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Brain differences of dyslexics
What exactly goes wrong in the brains of dyslectics? While reading the eyes see the letters and words. They are signaled to the visual cortex in the brains. Here the shapes of the characters are identified.
For example: does the character have two sticks, at which side is the curve, is it a capital or not? Then the information is transferred to the hindmost language area out of three in the brains. Here, all the words you hear or pronounce are swiftly processed.
In dyslexic children the same process occurs, but a bit slower. Scientists disagree on whether that process takes place in only the left brain half or in both halves. The origin of dyslexia is found in an abnormal development of the language areas in the brains or cooperation among them. There are problems in converting phonemes (sounds) to graphemes (language characters, such as letters). As a result, dyslexic children are more influenced by noise around them.
Phonological deficit
Researchers have looked for many biological factors that explain dyslexia, but so far it is seen as a phonological deficit. A phonological deficit means that dyslexics have a neural variance in the processing of the sound structure of speech. There is no clear evidence that a phonological deficit leads to a reading problem. The link between characters and sounds could be the missing part in the brains. Due to the disturbed phonological processing it is more difficult to learn the connection between letters and sounds, and then use them for reading.The link between letters and sounds
Scientists have investigated where and how letter-sound links are made, by scanning the brains of
well-reading students. This way, they could determine which brain areas are used for pronouncing
letters. A certain area of the brains, the planum temporale (PT) shows higher activity for a correct
word than for a nonexistent word. This area was inactive when the subjects only looked at the letters,
whereas the letters do affect the processing of speech sounds of letter-sound combinations. Correct
letters led to increased activity and incorrect letters to lower activity.The superior temporal sulcus (STS, marked red in the temporal lobe, see figure) showed more response to the letter-sound combinations than to separate letters and sounds. Unlike the PT, the STS showed activity when the subjects looked at letters and listened to sounds at the same time. This means that the STS connects letters and sounds. Evidently, the STS determines whether a letter and a sound match, and sends this information to the PT. If the letter and sound match, the processing of speech sounds is enhanced by the PT, otherwise the PT weakens the activity.
Currently, researches are in progress to the link between letters and sounds as the missing part in dyslectics. So far, the studies indicate that the letter-sound system in dyslexics is not well developed.