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＜Doctoral Thesis＞
Differential roles of spatial frequency on reading processes for ideograms and phonograms : A high-density ERP study
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| Abstract | 日本の表意文字(漢字)と表音文字(仮名)の神経基盤の乖離は、今のところ明らかでない。本研究では、空間周波数(SF)情報が漢字と仮名の脳内処理の違いに関与しているかを調べるため、日本語を母国語とする被験者が未フィルター処理あるいは空間フィルター処理した文字刺激を読んでいる時の脳活動を、高密度事象関連電位(ERP)を用いて測定した。刺激には、漢字(低学年で学習する漢字･高学年で学習する漢字)、仮名(仮...名語･非語)とスクランブル文字を用いた。フーリエ解析では、漢字は高空間周波数(HSF)、仮名は低空間周波数(LSF)にそれぞれ特徴づけられた。未フィルター処理刺激では、両側後頭部にP100、左後側頭部にN170、前頭～中央部にN400のERP成分が誘発された。スクランブル文字では、N170は左優位性を示さず、N400は明瞭には誘発されなかった。LSF条件では、漢字のP100とN170の潜時が、仮名より有意に延長した。HSF条件では、高学年で学習する漢字のP100とN170の潜時が、低学年で学習する漢字より有意に延長した。HSF･LSF条件とも、N400では漢字と仮名の差は認めなかった。以上の結果、SFが意味的成分ではなく早期の視覚反応に影響することで、漢字と仮名の処理の差が生じることが示唆される。つまり、仮名とLSF情報、漢字とHSF情報はそれぞれ密接な連関があり、漢字･仮名の読みの神経基盤の乖離には、SF情報の違いが関与している。 The neural substrate of the dissociation between reading Japanese ideograms (Kanji) and phonograms (Kana) is currently unclear. To test whether spatial frequency (SF) information is responsible for this phenomenon, we recorded high-density event-related potentials (ERPs) with unfiltered or spatially filtered word stimuli in Japanese-speaking subjects. Kanji (early-learned, late-learned), Kana (word, non-word), and scrambled characters served as stimuli. Fourier analysis revealed that Kanji and Kana were characterized by high-SF (HSF) and low-SF (LSF) information, respectively. In ERPs with unfiltered stimuli, bilateral occipital P100, left occipitotemporal N170 and fronto-central N400 were elicited. Scrambled characters did not evoke left-lateralized N170 or clear N400. Under the LSF condition, P100 and N170 latencies for Kanji were significantly longer than for Kana. In the HSF condition, P100 and N170 latencies for late-learned Kanji were significantly longer than for early-learned Kanji. There was no significant difference in the N400 between Kanji and Kana in both SF conditions. These results suggest that early visual responses, but not the semantic component, are influenced by SF. This indicates a close link between Kana and LSF information, and between Kanji and HSF information. The differential effects of SF could underlie the neural basis of the differences between Kanji and Kana reading.show more |
| Table of Contents | 1. Introduction 2. Materials and Methods 3. Results 4. Discussion Acknowledgments References |
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| Created Date | 2013.07.12 |
| Modified Date | 2023.12.08 |