Developmental Dyslexia
Some children find it very difficult to learn to read. Despite having normal intelligence, they still read very slowly and with many errors, and these problems persist even after they become adults. Their reading improves with practice, but less than that of their peers. This persistent reading difficulty is called developmental dyslexia, and it is still unclear what causes dyslexia. However, it has been found that dyslexic patients benefit less from the repetition of sounds than those without dyslexia, and they act less familiar with common syllables and word structures. Using brain scanning equipment, it has also been found that dyslexia patients’ brains forget faster. This article contains information about the causes of developmental dyslexia and reading difficulties.
Learning to Read Process
Reading is the process of converting written symbols (such as English letters) into a series of sounds that are meaningful words. When children first start reading, they need to learn the sounds of the letters sequentially to read the words, and then, after gaining experience, they begin to define whole words. The representations and meanings of spoken words are present in the minds of children before they start reading. This is known because children can understand and speak the spoken language long before they learn to read. Most children learn to read by the age of 6-7, but this skill continues to develop as children grow and become more productive.
Dyslexia Patients and Reading Efforts
For some children, learning to read is not easy and can even be very frustrating. Approximately 7% of children in regular schools have very difficult to learn to read, although they do not have special vision or hearing problems and have normal intelligence. These children are born with this challenge and stay with them even when they are adults. This difficulty with reading is a learning disorder called developmental dyslexia. People with developmental dyslexia read slower and with more errors than those without dyslexia. Usually, people with dyslexia also make a lot of spelling mistakes, but apart from problems with reading and spelling, their abilities in other areas (such as math) are usually completely normal (unless they have another disorder).
Reading is a complex process that involves vision, hearing, memory and eye movements. Given that all these things are not harmed in dyslexic patients, it is odd that they still have such difficulty reading. It seems that despite the specific characterization of dyslexia, people with dyslexia have additional difficulties in reading and writing and even in language use that go beyond their limits.
When learning to read (or reading unfamiliar words), the sounds represented by the letters are combined into one word. When it is necessary to write a heard word, it is divided into speech sounds and translated into letters. Basic speech sounds are called phonemes. Because people with dyslexia experience difficulties in the process of separating and combining phonemes, many researchers assume that the mental representation of basic language sounds is impaired in dyslexia. About 40 years ago, researchers suggested that the difficulty in dyslexia lies in the ability to process sounds and is not language specific. Experiments are designed to better understand this concept.
Does Dyslexia Cause Old Information to Be Forgotten Faster?
A number of experiments have been conducted over the past 15 years involving children, adolescents and adults with dyslexia. A typical experiment consists of dozens of steps, and at each step the participant is played two sounds with a short interval (about one second) between them. The participant is asked to decide which voice has a louder, first or second pitch. In these types of experiments, participants feel they are comparing two sounds, and that is how they decide. However, it turns out that voices from previous steps also influence the decision: the inner representation of the pitch of the first sound in the current step becomes similar to the previous sounds heard in the previous steps. For example, if a high pitched sound is heard, most of the previous sounds are low pitched, the representation of that sound will be slightly lower, pulled down.
It was found that this effect was smaller for participants with dyslexia. Subsequently, it is assumed that dyslexic patients have difficulty properly storing the sounds they hear in memory. This type of storage is essential for efficient reading. Another experiment was conducted to test the hypothesis that voice memories decay faster in the brain of dyslexia patients and to understand in which brain regions this faster decay occurs. In this experiment, participants were scanned in a device called a functional magnetic resonance imaging scanner (fMRI scanner).
In general, when the same sound is presented twice with a short space between them, the brain’s response to the second presentation is smaller. This phenomenon is called neural adaptation. The smaller response to the second sound suggests that the brain somehow still remembers the first sound because the first sound still affects the processing of the second sound. They found that in people with dyslexia, this subconscious memory period of the first sound was shorter. When the gap between sounds is 10 seconds, the response to the second sound measured in the brains of people without dyslexia is smaller, indicating that the memory of the first sound is still stored in their brains. On the contrary, people with dyslexia give a full intensity response to the second sound if the sounds are 10 seconds apart. This indicates that their brains no longer have the memory of the first sound, and this difference in memory time is from the cortex.
Dyslexia Patients Learn Repetitions Slower
The main problem most people with dyslexia face is reading words. For people with dyslexia, it is possible that rapid memory loss can slow their knowledge. In general, the more exposure to something, the better its performance in tasks related to that exposure. However, for people with dyslexia, the learning curve to things they’ve been exposed to before is slower.
Effects of Morphology in Dyslexia Patients
Language is used throughout life, and most people learn language rules and structure automatically and unconsciously. In the experiments, rules about the structure of the language and how the word parts are put together were used and this was called morphology. In Hebrew, all verbs have one of several specific structures and all other forms are illegal in the language, so readers will never encounter these non-existent forms. For example, the word lagadnu is not a true word in Hebrew, but is very similar in structure to the true words katavnu, pagashnu, and kalatnu. On the other hand, the word hukshimti is not a true word in Hebrew either, but unlike lagadnu, there are no Hebrew words that share its structure, so local Hebrew readers are less familiar.
When the reading speed was examined whether it was affected by familiarity with word morphology, it was determined that students without dyslexia read fake words with a structure similar to real words faster and more accurately than they read words without a familiar structure. This is expected because words with a familiar structure require less work in the brain (they do not need to be processed letter by letter.) However, for students with dyslexia, there is no significant improvement in reading speed or accuracy of made up words with Hebrew morphology compared to words that do not have a familiar structure. . These results show that morphology does not help people with dyslexia in reading as well as helping people without dyslexia.
Similar results are obtained when words are used in smaller units. Words are built from syllables. It is known that the syllable frequency has a great effect on the success rate when the participants are asked to repeat the syllable sequence presented to them. Correspondingly, the participants in the experiments reproduced frequent syllable sequences more accurately than less frequent syllables, but this advantage of syllable frequency was significantly less for participants with dyslexia. These results show that the syllable frequency does not improve the memory of people with dyslexia as well as the memory of people without dyslexia. Therefore, people with dyslexia benefit less from repetition of syllables and word structures, similar to how they benefit less from repeating simple sounds. And as a result, their performance isn’t as good as people without dyslexia. The exposure of participants with dyslexia to syllables and words is similar to those of participants without dyslexia, but participants with dyslexia gain less from this prolonged exposure.
Developmental dyslexia is a special learning disorder that prevents the acquisition of reading skills. Researchers have been investigating the cause of dyslexia for years, and it has been suggested that the main difficulty in dyslexia is the less efficient use of previous knowledge on previously presented stimuli, due to the faster memory impairment from these stimuli. This idea is based on the results of experiments with simple sounds and brain activity. Also, the accuracy of reading words with and without a familiar structure; compare its speed with the memory of frequent and sparse syllables. These data help understand the cause of dyslexia, and understanding the cause can eventually aid treatment.
