Microstate analysis of information processing in a reading task with Kanji and Katakana

Abstract

The present study investigated the differences in time course and the brain electric signature during the reading process of two types of Japanese characters, Kanji (morphograms) and Katakana (syllabograms). We studied 18 right-handed Japanese females, healthy, informed volunteers. Subjects observed a sequence of Kanji and Katakana words, both consisting of two syllables for 50 ms in either the left visual field (LVF) or the right visual field (RVF) at intervals of 2000 ms, while 39-channel-EEG were recorded. Four average ERP map series were separately averaged using letter criterion and stimulus conditions for each subject. The ERPs from all conditions and subjects were averaged and segmented into microstates, which were quasi-stable landscapes of potential distribution maps. The microstate topographies were assessed numerically by the electric gravity center, a conservative estimate of the mean location of all intracerebral, active, electric sources. To assess the differences of the electric gravity center between Kanji and Katakana, the mean vector was compared between two conditions using a paired t-test. Significantly, different microstates were found between Kanji and Katakana. In the RVF presentation, Kanji were more right lateralized than Katakana at 178–262 ms, and in the LVF presentation, Kanji were also more right lateralized than Katakana at 214–338 ms. These temporal and spatial aspects suggest that the differences between Kanji and Katakana reading already appear at early information processing stages, and this difference was independent of the input hemisphere.