| |
Abstract:
Research with healthy subjects suggests that EEG theta
activity reflects the encoding of new information whereas upper
alpha desynchronization reflects semantic processes. Are these EEG
responses reduced or changed in dyslexics? A sample of normal and
dyslexic subjects performed a number, word and pseudoword reading
task. The EEG was analyzed in 6 different frequency bands (of 2 Hz
width), covering a frequency range of about 4 - 16 Hz. A phasic
response in event-related band power (ERBP) was measured in terms
of an increase or decrease in band power during reading with
respect to a reference interval. In the theta band, dyslexics show
a complete lack of a phasic response at occipital sites
particularly during pseudoword processing. For the different alpha
bands, the most significant finding was a pronounced upper alpha
desynchronization for dyslexics over left frontal recording sites.
A highly selective finding was obtained for the beta 1b band (14-16
Hz). Over sites that correspond to Broca's area and the Angular
Gyrus, only normals show a highly signifcant desynchronization
during the processing of words. We conclude that dyslexics (i) fail
to encode words and pseudowords in visual working memory, (ii) show
more effort in the semantic processing of words, and fail to
activate Broca's area and the Angular Gyrus.
|
