So, what exactly is Dyslexia?
Well, let's start with the most widely accepted definition created in 2002 by the National Institute Of Child Health and Development:
"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 growth of vocabulary and background knowledge."
So, now that we have the formalities out of the way - let's unpack that!
Dyslexia is an unexpected difficulty in reading. What I mean by unexpected is that Dyslexia is unexpected in relation to the student's cognitive ability, motivation, and exposure to reasonably effective reading instruction.
It is highly hereditary in nature. Research actually shows us that there is a 50% chance of diagnosis when a parent or sibling has it.
The core weakness in Dyslexia is related to students' accurate and efficient pairing between the sounds in words (phonological processing) and their corresponding letter or letter patterns. This often results in lagging skills in sight word recognition, decoding, overall reading fluency, and can also impact spelling. And then as a result of word reading difficulties, students with dyslexia are exposed to a significantly smaller volume of expository and narrative texts, thereby limiting their development of vocabulary and background knowledge. This is referred to as the Matthew Effect. Students with Dyslexia can also have lagging skills in spoken language and struggle to express themselves clearly or comprehend what others mean when they speak.
So now that you know what Dyslexia is, did you know that there are subtypes of Dyslexia?
Distinct groups or subtypes of Dyslexic readers have emerged in a series of research studies conducted over the last twenty years. So researchers have attempted to group commonly observed behaviors into different categories.
The most common subtypes include a Phonological Deficit and a Naming Speed Deficit.
The phonological subtype impacts phonological awareness and decoding, sight word and passage accuracy. This subtype is characterized as below average performance on standardized measures of phonemic awareness and assessments of decoding, sight word and/or passage accuracy. These weaknesses impact accuracy of reading single words and connected text.
The Naming Speed Subtype impacts Rapid Automatized Naming, Decoding Efficiency, Sight Word Efficiency, and Passage Fluency. Naming speed deficits are characterized by below average performance on standardized measures of rapid automatized naming, particularly subtests involving letter naming, and measures of decoding word reading efficiency (i.e. timed measures of sight word recognition and decoding). These weaknesses impact fluency in reading sentences and passages.
The combination of both deficits in some students results in a reading impairment that is more severe than in students with a single deficit. The Double Deficit Subtype includes impairments in both phonological and naming speed subtypes. Students with a double deficit demonstrate below average performance in both areas. These weaknesses impact accuracy of reading single words and connected text and fluency in reading sentences and passages.
Regardless of the subtype, Dyslexia is a neurological disability, but the exact cause is still unclear. Despite this, brain imaging shows differences in the way a Dyslexic brain develops and functions. Specifically, Dyslexic brains have been found to have difficulties in identifying separate speech sounds within a word and/or learning how letters represent those sounds
Dyslexia is not the result of the daily struggle of learning to read, but rather the result of a unique neurological profile. And as a result, the impact of Dyslexia is different for each person.
We used to think it was more visual in nature, meaning that the disability could be seen in things like letter reversals, seeing or reading words backwards, or letter confusions, but...
Research now shows us that it is not a visual disability, but rather, it is a language-based disability. The "visual" issues that we observe are actually indicative of difficulties with recalling letter symbols for sounds and letter patterns in words.
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Brady, Susan. 2019. âThe 2003 IDA definition of dyslexia: A call for changes.â Perspectives on Language and Literacy 45, no. 1: 15-21.
Keys to Literacy, Understanding Dyslexia, course
Kilpatrick, David A. "Essentials of assessing, preventing, and overcoming reading difficulties." Hoboken, New Jersey : Wiley, 2015.
Shaywitz, Sally E., and Bennett A. Shaywitz. 2020. Overcoming Dyslexia: Second Edition, Completely Revised and Updated. New York: Knopf Doubleday Publishing Group.