This type of dylexia is a result of brain trauma, such as a stroke , or large scale injury to the head in the area that controls reading and writing functions. This particular sub-category of dyslexia is rarely seen in school-age children, being more common in adults, though overall remains extremely rare.
Peripheral alexia is closer to 'typical' dyslexia, whereas central alexia encompasses both alexia and aphasia (loss of previous speaking ability).
Peripheral alexia is closer to 'typical' dyslexia, whereas central alexia encompasses both alexia and aphasia (loss of previous speaking ability).
Types of Alexia, or Trauma Dyslexia
Peripheral AlexiaHemianopic AlexiaHemianopic alexia is said to be caused by damage to the primary visual cortex, affecting the visual field. Someone with this imparement may read text at a slower pace, though s/he will be able to read single words almost normally. Patients with hemianopic alexia will often have abmormal eye-movements, and a study of PET scans shows that they do not have normal activity to the right frontal eye field.
There are a couple ways to go about rehabilitation. Some of the visual function can be regained by retro-chiasmal lesions, though evidence suggests that this will only provide partial recovery of vision. Another option is the use of moving text to encourage improvements in reading. Text scrolls across the screen from right to left, and the individual reads the text aloud. This had proven to increase the speed of reading, and the results persists even when the individual returned to reading stationary text. Pure Alexia and Global AlexiaPure alexia is one of the first idendified forms of peripheral alexia, though there is rising evidence that suggests it may not be as 'pure' as was first thought. Patients with pure alexia will usually be able to recognize individual letters, but will have difficulty reading single words. However, many will also display difficulties with processing numbers, or other non-linguistic stimuli. There is also a greater difficulty withreading when the word length increases.
There is also rising evidence that says that patients with pure alexia do often have difficulty identifying letters, particularly those that look alike, such as i, j, l. At the severe end of this, when several additional secconds are needed per each letter added to a word, pure alexia morphs into global alexia. This is the most severe form of peripheral alexia. Patients with global alexia either cannot recognize individual letters or make errors in attempting to name them, even though they may write almost normally. These patients may have other language difficulties and may stand on the thin line between peripheral and cental alexia. Patients with pure alexia are rare enough that allthough patients are evaluated, it is on an individual basis, and no standardization of treatment has been done. One of the simplest methods is to have patients read aloud a collection of words repeatedly. This has produced a tentitively positive effect: patients had an improvement in their reading of longer words without sacrificing accuracy after completion. Another strategy is to have patients trace out the letters of the words they are reading. Again, this has shown a tentivitely positive effect, though this particular method may be better suited to those patients at the slower end of this spectrum. Global alexia is much more severe, and unfortunately there had not been a reported case ofa patiend successfully rehabilitated. Other Types of Peripheral AlexiaThere are two smaller branches of peripheral alexia.
Neglect alexia is a lesion on the right parietal lobe. Patients with neglect alexia have a visual imparement to one side, and the use of prism glasses aids patients in encouraging focus on the neglected side and helping to correct reading issues.This is not a long-term rehabilitation method, and patient will often have to go back and reinforce the therapy once in a while. Patients with attentional alexia will often complain of letter crowding or migration, and will sometimes blend parts of two words into one. There are fewer issues when words are presented alone as compared to being next to other words or letters. Use of a large magnifying glass can possibly help the crowding of words in a sentence, but no therapy or rehabilitation had been proven. |
Central AlexiaPhonological Alexia and Deep AlexiaPatients suffering from phonological alexia can read familiar words fairly normally. They have a difficult time with new words, including legal terms; this is in part because they are unable to sound to the word to learn it. They require repeated exposure to acquire the ability to retain and recognize words.
There are treatment options for this, one approach being to pair the new word with a word that sounds similar (such as be paired with bee) or with a word sharing an initial phoneme (suck as pairing much with mud). This has been met with some success, though personalization of this or another treatment option may still be necessary. Patients that suffer from deep alexia have many of the same appearances of phonological alexia, but they also make semantic errors (such as reading cat as dog). A patient may read the word off as on, and be unable to read the word of at all. Treatment for deep alexia is tricky. Approaching it by giving a patient a set of words that have a personal meaning and having them read through them repeatedly, while writing the key words down had met with some surprising results, and though reading of them increases noticeable it usually doesn't generalize out to untrained words. Surface AlexiaSurface alexia is the opposite of phonological alexia. Though non-words can be read easily, irregular words such as colonel cannot be read.
The best treatment for this is to pair the word with a picture or other mode of identifying it to increase the chances of the word's pronunciation being retained. This works best when words that have a direct effect on the patient's life are involved, though it is unlikely that this can be broadened to encompass untrained words. |