home . search . contact   index by author chronological index

- abstract below
- a PowerPoint presentation is available on the conference CD.
For details of how to obtain the CD, please contact the BDA.

Cortical dynamics of visual word recognition: An MEG study

Piers Cornelissen , Kristen Pammer, Ian Holliday , Peter Hansen

(1) University of Newcastle, UK; (2) Oxford University, UK; (3) Aston University, UK p.l.cornelissen@ncl.ac.uk

Abstract

Skilled reading utilizes a highly organized cortical system involving an anterior (fronto-temporal) and two left hemisphere posterior reading circuits; one dorsal (temporo-parietal) and the other ventral (occipito-temporal). However, there is no clear understanding of the dynamic nature of information flow through the network. In this study, 10 normally reading adults carried out a lexical decision task while cortical responses were recorded with MEG. Signals were analysed for each individual using SAM in overlapping time windows up to 500msec and overlapping frequency bands up to 50Hz, with a reference period of 200msec pre-stimulus onset. Group random effects maps were generated using SNPM. Within 200msec of seeing a word, activity is restricted to primary visual cortical areas together with bilateral BA 18/19, consistent with the extraction of visual features within a retino-topic framework (Tarkiainen et al, Brain 2002). Between 200-400msec, there is parallel, but transient activation of left hemisphere cortical areas associated with phonological processing (IFG, BA 44/45), semantic processing (anterior MTG, BA 21) and fusiform gyrus (VWFA) together with inferior temporal gyrus (BA 37). Starting around 200msec, activity also begins in left posterior MTG (BA 37/39) peaking around 300-550msec. The early BA 37/39 activity is accompanied by co-activation in angular and supramarginal gyri (BA 39/40) and the superior temporal operculum. Posterior MTG, supramarginal gyrus and the angular gyrus may play a role in cross-modal association. We suggest therefore that the posterior temporo-parietal regions that are activated between 300-550msec are cross-modal association areas for the convergence of orthographic, phonological and semantic information represented earlier in a parallel-distributed network, thereby modulating the sequence of later activity in anterior fusiform gyrus.

Disclaimer: all the abstracts presented here have satisfied the academic committee as appropriate for presentation at an international conference. However, the material reflects the views of the authors, not necessarily those of the academic committee or the BDA. No endorsement of any approach, product or service is intended or implied.

home . search . contact . index by author . chronological index