Types of Dyslexia: Definition, Symptoms, and Causes
Dyslexia is the most prevalent learning disorder. It is detected especially during the school stage, and affects the reading processes, which end up impacting on and hindering the writing processes.
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 analyse the characteristics of each one of them and see the differences they present, as well as their symptoms.
Types of Dyslexia
Dyslexia is a learning disorder characterized by difficulty in reading correctly . Such difficulty translates into symptoms such as swapping letters when reading, confusion and/or omission of words during reading. In addition, it can (and often does) lead to writing difficulties.
This is a very prevalent disorder among children and adolescents (especially boys). Specifically, it accounts for 80 per cent of learning disabilities. Its prevalence is estimated at between 2 and 8 per cent of children in school.
However, we find different types of dyslexia . We can classify them according to various parameters. We will focus on two: according to the reading pathway affected and according to the origin. But first, we will see what is meant by reading pathways through the theory of the double pathway.
When we learn to read, we can do so through various reading paths: the direct or visual path and the indirect or phonological path. These two paths are the concepts raised by the theory of the double path of reading.
In order to understand the different types of dyslexia that exist depending on the pathway, we must first understand how each of the possible reading pathways works, because depending on whether one or the other pathway is affected, the type of dyslexia will be one or the other.
1. Visual pathway
The visual pathway is also called the direct pathway or lexical pathway . When we use this pathway, we look at the graphic representation of the words, and relate it to the meaning of the words. As its name indicates, it is a pathway that is centered on sight, and it makes us read the words “globally”, without spelling them out letter by letter.
From this way, we go from the words (through 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 way is also called the indirect or sequential way ; 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, we use a phonemic coding, spelling letter by letter, sound by sound, to form the word. This 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 affected pathway
The first parameter or criterion we will use to classify the different types of dyslexia is according to the affected pathway. 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 the dyslexia corresponds to the affected pathway. This type of dyslexia is also called superficial dyslexia.
A subject who presents it will have difficulty reading irregular words; that is, “atypical” words, with special rules of writing, which deviate from the usual pattern (such as irregular verbs).
This dyslexia is also called visual-perceptual dyslexia, as the visual pathway is affected. What happens in this type of dyslexia is that the person, not being able to read globally, because he has the visual pathway affected, has to read letter by letter, decoding phonema-grapheme.
Other associated symptoms
In addition, lexical dyslexia usually appears at age 7 or 8 (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 problems in reading comprehension and has an altered writing (writes with inversions).
Finally, another characteristic symptom is the alteration in perceptual-visual skills when solving visual problems or locating objects.
2. Phonological dyslexia
The second of the types of dyslexia according to the affected pathway is phonological dyslexia, in which the phonological pathway (non-lexical, indirect or sequential) is affected. The main difficulties here are reading pseudo-words (i.e., words that do not exist, invented).
This can be explained in the following way: the person who suffers from it, not being able to read letter by letter accessing the meaning of the words, because he has the affected phonological pathway, must use the visual or direct pathway. And, since they cannot decode phonema-grapheme, they will have difficulty reading words that do not really exist, since they will have to read them globally, and since they do not exist (and are not used to them), the difficulty of processing them will appear.
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 old. The accompanying disorders are related to immediate auditory memory. In addition, 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. Deep dyslexia
The last of the types of dyslexia is deep dyslexia, the most severe . It is also called mixed dyslexia, as both the visual and phonological pathways are affected. Specifically, however, the most affected is the phonological pathway (which cannot be used at all); in contrast, the visual pathway is partially preserved, and that is why the subject is the only one who can use it (in part).
In this case, the subject has difficulty reading all the words, whether regular, irregular or pseudo-words. That is why reading comprehension in this case is null.
According to origin
The second criterion we will use to classify the different types of dyslexia is according to their 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 linked to genetic disorders and a delay in maturation. It affects from birth; however, it can obviously be detected when the child starts learning to read. It is more common than the next type of dyslexia (acquired dyslexia).
2. Acquired dyslexia
In this case, the acquired dyslexia has its origin in a brain injury affecting one or more areas of the brain involved in the processes of reading and writing. Depending on the age of the child at the time of the injury, his or her brain plasticity, the cognitive stimulation he or she receives afterwards, and other variables, the dyslexia that will appear will be more or less severe, and more or less temporary.
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Andalusian Dyslexia Association (Asandis). (2010). General Guide to Dyslexia.
Tamayo, S. (2017). Dyslexia and difficulties in the acquisition of literacy. Profesorado, revista de currículum y formación del profesorado, 21(1): 423-432.