Dyslexia is understood as a difficulty in reading and is a very common disorder in the population.. Let’s see what forms it can manifest itself in depending on whether it is acquired or developmental.
Acquired alexias or dyslexias will be classified according to whether or not they present reading impairment combined with alterations in writing or oral expression. With respect to developmental or non-acquired dyslexia, it will show different classifications depending on whether the neuropsychological model or the cognitive model is used.
It is important and useful to know what type of alteration each subject presents in order to be able to better adapt the type of treatment to his or her specific difficulty and thus intervene more effectively. the specific difficulty and thus intervene more effectively. In this article we will mention what is meant by dyslexia, as well as the different types according to the cause of the disorder (acquired or not) and according to the different perspectives of study.
What is dyslexia?
Dyslexia, also called specific reading delay, is a specific inability to recognize and decode words.Dyslexia, as mentioned above, is related to reading without difficulty in understanding oral explanations. In individuals with this type of impairment we observe difficulties in reading skills as opposed to intellectual capacity and performance in other areas that are not impaired.
The Developmental Dyslexia Research Group highlights other characteristics of this term, referring to a difficulty in learning to read despite adequate conventional instructions and good intelligence. The disorder is linked to basic cognitive deficits.
Regarding the diagnostic criteria, the Diagnostic Manual of the American Psychological Association classifies dyslexia within the group of specific learning disorders.The general criteria (A) are difficulties in learning and use of academic skills, for more than 6 months, in spite of specific interventions.
With regard to the tenth edition of the International Classification of Diseases Manual, it notes that one of the following must be met: reading performance at least 2 standard deviations below that expected for age and IQ or a history of reading difficulty and spelling scores at least 2 standard deviations below that expected. Similarly, these difficulties must cause interference.
What kinds of dyslexia are there?
Dyslexia was classified into two main groups according to whether it is acquired or alexia, i.e. the individual was not born with these alterations, there was a trauma or damage to the brain that caused the difficulty in reading or whether it is developmental or not acquired, in this case there is no external alteration. There was already a predisposition in the subject. Within the latter we will see that they are divided according to the neuropsychological model and the cognitive model.
As we have already pointed out, in these individuals there are alterations in reading caused by acquired damage, not present in the individual from birth.
1.1. Pure alexia
Pure alexia is associated with great difficulty in decoding words, syllables or letters.. It consists of relating letters and sounds and giving them meaning. This type of alexia is also known as “pure word blindness”, this alteration is due to a lesion in the left visual cortex and in the posterior part of the corpus callosum, a structure that connects the right cerebral hemisphere with the left hemisphere. These subjects present problems in reading and can write perfectly.
The authors Hecaen and Kremin will make a division of the pure alexias classifying them in verbal alexias, they maintain the capacity to recognize letters individually, they can spell them, but they are unable to read words. In this type of pure alexia the lesion is located in the occipital lobe or literal alexia, they can read words perfectly but it is impossible to read separate letters or spell them. In this case the lesion occurs in the parieto-occipital area.
1.2. Alexia with agraphia
In alexia with agraphia, as the name indicates, there is an alteration in both reading (alexia) and writing (agraphia).This is in addition to anomia, difficulty in naming an object or concept, and apraxia, complications in performing tasks or movements. In this type of alexia there is a global alteration of written language, both for reading and writing. Lesions will be observed in the superior area of the parietal lobe and in the pathways (entrance) to the temporal and occipital lobes.
Alexia with aphasia
In alexia with aphasia there will be a difficulty in reading associated with an altered associated with an alteration in the expression of oral language.In alexia with aphasia, aphasia is linked to an impairment in communication.
2. Developmental dyslexia
Developmental or non-acquired dyslexia has been classified in different ways according to different authors.. Despite the differences in the way of classification, both neuropsychological and cognitive models, already mentioned above, value the distinction between the different types of developmental dyslexia and therefore the need to make a division in order to better adapt the intervention to each specific alteration presented by the subject.
This model attempts to classify the different subtypes of dyslexia at first according to clinical data, and then using the technique of multivariate analysis. Depending on the methodological techniques used, a different number of subtypes will appear.
2.1.1. Perceptual-visual dyslexia
As the name indicates, in this subtype the disturbances are more the disturbances will be more related to visual perceptual impairment.. There is an alteration in simultaneous processing, in the perception of different stimuli at the same time, this affectation will result in problems in visual perceptual and motor skills and in immediate visual memory, which is stored in our brain for approximately 1 minute.
Perceptual-visual dyslexia occurs in a higher percentage in children between 7 and 8 years old, in younger subjects. It is usually observed earlier since it has been shown that when individuals begin to read, they first use perceptual processes.
These neurological alterations mentioned above are translated into problems in reading and spelling: slow word recognition is observedDyslexia: slow word recognition is observed; confusion of letters and words of similar spelling, i.e., they are written in pairs; reading comprehension is variable; writing may be presented in mirror, as if reflected in a mirror, first the last letter of the word and at the end the first; confusion and inversion of letters, words or numbers of similar spelling is also produced.
2.1.2. Auditory-linguistic dyslexia
Given the impairment linked to auditory processes, the impairment will be observed more at the level of sequential processing.This type of developmental dyslexia is more common in older children between the ages of 9 and 12, who require greater mastery of reading and already introduce linguistic aspects.
This type of developmental dyslexia occurs more in older children, between 9 and 12 years of age, who require greater mastery of reading and linguistic aspects are already introduced.
The affectations in this subtype of reading impairment will be related to: confusion of letters and words that sound similar; difficulties in reading comprehension, omitting, adding and substituting letters in words with similar sounds; syntactic errors, in the hierarchy of words when they are grouped together, and difficulty in writing.
2.1.3. Mixed dyslexia
As the name indicates, in this type of developmental dyslexia both visual and auditory processing difficulties are observed. The main features are a variable ability to decode (translate letters into sounds) and no reading comprehension. There are also orthographic alterations with general affectation in dictation and difficulty in writing words with paired meanings.
2.2. Cognitive perspective
This model conceives dyslexia as a deficit in phonological processing abilities, conscious operations to name, segment, memorize and group sounds related to linguistic units. This model has mainly used individual case studies to classify the different subtypes.
This perspective uses the dual pathway theory to explain the different impairments.. The theory describes two independent but complementary pathways that enable reading comprehension.
First, the lexical, direct or superficial pathway links the meaning of words with their graphic representation, thus, for this pathway a correct simultaneous processing and good visual perceptual abilities are necessary. On the other hand, the phonological, indirect or non-lexical pathway relates the meaning of words with their sound, requiring a good sequential processing so that a correct decoding of the word can be performed, using the processes of grapheme-phoneme conversion, i.e., letter-sound.
2.2.1. Superficial Dyslexia
In this subtype of developmental dyslexia, the main alteration is the difficulty in reading difficulty in reading irregular words that are spelled differently from how they are pronounced.. The affectation occurs in the lexical pathway, therefore the phonological pathway will be used, making use of grapheme-phoneme conversion. Subjects with this alteration can read regular words or pseudowords (words without meaning) without any problem.
The main errors observed are the omission, addition or substitution of letters, they read nouns better than adjectives, and verbs are the worst thing they read.
2.2.2. Phonological Dyslexia
As the main alteration, phonological dyslexia presents difficulty in reading pseudo-words, generated by an alteration in the reading of nouns.generated by alterations in the phonological pathway. Thus, the lexical pathway will be used, being able to read regular and irregular words. As they use the meaning-relation pathway, if the word is not known or familiar, they will not be able to make sense of it. They tend to read pseudowords as real words and confuse visually similar words.
2.2.3. Deep dyslexia
There will be severe impairment in the non-lexical pathway and variable impairment in the lexical pathway, with only the lexical pathway being used and problems being observed in all word classes. Subjects with this impairment achieve better comprehension of words when they read them to themselves than when they are read aloud. and it also helps them to find words in context rather than in isolation.
The most representative errors are semantic, related to meaning, for example, “pear” would be changed to “apple”; visual or derivational paralexies, confusing similar letters and creation of neologisms, new words.