Dyslexia, or “trouble with reading,” can have many underlying causes. There is consensus that the underlying cause of dyslexia for many individuals is phonological processing. Phonological processing is the ability to use language sounds to process spoken and written language. If an individual can’t discriminate between similar sounds, for example, or reliably produce language sounds, that is likely to significantly impair the development of reading skills.
At the same time, many individuals with dyslexia also have weaknesses in other cognitive processes, including attention skills, verbal working memory, processing speed, inhibitory control, and long-term memory. Thus, it is a complex condition with many variations.
Attention skills, especially selective attention (or the ability to screen out irrelevant information, can hamper reading. When a student is attempting to read, and their attention is diverted by irrelevant information, the available space is working memory is filled in with that irrelevant information. This may make it impossible to identify a word since the accurate, relevant information is crowded out or confused by inaccurate sound and letter information. Anxiety can exacerbate this issue.
Verbal Working Memory
Verbal working memory is the ability to hold verbal information in conscious thought. Working memory is limited for everyone, but working memory deficits can be directly related to difficulty in reading. particularly in being able to hold sufficient information to make sense of what is being read. The need to figure out letter-sound correspondences and remembering the letters already identified can tax students with verbal working memory deficits.
When working memory is more limited than typical, the letters/phonemes that first reach working memory may have begun to fade by the time subsequent letters/phonemes arrive so that that there are gaps in words and phrases that do not allow them to reliably interpreted. Slow processing speed can also make it more difficult to recall even high quality information from long-term memory.
Inhibitory control refers to the ability to stop from doing something we otherwise would do. Weak inhibitory control can result in “blurting” out incorrect words. With adequate inhibitory control, word candidates are selectively suppressed.
When sounds and words are encoded inaccurately or incompletely in long-term memory, a student’s ability to recognize and retrieve information is affected. There may be multiple instances of different sounds/letters related to the same word resulting in confusion as to what the word actually is.
Many students with dyslexia benefit from building up these underlying cognitive processes through cognitive training.