NEURAL PROCESSING OF WORDS IN THE HUMAN EXTRASTRIATE VISUAL-CORTEX

Measurements of neuromagnetic fields were made for the responses to vi sually presented words comprised of Japanese characters (phonograms), and for comparison of responses to single characters and character sym bols, while subjects performed, respectively, semantic category matchi ng, rhyming, and character matching tasks. The magnetic field response s recorded from the occipital and occipitotemporal regions consisted o f 2-3 major peak components, occurring between 150 and 300 ms after th e onset of the visual forms. The localization of equivalent current di pole sources of these components within the brain structure of individ ual subjects indicated that the main regions of the neural activity oc curring at 150-250 ms were located in the extrastriate visual cortices . They included the lateral area mostly at the occipital gyrus, medial area consisting of parieto-occipital and calcarine sulci and lingual gyrus, and ventral area which is continuous from the lingual gyms (LG) to fusiform gyrus (FG). In the ventral LG/FG area the left side was a ctivated primarily by words, while the right side was responsive in mo re or less equally to words, characters, and symbols. It is suggested that the left occipitotemporal LG/FG mediates the neural function that subserves the specific visual word processing and/or general analysis of complex graphical features of visual forms. (C) 1998 Elsevier Scie nce B.V.