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There is a PowerPoint file available to accompany this presentation. The BDA Conference 2001 CD-ROM contains 61 PowerPoint files. For details of how to obtain the CD-ROM, please contact the BDA.
Thursday stream 1 Session 09.00 - 11.10 Length 25 minutes
R. D. Milne , M. C. Corbalis and T. Nicholson
(1) Department of Psychology, University of Auckland, (2) School of Education, University of Auckland rd.milne@auckland.ac.nz
Abstract
Using high-density EEG recording, brain activity was studied in adult dyslexics and normal controls while they carried out a lexical-decision task. There were 5 dysphonetic dyslexics, 5 dyseidetic dyslexics, and 10 matched controls. We found that (1) controls showed a positive correlation between the ratio of anterior to posterior beta asymmetry and performance on the task, (2) dysphonetics showed higher beta power in anterior relative to posterior regions, and (3) dyseidetics showed higher beta power in posterior relative to anterior regions. According to the dual-route theory of reading, there are two strategies that can be used in lexical decision. A visual strategy involves visual word identification and direct access to a visual lexicon. In contrast, a phonological strategy involves grapheme-to-phoneme conversion and access to a speech output lexicon. It is suggested that the relative increase in frontal beta activity in phonological dyslexics may reflect under-utilization of the auditory strategy, including grapheme-to-phoneme conversion. In the dyseidetic group, by contrast, increased posterior beta activity may reflect activity in the pathway involving access to the visual input lexicon.
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