To investigate how the human brain processes words and symbols with the same meanings, the following four words (Kanji: Chinese characters using in Japanese language) and four symbols (arrows) were utilized as visual stimuli: four words for upward, downward, leftward and rightward (??, ??, ?? and ??, respectively) and four arrow symbols for upward, downward, leftward and rightward (↑, ↓, ← and →, respectively). Electroencephalography (EEG) was performed while subjects were observing these visual stimuli. In each experiment, each visual stimulus was presented 30 times, for a total of 240 presentations of the eight visual stimuli. Subjects comprised four women aged from 20 to 21.
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 ?? (up) and ?? (down) and 500 ms for ?? (left) and ?? (right). 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 8 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 field 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, 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.
When comparing visual stimuli with opposite meanings, ECD was estimated in almost the same area at latencies where ERPs exhibited opposite peaks, but moments differed.
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