Evidence has been growing in recent years that dyslexia, the reading and writing impairment that affects around 5% of the population, may actually have more to do with sound than with sight. Now Michael Merzenich of the University of California, San Francisco, and colleagues add to this evidence the observation that some adult dyslexics, although otherwise normal, seem less able to process streams of short, rapidly changing sounds than do non-dyslexics. This may hinder their appreciation of the nuances of speech and thus interfere with language learning.
This deficit, which Merzenich?s team report in Proceedings of the National Academy of Sciences (24 May 1999) is thought to arise in the auditory cortex - the region of the brain that acts as the main gateway for incoming acoustic information. Using ?magnetoencephalographic? imaging to monitor, with millisecond precision, the magnetic fluctuations caused by localised neural activity, the researchers found that activity in the auditory cortex was weaker and slower to get going in seven dyslexics challenged with quick-fire sound sequences than it was in control subjects performing the same tasks.
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