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Abstract:
Deficits in phonological skills appear to be at the heart of
reading disability, however, the nature of this impairment is not
yet known. The hypothesis that dyslexic subjects are impaired in
auditory frequency discrimination was tested using mismatch
negativity (MMN) while subjects performed a visual distractor task.
In separate blocks MMN responses to graded increases in tone
frequency (deviance of 15, 30, 60, 90Hz, standard 1kHz) or tone
duration (deviance of 40, 80, 120, 160ms, standard 200ms) were
recorded in ten dyslexic and matched control subjects. MMN to
changes in tone frequency but not to changes in tone duration were
reduced in amplitude and prolonged in latency in dyslexic subjects.
This was corroborated by a similarly specific impairment in
discriminating tone frequency, but not tone duration, which was
assessed separately. Furthermore, the pitch discrimination and MMN
deficit was correlated with the degree of impairment in
phonological skills, as reflected in reading errors of regular
words and non-words. It is possible that in dyslexia a persistent
sensory deficit in monitoring the frequency of incoming sound may
impair the feedback control necessary for the normal development of
phonological skills.
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