So What EXACTLY Is Dyslexia? (Part I)

Originally published here on June 3, 2008.

That is the ten thousand dollar question...

I recently participated in a discussion on the International Reading Association's listserv for teachers, a discussion in which the exact definition of dyslexia featured prominently. As a backdrop to that discussion, let me show you what I found when I went looking for a definition online.

• Speakability, a UK-based support group for people with aphasia, defines dyslexia simply as "difficulty reading."


• The Communications Forum, another UK-based support group for people with communications disorders, dresses their definition up with a few details: "Difficulty with written language. Dyslexia affects reading, spelling, writing, memory and concentration. Sometimes called a specific learning difficulty. Dyslexia can be developmental or acquired."


• Shannon Booth, a neuroscience major at a college in Minnesota, has a definition online that seems simplistic to me, but reflects common perceptions: "A disorder where things are done or read backwards. For example, a "d" and a "b" might be confused."


• inURarea, a UK-based childcare group, expands the definition slightly to exclude some reading problems based on "sensory defect" and specify that it is a neurological condition: "Difficulty in reading due to a defect of brain function other than sensory defect."


• The Nebraska Department of Education says dyslexia is "a developmental reading disability, presumably congenital and perhaps hereditary, that may vary in degree from mild to severe."


• Child Care Aware defines dyslexia as "an impairment in the brain's processing of information that results in difficulty reading, spelling, writing, and related language skills."


• One high school science teacher says that dyslexia is an "impairment in the visual cortex that leads to difficulty in learning to read, write, or spell."

You can probably guess from those seven examples that definitions of dyslexia are spread out along a continuum ranging from the simple two word "reading difficulty" to formulas that are tediously long and complicated. They also range from vague generalities (half the people I know have difficulty reading) to somewhat more specific ideas (like being congenital and hereditary) and the nature and location of the disorder.

The term "dyslexia" was coined by an eye doctor in Stuttgart, Germany, in 1881. While the scientific community has been tinkering with the condition for over 125 years, most of the definitions during the first hundred years are best described as "exclusionary." That is to say that a doctor or therapist would exclude causes for poor reading (is it poor eyesight?...no; is it low IQ?...no; is it a hearing problem?... no; is it lack of access to education?...no), and when the doctor ran out of other choices, the reading problem was determined to be dyslexia. Theories existed about what caused dyslexia, or how dyslexia worked to cause the problems seen in a patient; but the technology to test those theories, to observe brain function, didn't exist until recently.

The growth of linguistics led to new ideas about dyslexia in the 1970's - ideas that revolved about brain function and the processing of the sounds in a language. Phonemic awareness has become one focus of research into dyslexia. If children had some problem identifying the psychological sound units of their language, associating those sounds with symbols (letters) would obviously present problems - and reading would be affected.

The development of neuroimaging in the 1980's and 90's has further served to promote research into dyslexia. It is now possible to observe some aspect of brain function in a living person without invasive techniques like surgery. And far more data on brain function can be obtained than was possible in the past.