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Theories of Dyslexia – An Evolution in Thinking


By Dr. Donna

From Visual Sources of Dyslexia to Language Processing

While the cause of dyslexia in a child are generally related to language processing delays, this wasn’t always the thinking.  Since learning how to read was reserved only for the elite for many centuries, theories on the cause of dyslexia are relatively new. Without tens of thousands of people reading up until the 1900s, there was less opportunity for cases of dyslexia to appear.

Unlike medical conditions such as infections, where protocols were available since before Hippocrates’ time, dyslexia wasn’t discovered until almost 1900 and its treatment didn’t start until decades later.

There are three primary theories of dyslexia and what causes it:  visual, language and cognitive. Each of these appeared to be valid in their own time.

The Visual Defect Theory

The first case of someone with dyslexia wasn’t reported until 1896 when the British doctor, W. Pringle Morgan, described a 14-year-old boy who couldn’t learn to read. Despite the reading problem, he was doing quite well in other subjects. Morgan’s theory was that there was a deficit in storing visual representations of the words that were being read.

During this time, the existence of medical journals made medical matters a talking point between various physicians. The term “word blindness” was coined by a Scottish optic surgeon, James Hinshelwood, and announced to the medical world in The Lancet in 1896. One article led to the next, and soon a complete collection of articles opened the door to British ophthalmologists learning about dyslexia. By 1917, Hinshelwood’s theory was refined: dyslexia was inherited. It was found more often in boys and was remediable.

Just because there was a genetic part of the dyslexia puzzle, it didn’t mean that the visual theory disappeared. In 1925, the neurologist Samuel T. Orton, American neurologist and psychiatrist, released a paper about his “twisted symbols” theory. This theory focused on how ambidextrous children had a higher tendency to reverse and transpose letters. After studying close to 3,000 children, he concluded that they had deficient visual perception of letters. It was thought that these were perhaps due to a brain malfunction in the hemisphere dominance of one occipital lobe over the other. Many people still believe that the primary definition of dyslexia is the reversal of letters, although the definition of dyslexia has progressed to mean a lot more than this.

After Orton died in 1948, the Orton Dyslexic Society was created to improve the life of dyslexic children and adults. Special attention and learning centers were created and the Society stood up for the rights of those who had the learning difficulty.

Not a Visual System Deficit at All – or Is It?

In 1957, Alfred Tomatis in France proposed the idea that dyslexia was a problem of the auditory system, not the visual system. Tomatis created a method to reverse the deficits, but it never really caught on with those who needed it.

Throughout the 1960s, it was popularly believed that the cause of dyslexia was due to both auditory and visual deficits.

By 1970, if you had dyslexia in Great Britain, you were included in those considered disabled in Great Britain’s Chronically Sick and Disabled Persons Act.

The Cause of Dyslexia is A Delay In Language Processing

By the 1970s, imaging techniques were being created for the medical profession. In 1971, Isabelle Liberman, a psychology professor at the University of Connecticut used neuroimaging to determine that reversal errors in reading do not have to be visual in nature. She proposed a verbal / linguistic cause of dyslexia, which was supported by other researchers in the field.

By 1979, dyslexia research took on a new twist. Vellutino noted that dyslexics have difficulties establishing verbal associations and may not be able to decode words by phonemes. This means the difference between the word lip and rip couldn’t be heard. In normal readers, if there was a deficit in the ability to process these phonemes, there usually were deficits in short term memory, too. Thus, it was established that dyslexia was a language processing deficit, not a visual problem.

There was some merit to these new theories of dyslexia, although different languages have different complexities of phonological rules. Dyslexics seem to make more mistakes and are slower readers when the language is more complex phonologically.

Teaching methods were created to address these language deficits in Europe and used successfully for many years.

Cognitive Skill Delays That Cause Dyslexia

Language acquisition is part of linguistics, and scientists next took the idea a little farther and in a slightly different direction. Spring, Capps, Denckla and Rudel soon proved that just because a child was dyslexic, it didn’t mean that he or she didn’t have a good vocabulary; instead, the child was simply a little slow at naming colors, numbers, objects and letters. The cognitive abilities used to name objects had to be a necessary part of the puzzle.

With their research, it became obvious to all dyslexia investigators that everything related to reading skills had to be studied. The cognitive theory was born.

In 1975, the U.S. National Committee on Learning Disabilities was created. These experts suggested that learning disabilities subgroups should be studied to determine the cause of dyslexia, and the diagnosis and treatment of each subgroup. This meant that those with specific reading deficits could potentially be treated differently from those with other specific reading deficits. In 1976, reading disability was proven as a learning disability subgroup, identifying backward readers and those who were reading retarded.

Rapid Naming and Working Memory are Deficient

An example of how those with dyslexia have cognitive skill deficits is the inability of dyslexics to find words accurately and quickly. This skill is called rapid naming. Scientists discovered that rapid naming skills are a precursor of reading deficits.

On a similar note, accuracy and speed of single word identification predicts reading ability. Researchers at the University of Toronto found that without the ability to identify single words quickly, efficient reading wasn’t possible. It was reasoned that if dyslexics have a word recognition deficit, then this affects their reading comprehension, vocabulary and eventually intelligence.

And since children with dyslexia struggle to process information rapidly, these cognitive deficits may cause the phonological deficits, proposed the scientists in 1995. Maybe the cause was one of rapid information processing.

Another cognitive deficit found in dyslexics was working memory capacity. The inability to hold words in memory could lead to coding deficits, although some experts suggested that the memory banks were small only for language information. Regardless of the theory, it was possible that if ways to increase working memory were initiated, maybe dyslexia could be remedied.

During the 1980s, the most prominent theories were primarily that dyslexics had phonological skill and isolated word recognition deficits. They are slower at rhyming as well.

New Direction for Researchers Still Hunting for the Source

The 1990s and later years, the theories of dyslexia have become settled science.  Reading is a language skill, and dyslexia is caused by difficulties processing language, phonological and other delays.

These days scientists have started looking for the source of these language processing delays.  Is there a  genetic basis for dyslexia?  So far a relationship between chromosomes 6 and 15 and reading disability have been confirmed by some researchers and disputed by others.

Or is there an environmental factor?  Studies show strong links between the number of words a child hears in early life and reading ability later on, but are there other environmental factors?

And yet, despite all these theories, everyone agrees on one thing:  dyslexia can be remediated. And that alone is enough reason for hope.

The next step is to create a plan for treating the dyslexia. Find the dyslexia treatment that’s right for your child at Gemm Learning.

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