Types of dyslexia: definition, symptoms and causes
dyslexia It is the most prevalent disorder in terms of learning disorders. It is especially detected during the school stage, and affects reading processes, which end up having an impact and making writing processes difficult.
In this article we will know the three types of dyslexia according to the affected reading pathway, and the two types of dyslexia according to their origin. We will analyze the characteristics of each one of them and we will see the differences that they present, as well as their symptoms.
types of dyslexia
Dyslexia is a learning disorder characterized by the difficulty of reading correctly.. This difficulty translates into symptoms such as interchanging letters when reading, confusing them and/or omitting words while reading. In addition, it can also (and often does) lead to writing difficulties.
It is a highly prevalent disorder among children and adolescents (especially boys). Specifically, it constitutes 80% of the cases of learning disorders. It is estimated that its prevalence is between 2 and 8% of school children.
However, we find different types of dyslexia. We can classify them according to various parameters. We will focus on two: according to the affected reading path and according to the origin. But first, let's see what is meant by reading paths through the double path theory.
two-way theory
When we learn to read, we can do it through different ways of reading: the direct or visual way and the indirect or phonological way. These two ways are the concepts that the theory of the double way of reading raises.
To understand the different types of dyslexia that exist according to the pathway affected, we must first understand how they work. each of the possible ways of reading, since depending on whether one way or another is affected, the type of dyslexia will be one or other.
1. visual pathway
The visual route is also called the direct route or the lexical route.. When we use this way, we look at the graphic representation of the words, and we relate it to their meaning. As its name suggests, it is a sight-focused pathway, and it makes us read words “globally”, without spelling them out letter by letter.
From this path, we go from words (by means of a gestalt and global perception of them) to the meaning of the term, and later to its pronunciation (we read).
2. phonological pathway
This second path is also called an indirect or sequential path.; when we use it in reading, we focus on the sounds of the letters to transform them into words, through a process of grapheme-phoneme conversion.
That is to say, we are based on using a phonemic coding, spelling letter by letter, sound by sound, you have to form the word. That is why it is also called sequential or indirect.
Unlike the visual pathway, the mechanism of the phonological pathway involves accessing the word, decoding it phoneme to grapheme, pronouncing it, and finally accessing its meaning.
Depending on the pathway affected
The first parameter or criterion that we will use to classify the different types of dyslexia is according to the pathway affected. Thus, as we already announced, depending on whether the lexical pathway, the phonological pathway or both are affected, we find three types of dyslexia:
1. lexical dyslexia
The first of the types of dyslexia is lexical dyslexia, where the affected pathway is the lexical pathway.. We should always think that the name of dyslexia corresponds to the affected pathway. This type of dyslexia is also called surface dyslexia.
A subject that presents it will have difficulties in reading irregular words; that is to say, “atypical” words, with special writing rules, that deviate from the usual pattern (such as irregular verbs).
This dyslexia is also called perceptual-visual dyslexia, since the visual pathway is affected. What happens in this type of dyslexia is that the person, unable to read globally, because they have an affected visual pathway, has to read letter by letter, decoding phoneme-grapheme.
Other associated symptoms
In addition, lexical dyslexia usually appears at 7 or 8 years of age (unlike others that appear later). It is also accompanied by deficits in psychomotor skills and immediate memory (which allows us to remember events that have just occurred). The person confuses the letters when reading, shows reading comprehension problems and has altered writing (writes with inversions).
Finally, another characteristic symptom is the alteration in perceptual-visual skills when it comes to solving visual problems or locating objects.
2. Phonological dyslexia
The second type of dyslexia according to the pathway affected is phonological dyslexia, in which the phonological pathway (non-lexical, indirect or sequential) is affected. The main difficulties are, in this case, reading pseudowords (ie words that do not exist, made up).
This is explained as follows: the person who suffers from it, not being able to read letter by letter by accessing to the meaning of the words, because she has the phonological pathway affected, she should use the visual or direct pathway. And, not being able to decode phoneme-grapheme, she will have difficulties reading words that do not really exist, since she should read them globally, and since they don't exist (and she's not used to them), there will appear the difficulty of process them.
Other associated symptoms
This type of dyslexia is also called auditory-linguistic dyslexia. It usually appears later than the previous one, in children between 9 and 12 years of age. The alterations that accompany it are related to immediate auditory memory. Also, the person confuses words that have a similar sound and skips letters when reading (omits them).
On the other hand, as in visual dyslexia, the subject presents changes in writing, making syntactic errors, as well as poor reading comprehension.
3. profound dyslexia
The last of the types of dyslexia is profound dyslexia, the most serious. It is also called mixed dyslexia, since both pathways are affected; the visual and the phonological. Specifically, but the most affected is the phonological pathway (which cannot be used at all); instead, the visual pathway is partially preserved, and that is why the subject is the only one that can be used (in part).
In this case, the subject has difficulty reading all words, whether regular, irregular, or pseudowords. That is why reading comprehension in this case is zero.
According to the origin
The second criterion that we will use to classify the different types of dyslexia is according to its origin.. Thus, we find two types of dyslexia, we know them below.
1. developmental dyslexia
This dyslexia is also called developmental dyslexia.. Its origin is unknown, but it has been related to genetic alterations and a delay in maturation. Affects from birth; however, obviously you can begin to detect when the boy or girl begins to learn to read. It is more common than the next type of dyslexia (acquired dyslexia).
2. acquired dyslexia
In this case, acquired dyslexia has its origin in a brain lesion that affects one or more areas of the brain involved in literacy processes. Depending on the age of the child at the time of the injury, his brain plasticityDepending on the cognitive stimulation that he receives later and other variables, the dyslexia that will appear will be more or less severe, and more or less temporary.
Bibliographic references:
American Psychiatric Association –APA- (2014). DSM-5. Diagnostic and Statistical Manual of Mental Disorders. Madrid: Pan American.
Andalusian Dyslexia Association (Asandis). (2010). General Guide on Dyslexia.
Tamayo, S. (2017). Dyslexia and difficulties in the acquisition of reading and writing. Faculty, Curriculum and Teacher Training Magazine, 21(1): 423-432.
