45th Annual Conference of the International Military Testing Association
Pensacola, Florida, 3-6 November 2003
Study A11. Pages 96-102


Susann L. Krouse
Naval Education and Training
Professional Development and Technology Center Pensacola, FL, USA

James H. Irvine
Naval Air Warfare Center, Weapons Division
China Lake, CA, USA
Perceptual dyslexia—also known as Irlen Syndrome, Scotopic Sensitivity Syndrome, SSS, scotopic sensitivity/Irlen syndrome, and, in the United Kingdom, Meares-Irlen Syndrome—is a perceptual disorder that affects an estimated 46-50 percent of those with learning disabilities or reading problems; 33 percent of those with dyslexia, attention deficit (hyperactivity) disorder, and other behavior problems; and approximately 12-14 percent of the general population (Irlen, 1999). It is not a dysfunction of the physical process of sight. People with perceptual dyslexia can have 20/20 vision or they may wear corrective lenses. Perceptual dyslexia is a problem with how one’s nervous system encodes and decodes visual information and transmits it to the visual cortex of the brain (Warkentin & Morren, 1990).


People who are affected with perceptual dyslexia have problems accommodating specific wavelengths of light, and each person’s troublesome frequency is unique. Factors such as bright light, fluorescent light, high-gloss paper, and black-and-white contrast can aggravate the disorder. The victim’s scope of focus may be restricted so that he or she may only see very small bits of a line of text instead of the entire line. The text that the person sees might blur, swirl, move, pulsate, vibrate, or even disappear. The white page is too bright; or it may flicker or flash; or colors may appear. SSS victims rarely report these symptoms to others because they think that everyone experiences the same problems (Irlen, 1991). Those with perceptual dyslexia often avoid reading at all costs, and, as a result, they may be affected physically, academically, and psychologically (Irlen, 1991).

From a physical standpoint, because of the text distortions suffered, reading becomes extremely difficult, often physically painful. Without intervention, victims of Irlen Syndrome exhibit symptoms such as sensitivity to light, headaches, nausea, eyestrain, sleepiness while reading, attention deficit, and distortions of text (Irlen, 1991).

Academically, everything derives from reading, and victims of Irlen Syndrome invariably find it difficult to read. They may skip words or reverse or change letter order—seeing the word “saw” as “was,” for instance. They may have poor penmanship, a result of difficulty with spatial orientation: they misjudge how much space to leave between a pair of letters or words. Because they frequently can’t envision an entire word, they find it difficult to spell or work with large numbers (Irlen, 1991).

Psychologically, the victim of perceptual dyslexia is prone to exhibit problems with behavior, motivation, and self-esteem. Those with SSS frequently exhibit symptoms of attention deficit disorder, acting out, and behavior problems (Irlen, 1991). They are often poorly motivated to succeed. Almost invariably they tried early on, when they were young. But with few successes and many “failures,” their attitude became “why bother?” Their selfesteem is low because, while everyone around them is reading and learning, they cannot—no matter what they do or how hard they work, they just can’t seem to “get it.”

Identification of SSS

Helen Irlen, a literacy instructor in California, first identified this perceptual dyslexia in the early 1980s and labeled it “scotopic sensitivity syndrome.” Irlen had received a grant from California State University, Long Beach, in 1980, to set up a literacy program for adults. She chose to work with adults because adults can communicate better than children and are more accurate “reporters” of what they experience; they are less intimidated by authority than children and are less likely to he swayed without some evidence; and adults are more motivated to succeed. They have reached a point in their lives where they recognize the importance of learning in general and reading in particular.

After three years of in-depth research, Irlen discovered that many problems appeared after readers had been actively reading for a relatively short period of time (usually about 10 minutes or more). Those who had trouble reported that distortions began to appear on the page, and those distortions prevented them from comprehending the words. All of their energy was going into perceiving the words, holding them on the page, or even just finding them! As a result, many stopped reading. It was just too difficult for them. As Irlen explained in her speech at the dyslexia Higher Education Conference, October 31-November 2, 1994, at Plymouth University, England, once she began asking the more definitive question, “WHAT do you see?” instead of “DO you see?” the answers made it apparent to her that these poor readers were victims of a unique syndrome that was not being adequately addressed by the professional educational community. (Dyslexia in higher education: strategies and the value of asking).

Serendipitous Discovery

One day, one of Irlen’s students discovered that when she placed a red overlay—left over from previous eye-dominance exercises—on the page she was reading, the sensation of movement that she had always experienced stopped! For the first time, she could actually read without having the words constantly sway back and forth! (Irlen, 1991) The red didn’t work for everybody, however. It made no difference to the rest of the students.

So, Irlen tried other colors and found that the vast majority of those who tried the colored overlays were helped. Each person who was helped responded to one specific color. Once that particular color was determined and used, the individual was able to read better and longer and reported that the distortions previously experienced disappeared immediately. Irlen didn’t know at that time why the overlays worked, just that they did.


With the advent of magnetic resonance imaging, we’ve been able to determine that the brains of all dyslexics—including perceptual dyslexics—work differently than those of non-dyslexics. (Lewine, et al., in press) Dyslexics use a different part of the brain than nondyslexics when they read, and they use a larger portion of their brain when they read or perform visual tasks.

Receptor Field Theory

In the 1980s, visual physiologists developed the receptor field theory of color vision. This theory hypothesizes that the cones of the eyes are organized into eight sets of concentric, counterbalancing fields. Cones, of course, help us distinguish things clearly and distinctly. Because they contain photopigments that are sensitive to red, green, and blue light wavelengths, we are able to see color. (Irvine, 2001)

Each type of field is determined by the field’s color region arrangement and the balance of the output of each field’s energy or signal. The output should be equal—that is, neither positive nor negative—as it passes through the optic nerve to enter the brain’s visual processing center. (Irvine, 2001)

If the receptor fields are summed to a unity as they enter the brain’s processing center, and each single receptor field is equal to the others (so that none is governing or dominant), there will be no perceptual distortion, and the image formed will be accurate. On the other hand, if any of the receptor fields does not sum to a unity or is, in fact, dominant under a set of spectral input conditions, the visual control system will change, and the image formed will overlap, swirl, jump about—generally be distorted. (Irvine, 2001)

The Pathways to the Visual Cortex

Over the years since Irlen’s discovery, numerous studies of this visuo-perceptual disorder have been conducted, and the general consensus is that scotopic sensitivity syndrome affects the way the visual pathways carry messages from the eye to the brain.

There are two pathways to the visual cortex:


  • the magnocellular, which does fast processing of information for perceiving position, motion, shape, and low contrast; and
  • the parvocellular, which carries out slower processes for perceiving still images, color, detail, and high contrast.



It is theorized that when the receptor fields do not sum to unity, the pathways are affected, causing the magnocellular impulses to be slowed, so only partial perception occurs. This results in words that blur, fuse, or seem to jump off the page (Newman, 1998). Individualized colored filters seem to return the balance between the two processing systems, preventing this overlapping (Robinson, 1994). The colored overlays and filters cut down or eliminate the perceptual problem by screening out the wavelengths of light troublesome to the individual (Sims, 1999). Studies of both the long- and short-term efficacy of the transparencies and filters have shown that they do, indeed, provide benefits to the individual afflicted with SSS (Whiting, Robinson, & Parrott, 1990; Robinson & Conway, 1990).


Although there have been numerous studies into perceptual dyslexia since its recognition in 1983, we will look at just three in this paper: Irvine, Lewine, and Wilkins.

Irvine’s Experiment for the Navy

The Navy wanted to see if the visual performance of those afflicted with perceptual dyslexia changed as the energy spectrum presented to them changed. Therefore, in 1995, James Irvine conducted an experiment at China Lake, California, that showed that for certain perceptual dyslexics the receptor fields do NOT sum to unity, so the image sent to the brain is not crisp and clear. When this happens, the subject’s visual control system alters radically, so the subject does not see the image properly. (Irvine & Irvine, 1997)

Lewine’s Study

In the late 1990s, Dr. Jeffrey Lewine, a neuroscientist then at the University of Utah Center for Advanced Medical Technologies, discovered that modifying the light frequency spectrum that went to a perceptual dyslexic’s vision system could make the brain alter and revert to a more normal brain pattern. He also noted that he could actually cause five to six percent of the “normal” population to develop dyslexic-type dysfunction when they were exposed to “abnormal” light frequency environments. (Lewine, et al., in press) This means that some ordinarily non-dyslexic personnel can develop gross inefficiency, degraded performance, and/or become dysfunctional and unable to perform normally under certain lighting conditions such as red battle lighting, blue precision operating bays, or in foggy or hazy conditions.

Wilkins’ Studies

Professor Arnold Wilkins, while a research scientist at the Medical Research Council Applied Psychology Unit of Cambridge University in the United Kingdom, studied the neuropsychology of vision, reading and color, photosensitive epilepsy, and attention, conducting double-blind experiments to validate the existence and potential treatment of perceptual dyslexia. He did this using four different groups of readers, mostly children, randomizing the presentation order of the overlays, and further randomizing the use of the appropriate overlays versus placebo overlays. (Wilkins, 2003)

Wilkins’ studies determined that, when given the choice, about half the readers would choose clear overlays, and the other half would choose the colored overlays. Given that only approximately 15 percent of the population is afflicted with perceptual dyslexia, we can assume from Wilkins’ experiments that, in addition to these people being helped by the colored overlays or filters, some of those not-so-afflicted can also benefit from color!


Generally speaking, before we can treat perceptual dyslexics, we have to identify them.

Types of Screening

There are generally three types of screening that would be used, two of which are based on the Irlen Method:


  • In the field or at the recruiting site, a simple, 10- to 15-question inquiry of the subject, and trial-and-error determination of the appropriate colored overlay.
  • At the Recruit Training Center or a major command, an in-depth inquiry consisting of questions concerning the subject’s symptoms and related history.



The third test, the Wilkins Rate of Reading Test, is also easy to administer and consists of four easy one-minute tests. The entire process should not take more than about a half hour.

Resources Required

There are many ways to improve the situation for perceptual dyslexics without having to spend a penny. Such simple and cost-free actions as dimming the lights in a room, using natural instead of fluorescent lighting, allowing students to use colored paper and to wear caps or visors indoors, and avoiding the use of white boards will all help. (Irlen, undated; Wilkins, 2003)

But to alleviate the problem requires intervention in the form screening and, ultimately, selection of appropriate colored overlays or filters. The outlay required to implement such a program would be minimal. Only basic instructions would be required at the recruiting sites, enough training for the recruiter to be able to administer the simple Irlen Type-1 test or the Wilkins Rate of Reading test and to assist the applicant in choosing the appropriate overlay. At the Recruit Training Center, it is anticipated that one or two Educational Specialists who have backgrounds in education and have been trained in the Irlen Method will be required to administer the screening and perform the diagnostic analysis.

Supplies of overlays or transparencies for recruiting sites and the Recruit Training Center will also be necessary. Overlays from Irlen Institute cost approximately $1.25 each, although less expensive transparencies are available from other commercial sources. (It must be remembered, however, that Irlen overlays are specifically designed and developed for the purpose of alleviating SSS.) Tinting of lenses (whether corrective or not) adds about $50 to $100 per pair at this point in time. Under contract, however, the price will certainly drop to a more nominal figure (Irvine, 1997).


And what will we get back for this investment? The individual service members will benefit, of course, with improved reading speed and comprehension. Because they will experience less visual fatigue, their attention spans will increase. As they begin to understand and realize that they can do what they thought they couldn’t do, their self confidence will improve, as will their attitude to training and the job itself. Just knowing that there is a solution available will often be enough to change an attitude and strengthen a resolve to succeed.

The military services will also reap the rewards of this program because, in addition to increasing the qualified pool of applicants for enlistment, the young people affected will be able to train more efficiently. Remediation, basic, and ongoing training will be more effective and, as a result, more efficient. With more effective training, the service member will be more knowledgeable and efficient in the field. It can further be anticipated that there will be fewer behavioral problems—both during and after training—primarily due to the change in attitude that has been shown to occur following screening and diagnosis for SSS.

All in all, we believe that a higher-quality service member will be delivered to the field or fleet, both academically and attitudinally.


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