid visual displays. Thy presented abstract shapes via 
a techistoscope to impaired and non impaired readers. The impaired 
readers were less accurate in making poseurs. Both groups of 
readers were similarly affected when the discrimination was 
manipulated by the examiner so that it was more difficult to make. 
Both groups tested similarly when the exposure time was 
lengthened.
	Two different methods of testing to examine this in more 
depth have been constructed. in one technique called backward 
masking a stimulus is presented briefly, which requires 
identification. Next a second stimulus is presented which is 
called the interfering stimulus or the mask. The results of these 
tests showed that impaired readers required a longer length of 
time between the presentation of the two stimuli. The second 
testing strategy involved comparing the time interval between 
stimuli required for separation to occur gives the examiner an 
index of visual persistence, i.e.j the length of time the first 
stimulus remains visible. It was found through this type of 
testing that the impaired readers exhibited longer visual 
persistence, but it has been hypothesized that this is only true 
when the stimulation of the same retinal areas occurs. 
	To test the hypothesis that impaired readers have longer 
visual persistence when stimulation occurs at the dame retinal 
area DiLollo, Hanson and McIntyre in 1983 demonstrated that 
impaired readers needed longer intervals between the target and 
the mask in 2 separate studies. Impaired readers needed a longer 
interval to detect separation between two successive straight 
lines presented in the same location. No difference in time 
interval was noted in the ability to maintain an image of matrix 
formed by successively displayed dots when they fell on different 
retinal location. 
	The above researchers suggested from their studies that the 
impaired reader suffers from slow information processing. Hulme 
posits that there is insufficient evidence for this. In the study 
where impaired readers were compared with non impaired, the 
children were chosen at the same age level, however, differences 
in reading ability and experience could account for their 
findings. Difficulty with rapid displays has been noted in 
mentally retarded children. Visual persistence decreases with age 
even in normal subjects, which makes it likely that these results 
can be accounted for by an immature nervous system or an 
inefficient central nervous system.  impaired readers are more 
likely then normals to show signs of minor neurological damage or 
immaturity. Hulme continues that the differences in visual 
processing described above may be the result of CNS immaturity, 
and may not be the cause of reading impairment.   
    
References:

Cognitive approaches to reading, Beech J. and Colley, A. (1987)
 New York :John Wiley & Sons.

Psychology of reading, Pobeck, M. and Wallace, R. (1990), 
Hilldale, N.J.: Eribaum and Assoc.

Copyright © 1999, Dr. John M. Morgan, All rights reserved - This page last edited 13 - December, 1999
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Mildred, C. Robeck Psychology of Reading. Ed. Randall R. Wallace Erlbaum Associates Hilldale, New Jersey 1990. pg. 261. Mildred, C. Robeck Psychology of Reading. Ed. Randall R. Wallace Erlbaum Associates Hilldale, New Jersey 1990. pg. 260.