Defining dyslexia

Nowadays, dyslexia is defined as a specific learning disability with a neurobiological origin. It causes difficulties with the accurate and fluent recognition of words, is characterized by poor spelling and impairs decoding abilities. This symptoms often result in a deficit in the phonological component of language, which is often unexpected in relation to other cognitive abilities. Therefore, dyslexia has also been called ‘the unexpected difficulty in reading’. This means that a child who possesses all factors necessary to be a good reader, such as intelligence and motivation, still struggles.

To measure dyslexia as a unexpected difficulty, IQ and reading achievement were compared to look for a discrepancy between those two. Unfortunately, this means that in real-life children often had to fail before they got diagnosed and received help. Therefore this was also called the wait-to-fail-model. Alternative approaches were needed. One such an approach focuses on a more dynamic assessment, which is also applicable to early grades and therefore early recognition. The ongoing development or fluency in component reading skills such as letter recognition is measured frequently and compared with expected norms. Another approach provides all children with a evidence-based reading instruction and frequently monitors their progress. Children who do not make any progress are selected to receive additional support. This is called the response to intervention.

Recent data has suggested that reading difficulties occur as part of a continuum that includes nonimpaired as well as disabled readers. This also includes dyslexia, which therefore seems to occur in degrees of severity. This dimensional model also suggests that cut of points may be implemented to define groups but only differentiate in degree, not kind. These arbitrary points thus may haven no biological validity. Given these findings, children who do not meet these arbitrary criteria may still require and profit from some help.

Epidemiology of dyslexia

Dyslexia is highly prevalent, though exact numbers depend on the definition and cut-off points established as criteria. There is a string misbelief that reading problems are outgrown or represent a developmental lag. It is important to address reading problems expressed early in life, otherwise they will persist with time. Furthermore, research shows a much better response to interventions provided in the first years of school compared with those presented in the later years of primary school.

A lot more boys than girls get diagnosed with dyslexia. This seems partially due to the often more disruptive behavior of boys in the classroom, which leads to earlier recognition through the traditional school identifications. Mostly, girls are more quit but they may struggle with reading on their own. The identification of dyslexia should not rely on behavioral difficulties. Using ‘response to intervention’ could prevent this.

Phonological awareness

The language system is a hierarchy of different modules, starting with the phonological module, which is dedicated to processing the fundamental units of language: phonemes. We consider language to be generative, since it can produce thousands of words out of just 44 phonemes (in the English language). The phonological module assembles the phonemes into words for the speakers, and disassembles the words into phonemes for the listener. Coarticulation is the term used to describe the process of different segments sounding seamless to the listener. The fact that spoken language doesn’t give any clue to its underlying segmental nature can be a challenge for the reader-to-be.

Spoken language is innate, whereas written language is acquired and must be taught. The literature suggests that the prime challenge for beginning readers is to link the letters to spoken language: the phonemes. Therefore this should serve as the major focus of early reading instruction.

The core of reading is the ability to identify, recognize and manipulate syllables and phonemes within spoken language. We refer to this as phonological awareness (PA), what also seems to be the core of reading difficulties. Reading acquisition can be predicted by PA, it differentiates good and poor readers and instructions with the intention to improve PA improve reading. Children first develop an awareness to words as a whole, followed by syllables and then phonemes: phonemic awareness. Research suggests that reading itself is necessary for developing PA, and emphasis the importance of reading instruction to the development of this critical skill.

Alphabetic orthographies use letters and clusters of letters in order to produce phonemes and words, where logographic orthographies use characters (like for example in China and Japan). Dyslexia occurs in both orthographies. Children learn to read words more accurately when the letter-sound mappings are very consistent, like in the Italian language where there’s a great predictability of sound-symbol linkages. Variations in consistency will influence the expression of dyslexia across different languages. In consistent orthographies it is relatively easy for good readers as well as dyslectics to learn reading words accurately. Therefore, dyslexia may only just be recognized until later on in school because only reading fluency is affected while reading accuracy is relatively intact. Spelling may be effected because dyslectics have trouble with inconsistencies between sound and spelling.

Etiology

Dyslexia appears to be inheritable, interestingly enough especially in in children with high IQ’s. Nowadays, half of the variance in dyslectics can be explained by genetic factors while the rest can be attributed to environmental factors. Taking this information into account, children from dyslectic parents or with dyslectic siblings should be considered at risk for developing dyslexia. Therefore they should be carefully observed for signs of reading difficulties. It’s important to emphasize that a genetic aetiology doesn’t mean that interventions do not work for this group of children. They can still benefit from evidence-based intervention and deserve this extra help.

By using neuroimaging technology, neuroscientists have been able to identify several interrelated neural networks of reading in the left hemisphere (for example Broca’s area). Functional brain imaging studies have shown deficits in the left hemispheres of disabled readers, explaining their reading difficulties. Nevertheless, they seem to have developed compensatory systems in both hemispheres. Several studies have shown that neural systems for reading can be improved and influenced by reading interventions. The way children are taught can foster the development of those automatic neural systems that serve skilled reading, so teaching matters. It is still necessary to determine the precise relationship between types of interventions, changes in brain activation and clinical improvements.

Studies using fMRI have indicated that dyslexics are not able to use sound-symbol linkages growing into adulthood, and start to rely on memorized words. By reading words from memorization, familiar words are recognized and easy to read but they show difficulties reading unfamiliar words. This is a problem because memory has limited capacity. The fMRI scans showed linkages between reading systems in the left hemisphere in non-impaired readers, while linkages between the left hemisphere and neural systems associated with memory in the right hemisphere were found in poor readers.

The diagnosis and treatment of dyslexia

Phonological processing isn’t only critical to written language, but also greatly influences spoken language. Therefore, although they may be more subtle, children with dyslexia can also show problems in spoken language. Furthermore, the clinical picture of dyslexia consists of reading problems, difficulties in handwriting and spelling, problems with mastering a foreign language and attentional problems. Reading fluency can be severely impaired in individuals with dyslexia thereby tremendously draining attentional resources. This makes attention a secondary problem next to the primary reading problems. On the other hand, dyslexia is highly comorbid with ADHD, which makes it a primary problem in some cases. In contrast to all those impairments, other cognitive abilities are usually intact.

Dyslexia is a clinical diagnose, best made by a trained clinician who uses history of the child, observes the child while reading and administers a battery of tests that assess the child’s cognitive abilities.

Effective reading instruction should include five essential elements, namely phonemic awareness, phonics, comprehension, awareness and fluency. These skills have to be taught systematically and explicitly. Early interventions for children with dyslexia have shown to be very promising in many studies. Classroom interventions, pullout remedial approaches and combinations of those two can improve phonological processing and initial word identification skills. Prevention programs that specifically focus on phonemic awareness, phonics and the meaning of text in the earliest stages of reading instruction reduce the base rates of at-risk students. Interventions for older students unfortunately show less promising results. It appears to be quite difficult to bring children or adults up to the expected grade levels once they fall behind, although significant improvements are still possible. Many studies have proven phonologically based decoding and word recognition to be teachable aspects of reading for most individuals. This evidence indicates that focused, intense, systematic and explicit interventions can positively impact word-reading development.

To increase fluency, fluency programs use repeated reading of connected text. More recent programs also focus on building semantic knowledge and orthographic pattern awareness. When these skills are improved, less strategic attention on the act of reading is necessary as it becomes automatic and therefore the reader can direct more cognitive energy and focus on comprehension and meaning.

Reading comprehension can be enhanced by strategy-related programs, which teach critical thinking skills related to understanding text and constructing its meaning based on the prior knowledge of the reader. The programs focus on finding ideas and facts, developing multiple meaning of words, summarizing text and increasing vocabulary. Unfortunately, applying those strategies in comprehension situations and new text reading has found to be a less consistent.

Although treatment plans can have a lot of positive effects, not all dyslexics respond to these programs. The dyslexia population is heterogeneous and there is no remedial instruction program that will cover the needs of all poor readers.

In order to help children with dyslexia to perform better at school, accommodations in the classroom are necessary. These accommodations occur in three different types:

1. Providing information through an auditory made, thereby by-passing the reading difficulties

2. Providing compensatory assistive technologies, such as computers

3. Provide students with additional time so that they can demonstrate their knowledge despite of dysfluent reading.