(2) Spatiotemporal Human Brain Activities by Visual Stimulus of Directional Characters and Symbols
Takahiro YAMANOI, Hisashi TOYOSHIMA, Shin-ichi OHNISHI, Toshimasa YAMAZAKI and Michio SUGENO
3rd International Symposium on Computational Intelligence and Intelligent Informatics. ISCIII 2007, pp.195-198，2007-3
To investigate the brain activity during human recognition of characters and symbols with directional meanings, the authors recorded electroencephalograms (EEGs) from subjects in viewing four types of Kanji (Chinese characters being used currently in the Japanese language) and four arrows presented on the CRT which means direction for Upward, Downward, Leftward and Rightward. As a result, the reaction time for each direction was almost equal, when characters or arrows were presented, regardless of the directions. However, for all the directions, the latency of peak for character was longer than that for arrow. The latency of peak for the word meaning upward or downward was a little shorter than those for other characters. EEGs were averaged for each stimulus type, and event-related potentials (ERPs) were determined. Tendencies in ERPs were compared, and marked changes in amplitude were seen near a latency of 420 ms for "上" (upward) and "下" (downward) and 500 ms for "左" (leftward) and "右" (rightward). Marked changes in amplitude were seen near a latency of 500 ms for all arrow symbols. When comparing ERPs between kanji characters and arrow symbols, differences in latency were noted, as were similarities in marked amplitude changes. When comparing ERPs between kanji characters and arrow symbols with opposing meanings, peak latencies for marked amplitude changes were predominantly similar, but polarities were opposite. Peak latency of ERPs was subjected to equivalent current dipole source localization (ECDL). ECD was estimated at a latency of around 110 ms in the MT field and then around 300 ms in the precentral gyrus. No marked differences in this tendency were noted among the eight stimuli. After ECD was estimated in the precentral gyrus, with the kanji characters, ECD was estimated in the right middle temporal gyrus regardless of direction. ECD was then estimated in areas related to language, such as the Wernicke's area in the left middle temporal gyrus, the left angular gyrus and the left lingual gyrus. ECD was later estimated in the left middle frontal gyrus, left inferior frontal gyrus and prefrontal area. ECD was estimated in the precentral gyrus just before the amplitude of ERPs changed markedly. With arrow symbols, ECD was estimated in the right middle temporal gyrus, and then ECD was estimated in areas related to working memory for spatial perception, such as the right inferior or right middle frontal gyrus. Then, as with kanji characters, ECD was estimated in the prefrontal area and precentral gyrus.
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