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Dyslexia and Working Memory

What's the link?

Case Study: "My son David is 10 and he is very bright, but his main problem is his difficulty in writing things down. He says the problem is finding the words, especially the first word. He takes forever to write down a very short story, and is usually disappointed with it because he has a much more complex vision of the story in his head (like a movie) but cannot get to the words to write it down. The less processing is involved, such as figuring out where to start and which details to include, the quicker he can write. For example, writing down a set of instructions for how to make a sandwich would be done faster than a story (still slower than average). He is very quiet in groups, cannot take in more than a few verbal instructions at once, often forgets what he is sent to do, often fails to start a task until reminded, often seems to be daydreaming, and has problems organizing himself to do something. He drives me and his teacher mad with the need for constant reminders of what he is supposed to be doing."

Students with dyslexia, like David, have very poor verbal (auditory) working memory and they have difficulty remembering the sequence of information that is presented out loud, such as instructions, new vocabulary words, and even names. Their poor verbal working memory means that they have a hard time repeating new or unfamiliar verbal information. This can make them embarrassed to repeat information in front of others.

It takes considerable working memory space to keep in mind the relevant speech sounds and concepts necessary for identifying words and understanding text, which can exceed the capacity of the student with dyslexia. Thus, the combination of processing and remembering verbal information, rather than just remembering information, is very difficult for the individual with dyslexia. This happened to David when he was writing his story: the more information he had to process when writing the story, the longer it took him to complete the activity.

When it comes to writing, students need both verbal working memory and phonological awareness skills to blend the phonemes of a word, combine words to make a meaningful sentence, and finally remember what they want to say in order to write it down. David struggled to translate his visual image of a story to paper because his working memory was not big enough to combine these elements and then translate it to paper.

There are several reasons why students with reading difficulties have such poor verbal working memory skills. One explanation is that they have difficulty in repeating the information fast enough to remember it. Most of us rehearse information to prevent memory loss, at least until we get a pen and paper. The speed with which we rehearse information is linked to how much information we can hold in working memory. However, it takes the individual with dyslexia much longer to repeat phrases and, as a result, they can run out of time to rehearse all the important information. Here is an example: If you give your class a list of five things to do on their way back to their desk, the student with dyslexia may only have time to repeat two of those five things, and thus be more likely to leave some of the tasks unfinished.

The way in which they rehearse information is also important: the student has to repeat all the information in the correct sequence, starting from the beginning of the list to the end. However, the student with dyslexia is unlikely to repeat information this way. Let’s go back to the example of the five instructions: the student with dyslexia will start rehearsing from the end of the list and consequently they tend to forget all but the last bit of information they heard.

Students with dyslexia have strengths in visual-spatial working memory. Studies comparing visual memory for novel objects confirm that students with dyslexia perform similarly to normal readers. However, if students with dyslexia are asked to label the objects, their performance drops because they have to rely on verbal working memory. Their good visual working memory means that they learn words as a unit, rather than work out their individual sounds.

This strategy can be quite useful initially as they build up an impressive mental look-up table. But they usually find new words very difficult, as they do not have the skills to match the sounds to the letters to decipher them. For example, they may be able to quickly read the word “hawk” if it was part of their lookup table, but the word “tomahawk” would be hard to read if it were unfamiliar to them.

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