Defining Dyslexia
The morphemes in the word “dyslexia” combine the Greek roots “difficulty” (dys) with “words” (lex). Therefore, the basic definition of dyslexia is a primary difficulty at the word level, as opposed to difficulty at the sentence or paragraph level. In 2002, the IDA (International Dyslexia Association) approved a comprehensive and widely used definition of dyslexia that was written by a team of dyslexia experts and researchers. The definition states:
“Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/ or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede the growth of vocabulary and background knowledge.”
Let’s break this definition down piece by piece.
Specific Learning Disability:
Specific learning disability (SLD) is a category taken from the federal legislation–Individuals with Disabilities Education Act (IDEA, 2004)–that guides decisions regarding who qualifies for special education services.
There are 13 disability categories under IDEA of which SLD is the most common. SLD is defined in Title 20 United States Code Section 1401(30) as:
“… a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, that may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or to do mathematical calculations, including conditions such as perceptual disabilities, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia … does not include learning problems that are primarily the result of visual, hearing, or motor disabilities, of intellectual disability, of emotional disturbance, or of environmental, cultural, or economic disadvantage” (IDEA, 2004).
What does it mean that dyslexia is neurobiological in origin?
It is important to understand that dyslexia originates within the brain. Functional brain imaging has allowed researchers to understand the disruption in neural systems among individuals with dyslexia. In other words, individuals with dyslexia have brains that are often wired differently; there are specific areas in our brains that communicate with each other to make reading possible, and for individuals with dyslexia, these areas do not communicate with each other efficiently (Lyon et al., 2003, p.4).
What does it mean that dyslexia is rooted in the phonological component of language?
Even before an individual may learn to read, miscommunications within the brain may disrupt the phonological component of language, or an individual’s ability to perceive, manipulate, and recall the sounds of language. As a result, the individual may have difficulty understanding that sounds correspond to letters and that letters make up words (Moats, 2008). Additionally, the individual may have difficulty with the storage, retrieval, and articulation of words. In other words, students with dyslexia may attribute their difficulty with reading to origins based in the phonological component of reading.
What about the claim that dyslexia is “unexpected”?
Dyslexia has historically been conceptualized as “reading (and spelling) difficulties that are ‘out of line’ with expectation, given age and IQ” (Snowling et al., 2020, p. 502). This idea–that the reading challenges are “unexpected”–is also known as a “discrepancy” model, meaning that a diagnosis of dyslexia required identification of a difference between a student’s reading performance and their intelligence based on cognitive testing (Tanaka & Hoeft, 2017; IDA Dyslexia Handbook, 2019). While a discrepancy may occur for some individuals with dyslexia, evidence of a discrepancy is no longer a requirement for diagnosis. The Diagnostic and Statistical Manual of Mental Disorders (DSM) removed this criteria in its 5th edition revisions (Tannock, n.d.), and the Individuals with Disabilities Education Act (IDEA, 2024) does not use this as a criteria when determining eligibility for special education services (Tanaka & Hoeft, 2017).
In a presentation at The Dyslexia Foundation Conference (2024), Dr. Phil Capin, an assistant professor at Harvard Graduate School of Education, describes problematic characteristics of using the term “unexpected” in the definition of dyslexia, including:
- Reading development can impact student performance on intelligence measures and vice versa.
- IQ does not give meaningful information about student reading performance in the future.
- Whether or not this criteria is used “may allow individuals to decide which students with word reading difficulties are deserving and undeserving of treatment.” Lyon, Shaywitz, and Shaywitz add an additional caution, suggesting that simply looking for a discrepancy between reading ability and IQ can result in a delay of important services and essential reading instruction, and therefore the discrepancy between these two factors should not necessarily be a requirement for diagnosis (Lyon et al., 2003, p. 8).
It is also important to note the role of instruction. Historically, dyslexia could not be attributed to poor instruction or a lack of instruction (Lyon et al., 2003, p. 8). Shaywitz, Shaywitz, and Lyons believe that this is still true, but urge professionals and parents to closely examine the type of reading instruction. They note, “Specifically the lack of response to scientifically informed instruction is one factor that differentiates severe and intractable reading deficits from reading failure resulting from inadequate instruction” (Lyon et al., 2003, p. 9).
What are the secondary consequences associated with dyslexia?
Finally, in the definition of dyslexia, the term “secondary consequences” refers to the other issues that come hand in hand when a person with dyslexia has difficulty processing language, such as reading comprehension, vocabulary acquisition, written expression, spelling, and other academic tasks required for success in school (Moats, 2008). In other words, dyslexia is often comorbid with other learning challenges and does not often occur in isolation.
References:
Capin, P. & Miciak, J. (2024, November 8). Recognizing dyslexia: Universal screening and assessment, early intervening services and special education services [Conference presentation]. The Dyslexia Foundation (TDF) Conference, Boston, MA.
Individuals With Disabilities Education Act, 20 U.S.C. § 1400 (2004).
International Dyslexia Association. (2002). Definition of dyslexia. https://dyslexiaida.org/definition-of-dyslexia/
International Dyslexia Association. (2019). IDA Dyslexia handbook: What every family should know. https://www.readingrockets.org/sites/default/files/guide/IDA-Dyslexia-Handbook-2019.pdf
Landi, N., & Ryherd, K. (2017). Understanding specific reading comprehension deficit: A review. Language and Linguistics Compass, 11(2). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6051548/
Lyon, G. R., Shaywitz, S. E., & Shaywitz, B. A. (2003). A definition of dyslexia. Annals of Dyslexia, 53, 1–14. https://doi.org/10.1007/s11881-003-0001-9
Moats, L. C., & Dakin, K. E. (2008). Basic facts about dyslexia and other reading problems. International Dyslexia Association.
Snowling, M.J., Hulme, C., Nation, K. (2020). Defining and understanding dyslexia: Past, present and future. Oxford Review of Education, 46(4), 501-513.
Tanaka, H., & Hoeft, F. (2017). Time to revisit reading discrepancies in twice exceptional students? International Dyslexia Association. https://dyslexiaida.org/time-to-revisit-reading-discrepancies-in-twice-exceptional-students/
Tannock, R. (n.d.). DSM-5 changes in diagnostic criteria for Specific Learning Disabilities (SLD): What are the implications? International Dyslexia Association. https://dyslexiaida.org/dsm-5-changes-in-diagnostic-criteria-for-specific-learning-disabilities-sld1-what-are-the-implications/
