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Dyslexia (Reading Disorder)

The word dyslexia has two different meanings in popular usage:

  1. difficulty decoding written language into sound (inability to read fluently aloud)
  2. difficulty extracting meaning from text (being unable to answer questions about what is read)

These problems interact. The most common cause of comprehension difficulties (definition #2) is difficulty in phonological encoding (definition #1). Struggling to sound out words pulls cognitive resources away from comprehension.

The two processes (sounding out words and arriving at compre­hension) are different, however. Some people are perfectly fluent at reading aloud but have very limited comprehension of what they read. That is a feature of hyperlexia, a disorder sometimes accompanied by autism-like symptoms.

Dyslexia researchers usually use definition #1, because phonological encoding is the problem affecting most dyslexics. Researchers therefore study the processes that enable fluent reading (ability to read aloud).

Students and teachers using the term dyslexia are usually referring to definition #2. They are concerned with a student's ability to understand what is read. It does little good to be able to say words aloud if they are not comprehended.

Critics of definition #2 point out there is no firm line between dyslexia as a biological syndrome and effects of poor instruction or lack of practice. Reading is not a natural ability; it must be taught.

Consequently, a reading disorder is ambiguous: it might be due to some biological problem, or it might be due to poor instruction or lack of experience. Dyslexia is usually defined as a reading problem that persists despite "normal intelligence and adequate schooling."

Another problem with definition #2 is that it could involve so many different problems. Reading was described in Chapter 7 (Cognition) as an interaction of structural, lexical, and phonetic levels.

"Structural" refers to how sentences and larger idea units are put together. "Lexical" refers to vocabulary. "Phonetic" is about word attack. Reading involves all those skills interacting in real time.

Anything that disrupts the long series of information processing steps between perceiving letters and comprehending the meaning of a passage can produce a reading disorder. Researchers have examined a wide variety of factors:

–problems in verbal short term memory

–visual sequencing difficulties (reading "was" as "saw")

–unstable representation of sounds

–stable representation of sounds but difficulty accessing them

–using visual mental representations rather than abstract verbal strategies

–a deficit in visual sampling when scanning letters

–less knowledge about how to approach reading (metacognitive problems)

–slower retrieval of word meanings (lexical retrieval)

–problems with rapidly presented stimuli, either visual or auditory (the "temporal processing hypothesis")

–a problem converting spatial arrays (e.g., spelling patterns) to temporal form (e.g. word sounds)

With such a variety of problems that might cause reading difficulties, researchers are reluctant to equate dyslexia (traditionally associated with difficulties in sound decoding) with reading difficulties in general. DSM-5 stopped using the label dyslexia as a general label for reading disorders.

What is dyslexia called in DSM-5?

DSM-5 introduced a new category called specific learning disorders and included reading disorders in that category. This led to protests from the dyslexia community about the disorder being "dropped from DSM-5." However, DSM-5 included this language:

Dyslexia is an alternative term used to refer to a pattern of learning difficulties character­ized by problems with accurate or fluent word recognition, poor decoding, and poor spelling abilities. (p.67, DSM-5)

Research that compares dyslexic and non-dyslexic brains is common, and differences are usually found. Tamboer, Vorst, Ghebreab and Scholte (2016) examined bran scans of students who were diagnosed as dyslexic or not, using a machine learning algorithm to look for differences in the brain scans.

They found two areas where dyslexics had thicker gray matter and one area where they had less gray matter. After being trained on the sample scans, the machine learning algorithm was able to identify new scans as dyslexic or not with 80% accuracy. This indicates consistent brain differences between dyslexics and non-dyslexics.

Brain differences exist before formal school instruction (Norton, Beach, and Gabrieli, 2015). That suggests that the brain differences come first and have the effect of discouraging some students from practicing their reading. I.e. the brain differences are a cause and not an effect of reading troubles.

What is some evidence for brain differences in dyslexics?

Belgian researcher Bart Boets (2014) believes brain scanning evidence shows a problem in a particular path­way between the left frontal and temp­oral regions of the brain: the arcuate fasciculus. That is the fiber tract con­necting Broca's and Wernicke's areas.

A data-driven approach (looking for distinctive differences without regard to theory) found "connection problems" in dyslexic brains (Finn et al., 2014). Activity between key areas was less synchronized when reading, and in some cases dyslexics used different areas of the brain during reading than non-dyslexics.

About two-thirds of dyslexics have problems with phonological encoding. These are sometimes called verbal dyslexics. When the word dyslexic is used by itself, researchers are usually referring to this group: the two-thirds of dyslexics with the phonological encoding problems (definition #1).

Their problem involves translating from perception of letters to the sound of a word. Most dyslexics can perform this translation, but only slowly, which harms comprehension.

Boets et al. (2013) used fMRI bran scans to study the response of dyslexics to word sounds. They found that dyslexics had correct "internal dictionaries" of word sounds, but "accessing the dictionary was more difficult than normal." Even a small delay is enough to reduce reading fluency and automaticity.

What are two different types of dyslexia?

The remaining third of dyslexics are visual/spatial dyslexics who have trouble discriminating the spatial relationships of letters in a word. This can also be called surface or orthographic dyslexia, so there are four different labels for this form of dyslexia.

These individuals tend to invert letters when young, turning them backwards or upside-down when they write. They also make left-right confusions when reading, confusing b's with p's, or reading "was" as "saw."

Researchers say this is a problem with organizing visual shapes or gestalts. It impairs whole-word recognition.

That, in turn, slows down visual/spatial dyslexics. Without a quick recognition response of whole words, the visual/spatial dyslexic must fall back on a slow sounding-out strategy, like those with phonological encoding problems.

How can spatial dyslexia be detected with a simple test?

Visual/spatial dyslexia might be diagnosed with a simple test. Dr. Martin F. Gardiner of the Harvard Medical School found that visual/spatial dyslexics have trouble tapping out a rhythm with their fingertips, given only verbal instruction.

For example, the instructions might be, "Tap three times quickly, then twice slowly, then five times quickly, then three times slowly." Can you do it?

"Anyone can tap a finger on a table," Gardiner said, "but the spatial dyslexic is unable to tap a rhythmic pattern in response to verbal instruction, even though the instruction is perfectly well understood." He said he had applied the test mainly to well-educated subjects who had lifelong reading difficulties.

They were often surprised by the results (Browne, 1988). "Those who had had reading difficulties through much of their lives, including a doctoral candidate, could not correctly obey the tapping instructions."

What simple test did Gardiner devise?

Why would a person who has trouble reading also have trouble following instructions to tap a rhythmic pattern with fingers? The common element in the two tasks is using words to guide a complex cognitive production. Perhaps that is a specific difficulty for visual/spatial dyslexics.

The common denominator in all forms of dyslexia, using definition #2, is difficulty arriving at an accurate final meaning when reading. A dyslexic student typically does poorly on tests that require verbal comprehension.

What sorts of compensations are possible?

There are ways to compensate for a reading disorder. Reading techniques themselves can be taught (as in our Chapter Zero). The sensory mode can be changed. For example, textbook chapters can be read onto tape by a volunteer, or a machine can be used to produce speech from text.

One dyslexic girl went from D grades to B grades simply by having a graduate assistant read quizzes to her. She could process the information if she heard it, but not if she read it.

She told me she survived high school by always discussing textbook material with friends so that she could hear it. She graduated with an undergraduate degree from our psychology depart­ment, and her experiences motivated her to obtain a Masters degree in Special Education.

With hard work and the support of others, plus acts of compensation such as hiring people to help with reading and writing, dyslexics can do well in professional life and achieve positions of prominence.

For example, Dr. Richard Wyatt, former director of adult psychiatry at the National Institute of Mental Health, had dyslexia and could barely read. "I've developed compensation strategies," Dr. Wyatt said. "It's the same as compensating for being deaf or blind."

As director of a research program, Dr. Wyatt survived by struggling over every paper he wrote. He employed an editor to correct his spelling and writing.

How did Richard Wyatt compensate for his dyslexia?

Wyatt also felt that his thought process was different from that of other people. "I think in a higgledypiggledy fashion," he said. His ideas "may be off the wall–and usually they are," he said. "But occasion­ally, I bring in something good." (Kolata, 1987)

Reading disorders are only one variety of learning disorder. Another category is dyscalculia, a problem with numbers or calculation. Like dyslexia, the term dyscalculia was retired in DSM-5, in favor of "specific learning disorder" sub­types for calculation and mathematical reasoning.

What are other learning disorders not covered here?

Not every cognitive disorder is listed in DSM-5 as a disorder. Some students have a specific problem learning a second language in adulthood. They just cannot seem to do it, despite trying hard and receiving competent instruction.

Similarly, some people cannot compre­hend or produce music. That could be regarded as a learning disorder. Clumsi­ness or lack of motor coordination could be regarded as a learning disorder.

DSM-5 limits the term learning disorder to "persistent difficulties in reading, writing, arithmetic, or mathematical reasoning skills during formal years of schooling." Problems of motor coord­ination are listed separately under the category of motor disorders which includes motor tics and Tourette's disorder.

From a cognitive or biological perspec­tive, the inability to carry a tune, or the inability to sketch or draw accurate pictures, is not much different from the inability to calculate or read fluently. All skills depend on specific brain areas, and nobody is good at everything. In that sense, everybody has some disabilities or learning disorders.


Boets, B. (2014) Dyslexia: reconciling controversies within an integrative developmental perspective. Trends in Cognitive Sciences, 18, 501-03. doi:

Boets, B., Op de Beeck, N.P., Vandermosten, M., Scott, S. K., Gillebert, C. R., Mantini, D., Bulthe, J., Sunaert, S., WOuters, J., & Ghesquiere, P. (2013) Intact but less accessible phonetic representations in adults with dyslexia. Science, 342, 1251-1254. doi:10.1126/science.1244333

Browne, M. W. (1988, Feb 16). Simple tests developed to diagnose dyslxia. New York Times, p.19Y. Retrieved from: .

Finn, E. S., Shen, X., Holahan, J. M., Scheinost, D., Lacadie, C., Papademetris, X., Shaywitz, S. E., Shaywitz, B. A., & Constable, R. T. (2014) Disruption of functional networks in dyslexia: A whole-brain, data-driven analysis of connectivity. Biological Psychiatry, 76, 397-404. .

Kolata, G. (1987, December 8). New clues to complex biology of dyslexia. New York Times, p.23Y.

Norton, E. S., Beach, S. D., & Gabrieli, J. D. E. (2015) Neurobiology of dyslexia. Current Opinion in Neurobiology, 30, 73-78.

Tamboer, P., Vorst, H. C. M., Ghebreab, S., & Scholte, H. S. (2016) Machine learning and dyslexia: Classification of individual structural neuro-imaging scans of students with and without dyslexia. NeuroImage: Clinical, 11, 508-514.

Tierney, A. T. & Kraus, N. (2013) The ability to tap to a beat relates to cognitive, linguistic, and perceptual skills. Brain and Language, 124, 225-231. doi:10.1016/j.bandl.2012.12.014

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