The dyslexia is a specific learning difficulty neurobiological origin that occurs in children and adults. It is characterized by a difficulty in the accuracy / fluency of word recognition and by deficiencies in spelling and decoding skills.
In addition, it can cause other secondary consequences such as problems of comprehension or reduction of the reading experience that can stop the acquisition of vocabulary and the acquisition of other basic knowledge (International Dyslexia Association, 2016).
The terms disorder of learning to read and dyslexia are synonymous. In general, all children learn to read without specific difficulties; but, approximately 25% may experience some type of acquisition problem at some point in their school years. However, only a very small group is diagnosed with dyslexia (Matute, Ardila and Roselli, 2010).
Dyslexia in Children
The main characteristics of dyslexia is the difficulty to learn to read, in spite of this, not all children who have problems to develop this learning are diagnosed with dyslexia (Matute, Ardila and Roselli, 2010).
Although it affects an important part of the child population and is considered one of the most alarming causes of school failure, there is no general agreement about its etiology, cognitive mechanisms involved, and even about its categorical characterization (Artigas-Pallarés , 2009).
Current scientific trends suggest that this disorder has an evident neurobiological and genetic basis and that at a cognitive level, it is a consequence of a failure in the phonological processing that we perform of the information (López-Escribano, 2007).
What is dyslexia?
Already at the end of the 19th century, the first observations of people of infantile age who had difficulties in learning to read were made (Matute, Ardila and Roselli, 2010).
It is in this period when the first descriptions of patients who after a brain injury acquire a reading disorder, which was called alexia (Matute, Ardila and Roselli, 2010) are also made.
On the other hand, the investigations of Orton during the first decades of the last century, highlighted the tendency to rotations and inversion of symbols, observed in many children with reading learning problems. In addition, he pointed out the prevalence of left-handedness in these children or the existence of a mixed laterality (Matute, Ardila and Roselli, 2010).
In the final decades of the 20th century, the first definition of dyslexia appears that grants a clinical status, from which three essential points have been derived: Matute, Ardila and Roselli, 2010):
- The sociocultural and school context are not responsible for the specific reading disorder.
- There are difficulties in the cognitive sphere that affect the learning of reading.
- The disorder has a biological origin.
In these ways, all these characteristics have been specified in the current definition of dyslexia:
“Dyslexia is a specific learning disorder whose origin is neurobiological. It is
characterized by difficulties in accuracy and / or fluency in word recognition and poor spelling and decoding skills. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive skills and received school instruction. Secondary consequences include problems in reading comprehension and a reduced reading experience that limit the growth of vocabulary and information management ” (International Dyslexia Association, 2016).
Dyslexia affects those who suffer from it throughout their lives; however, the impact can be modified in the different stages. It can hinder the achievement of academic success and in serious ways, may require special educational adaptations or additional support services (International Dyslexia Association, 2016).
Therefore, dyslexia is a type of disorder that specifically affects a person’s reading ability. These individuals usually present a reading level lower than expected for their age level and general intellectual performance (National Institute of Neurological Disorders and Stroke, 2015).
Although it is a heterogeneous disorder, the common characteristics in all people suffering from dyslexia are (National Institute of Neurological Disorders and Stroke, 2015):
- Difficulties in phonological processing (manipulation of sounds).
- I spell.
- Rapid verbal / visual response
How many people suffer from dyslexia?
The reading learning disorder represents approximately 80% of the cases of people with learning disorders. Different studies have indicated that it is the learning disorder that has the highest prevalence (Matute, Ardila and Roselli, 2010).
The international dyslexia association indicates that in the United States of America approximately 13-14% of the population of school age has some condition susceptible to special education. Of these, around half, are characterized by learning disorders and also, 85% have difficulties in learning to read and language (International Dyslexia Association, 2016).
Despite this, it is estimated that around 15-20% of the population as a whole, have some symptoms of dyslexia, of which not all will be diagnosed with this condition (International Dyslexia Association, 2016).
At a general level, it is accepted that dyslexia has a prevalence of between 5 to 17.5% and that it can be observed in different countries. In spite of this, the specific characteristics of a language and its orthographic system can have different effects on the presence of this disorder (Matute, Ardila and Roselli, 2010).
In the case of the Spanish-speaking population, it is considered that the prevalence of dyslexia may be less because the linguistic system is fairly simple and regular (Matute, Ardila and Roselli, 2010).
On the other hand, it has been observed that dyslexia occurs more frequently in boys than in girls, with a ratio of 1.5 to 1 (Matute, Ardila and Roselli, 2010).
Regarding age, there are notable variations in the different theoretical positions. On the one hand, the hypothesis of delay considers the delay in reading performance disappears with increasing age and school level, while the deficit hypothesis considers that this reading deficit will be maintained throughout life (Matute, Ardila and Roselli, 2010).
Dyslexia can occur in people of all origins and even intellectual levels (International Dyslexia Association, 2016). Despite this, the prevalence may also be affected by child contact with written texts, the development of metalinguistic awareness, the recognition of letters or the ability of phonological segmentation (Matute, Ardila and Roselli, 2010).
Causes of dyslexia
Studies in the area of learning disorders show that dyslexia seems to have a complex genetic and environmental basis. In general, genetic factors can be responsible for between 30-70% of the variability of reading ability (Benitez-Burraco, 2007).
The family history of the disorder is considered the most important risk factor. Specifically, one study has shown that between 35-40% of first-degree relatives of children with dyslexia are also affected by this disorder. In addition, almost 30% of families in which one of its members has been diagnosed have at least one other affected member (Matute, Ardila and Roselli, 2010).
On the other hand, regarding the percentage of variability that does not correspond to the genetic level, some exogenous factors of origin have been identified, among which are: the presence of complications during pregnancy or delivery; the suffering of some type of infection during the embryonic stage; hormonal alterations, epilepsy, among others (Matute, Ardila and Roselli, 2010).
In addition, different structural and functional neuroimaging studies have shown differences in both the way of functioning and brain development of people with dyslexia (International Dyslexia Association, 2016).
Through different positron emission tomography (PET) scans and functional magnetic resonance imaging (MRI), it has shown microscopic cortical abnormalities that reduce connectivity between different areas of the cerebral cortex. In addition, these techniques locate the location of dysfunctional brain areas in two areas of the left hemisphere: the parieto-temporal region and the temporo-occipital region (Matute, Ardila and Roselli, 2010).
In addition, compensatory mechanisms are found related to areas near the lower frontal rotation of the two hemispheres, in addition to the right occipital-temporal region , related to word recognition (Matute, Ardila and Roselli, 2010).
What are the effects of dyslexia?
The impact of the specific reading disorder is different for each person and depends largely on the severity and specific interventions that are being made. The main problems that people with dyslexia present are difficulty with word recognition, reading fluency. and in some cases difficulty in spelling and writing (International Dyslexia Association, 2016).
In many cases, it can also present problems in expressive language even if they are exposed to good language models in their family and school contexts beforehand. There may be difficulties in expressing oneself clearly or in understanding the totality of messages issued by other people (International Dyslexia Association, 2016).
Although on several occasions it is difficult to recognize or identify some of these language problems, these can trigger important consequences at school, work or in social relationships. In addition, it can also affect the person’s own image, many students come to feel less capable, underestimating both their abilities and their potential abilities (International Dyslexia Association, 2016).
What cognitive and linguistic components does dyslexia affect?
The analysis of the neuropsychological processes involved in the development of dyslexia, we must make reference to comorbidity level. In general, reading disorder is very often associated with the disorder of calculation or written expression. Therefore, they will share common characteristics and also relate to problems in the socio-emotional area (demoralization, low self-esteem, efficiency, etc.) (Matute, Ardila and Roselli, 2010).
In addition, if we refer to the etiological diagnosis, dyslexia can appear associated with medical illnesses, so that cognitive and linguistic difficulties will be associated with the syndrome in question (Matute, Ardila and Roselli, 2010).
In relation to the cognitive components involved in dyslexia, a large number of theories have been proposed that involve deficits in rapid auditory processing, in visual processing, in cerebellar participation, automation deficit, magnocellular system deficit, in processing of temporary order or motor deficits. However, phonemic awareness now to be the clearest predictor of the reading skills (Matute, Rosselli and Ardila, 2010).
In addition, there are also other cognitive and / or linguistic functions that are related to learning to read: ability to decode visual stimuli, speed of naming, amplitude of vocabulary, capacity of working memory, attention capacity and concentration (Matute, Ardila and Roselli, 2010).
When is a child considered to have dyslexia?
The diagnostic criteria included in the Diagnostic and Statistical Manual of Mental Disorders IV refer to the following conditions:
Criterion A : performance in reading (ie, accuracy, speed and reading comprehension assessed by standardized tests administered individually) which is substantially below the expected function of chronological age, IQ and schooling own of the age of the individual. Oral reading is characterized by distortions, substitutions or omissions; Both oral and silent reading are characterized by slowness and errors in comprehension.
Criterion B : alteration of reading significantly interferes with academic performance or certain activities of daily life that require
Criterion C : if a sensory deficit is present, reading difficulties exceed those usually associated with it. If there is a neurological or medical disease or a sensory deficit, they should be coded in Axis III.
Is it possible to treat dyslexia?
Dyslexia is a type of disorder that will occur throughout the life of people who suffer from it. With an efficient intervention, in many of the cases they develop an optimal learning of reading and writing (International Dyslexia Association, 2016).
Early identification and early treatment is essential to achieve deficit control and successful adaptation to the different academic levels .
In many cases, the intervention of a specialized therapist who uses different multisensory strategies for working with reading difficulties will be required. It is important that the intervention be carried out through a systematic method that involves several senses (International Dyslexia Association, 2016).
Students with dyslexia often require repeated feedback and a high amount of practice to develop correct and effective word recognition skills (International Dyslexia Association, 2016).
Academic modifications are frequently applied to facilitate curricular success. Students with dyslexia usually require a longer time to complete homework or note-taking aids (International Dyslexia Association, 2016).