Some dyslexic individuals have trouble encoding regularities in repeated sets of sounds, reports a study in the December 2006 issue of Nature Neuroscience.
Developmental dyslexia is a common condition characterized by difficulty in the acquisition of reading skills. The root cause of dyslexia remains controversial, but is believed to involve impairments in processing the sounds that make up language, which may be a necessary step in determining the meaning of words. Consistent with this hypothesis, dyslexics perform poorly compared to non-dyslexics on many auditory tasks.
Merav Ahissar and colleagues report that a subpopulation of dyslexics, those with learning disabilities, cannot use sound repetition to their advantage in auditory tasks. Dyslexic subjects performed as well as control subjects on two auditory discrimination tasks when sound stimuli were drawn from a large set. When the stimulus sets were small, the performance of the control subjects improved, presumably because they could use the regularities to help them perform the task. Dyslexic subjects, in contrast, failed to benefit from small stimulus sets involving sound repetitions, performing much worse than control subjects under those conditions.
The authors suggest that this might be because dyslexics are unable to form a memory trace of the repeated stimuli. Whether this impairment generalizes to dyslexics who are not learning disabled, and whether it is causally related to reading difficulties, requires further investigation.
Merav Ahissar, (Hebrew University, Jerusalem, Israel)
Abstract available online.
(C) Nature Neuroscience press release.
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