Ichi, Ni, 3, 4: Neural representation of kana, kanji, and Arabic numbers in native Japanese speakers

The Japanese language represents numbers in kana digit words (a syllabic notation), kanji numbers and Arabic numbers (logographic notations). Kanji and Arabic numbers have previously shown similar patterns of numerical processing, and because of their shared logographic properties may exhibit similar brain areas of numerical representation. Kana digit words require a larger phonetic component, and therefore may show different areas of numerical representation as compared to kanji or Arabic numbers. The present study investigated behavioral reaction times and brain activation with fMRI during the numerical processing of kana digit words, kanji numbers and Arabic numbers. No differences in behavioral reaction time were found between kanji and Arabic numbers. In contrast, kana digit words produced a longer reaction time as compared to the other two notations. The imaging data showed that kana activated the posterior cingulate cortex when compared to kanji and Arabic numbers. It is suggested that this posterior cingulate activation reflects an additional attentional demand in this script which may be related to the infrequent use of kana digit words, or may reflect an extra step of phonological mediation in converting the visual word form to the verbal word form. Overall, the data suggest that number reading is processed differently in these three notations.