Types of dyslexia - definition, symptoms and causes

There are different subtypes of this learning disorder. These are described below.

Dyslexia is the most prevalent learning disorder. It is detected especially during the school stage, and affects the reading processes, which end up having repercussions and hindering the writing processes.

In this article we will learn about the three types of dyslexia according to the reading pathway affected.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 they present, as well as their symptoms.

Types of dyslexia

Dyslexia is a learning disorder characterized by the difficulty in reading correctly.. This difficulty translates into symptoms such as interchanging letters while reading, confusing letters and/or omitting words while reading. In addition, it can (and often does) lead to writing difficulties.

It is a very prevalent disorder among children and adolescents (especially boys). Specifically, it accounts for 80% of all cases of learning disorders. Its prevalence is estimated to be between 2 and 8% of school children.

However, there are different types of dyslexia, there are 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, let's see what is meant by reading pathways through the dual pathway theory.

Dual pathway theory

When we learn to read, we can do so through different reading pathways: the direct or visual pathway and the indirect or phonological pathway. These two pathways are the concepts proposed by the two-way theory of reading.

To understand the different types of dyslexia that exist according to the affected pathway, we must first understand how each of the possible ways of reading work, because depending on whether one or another pathway is affected, the type of dyslexia will be one or another.

1. Visual pathway

The visual pathway is also called the direct pathway or the lexical pathway.. When we use this pathway, we look at the graphic representation of words and relate it to their meaning. As its name indicates, it is a pathway centered on sight, and causes us to read words "globally", without spelling letter by letter.

From this pathway, we go from the words (through a gestalt and global perception of them) to the meaning of the term, and then to its pronunciation (we read).

Phonological pathway

This second pathway is also called the indirect or sequential pathway.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 rely on using a phonemic encoding, 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 by grapheme, pronouncing it and finally accessing its meaning.

According to 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 have already announced, depending on whether the lexical pathway is affected, the phonological pathway or both, we find three types of dyslexia:

1. Lexical dyslexia

The first type 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 with this type of dyslexia will have difficulty reading irregular words, i.e. "atypical" words, with special writing rules, which deviate from the usual pattern (such as irregular verbs).

This dyslexia is also called perceptual-visual dyslexia, as the visual pathway is affected. What happens in this type of dyslexia is that the person, unable to read globally, because the visual pathway is affected, 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 (that which allows us to remember events that have just occurred). The person confuses letters when reading, shows reading comprehension problems and has an altered handwriting (writing with inversions).

Finally, another characteristic symptom is the alteration in visual-perceptual skills when solving visual problems or locating objects.

2. Phonological dyslexia

The second type of dyslexia according to the affected pathway is phonological dyslexia, in which the phonological pathway (non-lexical, non-lexical, indirect) is affected. (non-lexical, indirect or sequential) is affected. The main difficulties are, in this case, reading pseudowords (i.e., words that do not exist, invented).

This is explained as follows: the sufferer, unable to read letter by letter to access the meaning of the words, because the phonological pathway is affected, must use the visual or direct pathway. And, not being able to decode phoneme-grapheme, she will have difficulties in reading words that do not really exist, since she will have to read them globally, and as they do not exist (and she is not used to them), the difficulty in 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 of age. The accompanying disturbances 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 type.. It is also called mixed dyslexia, since both visual and phonological pathways are affected. Specifically, however, the most affected is the phonological pathway (which cannot be used at all); on the other hand, the visual pathway is partially preserved, and that is why the subject is the only one he/she can use (in part).

In this case, the subject has difficulty reading all words, whether they are regular, irregular or pseudowords. This 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, there are two types of dyslexia, which are described below.

Developmental dyslexia

This dyslexia is also called developmental dyslexia.. Its origin is unknown, but it has been related to genetic alterations and maturational delay. It affects from birth; however, it can obviously begin to 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 acquired dyslexia has its origin in a brain lesion that affects one or more areas of the brain involved in reading processes. involved in the processes of reading and writing. Depending on the child's age at the time of the lesion, his or her brain plasticity, the cognitive stimulation he or she subsequently receives and other variables, the dyslexia that will appear will be more or less severe, and more or less temporary.

Bibliographical references:

• American Psychiatric Association -APA- (2014). DSM-5. Diagnostic and statistical manual of mental disorders. Madrid: Panamericana.

• Andalusian Dyslexia Association (Asandis). (2010). General guide on Dyslexia.

• Tamayo, S. (2017). Dyslexia and difficulties in literacy acquisition. Profesorado, revista de currículum y formación del profesorado, 21(1): 423-432.