Normal and impaired reading of Japanese kanji and kana

Two kinds of scripts are used in the written forms of Japanese words: morphographic kanji and phonographic kana. Whereas each kana character invariably represents a single pronunciation, the majority of kanji characters have two or more legitimate pronunciations, with one appropriate to the character in any given word. Furthermore, each kanji character has meaning while a kana character does not. On the basis of these and other differences between kanji and kana, some traditional views assume that, in reading aloud, kanji is processed by a semantic/lexical system while kana is processed by a phonological/rule system. We review accumulating evidence from our research that argues against these traditional views. (1) In reading aloud twocharacter kanji words, normal readers are slower on lowfrequency words with statistically atypical character-sound correspondences than either high-frequency words or words with statistically typical correspondences. (2) Normal readers are easily capable of reading aloud two-character kanji nonwords. (3) Normal readers are slower on low-imageability words than high-imageability words, but the imageability effect emerges only for low-familiarity kanji words with atypical character-sound correspondences. (4) Although Japanese surface dyslexia has been described as a selective reading disorder on kanji words, recently reported cases reveal good kanji performance for high-frequency words and words with statistically typical correspondences, despite a profound deficit on low-frequency words with atypical character-sound correspondences. (5) In reading aloud kana nonwords, normal readers are faster on pseudohomophones (orthographic nonwords with a familiar phonological pattern, created by transcribing kanji words into kana strings) than nonwords not homophonic with any words, but this significant advantage emerges only when the pseudohomophones share their pronunciations with high-imageability words. (6) Although Japanese phonological dyslexia has been considered a selective reading disorder on kana nonwords, a recently reported case showed good performance on pseudohomophones with the identical pronunciation to high-familiarity and high-imageability words, despite a profound deficit on nonhomophonic nonwords. These data suggest that phonology of both kanji and kana strings is computed directly from orthography, with additional reliance on semantics when the direct computation is inefficient. 1. JAPANESE ORTHOGRAPHY The spoken form of a Japanese word comprises a sequence of from one to several morae (e.g., /ni-ho-N/ "Japan"). A mora corresponds to a single vowel (V), a consonant-vowel compound (CV), a palatalized consonant-vowel compound (CjV), the nasal coda (N) which can follow a V, CV, or CjV mora, or a geminate consonant (Q: its acoustic entity is, for example, a prolonged silent period before the following plosive consonant). Two kinds of scripts are used in the written forms of Japanese words: morphographic kanji and phonographic kana. Kanji comprises approximately 6,000 characters, with about half of these used in daily life. Some kanji characters appear as a single-character noun (空 /sora/ "sky"), as a component of multiple-character kanji nouns (空気 /kuu-ki/ "air", 空色 /sorairo/ "sky blue", 空手 /kara-te/ "Japanese traditional fight"), and as the stems of kanji-kana compound verbs (空く /a-ku/ "become vacant") and adjectives (空しい /muna-si-i/ "fruitless"). Other characters appear only in one, two, or three of these written word classes. A kanji character does not reliably map to any specific size of phonological unit like a phoneme, a mora, a syllable, or a word, and cannot be decomposed into elements which correspond to phonemes or morae. The majority of kanji characters have two or more legitimate pronunciations, which generally contain from one to three morae, with the one pronunciation appropriate for the character in any given word determined by intraword context. The pronunciations of a kanji character can be divided into ON and KUN. When kanji characters were imported from China, their pronunciations also entered the Japanese spoken language; an ON pronunciation (or ON-reading) derives from the pronunciation of an original Chinese character (e.g., /kuu/ for 空 in 空気 /kuu-ki/). A KUN pronunciation (or KUN-reading), on the other hand, derives from the pronunciation of an original spoken Japanese word which has the same meaning as the Chinese character (e.g., /sora/ for 空). Because Chinese and Japanese are completely different spoken languages, there is usually no phonological similarity between the ON and KUN pronunciations of any given kanji character. Furthermore, a kanji character represents not only its phonology but also its semantic domain. For example, a meaning related to "sky", "empty", or "vacant" seems to be shared across the words including 空 even if the pronunciations for 空 vary across the words. Kana is sub-divided into hiragana (cursive form) and katakana (square form). Hiragana is used for most function words (そし て /so-si-te/ "and"), some content words (りんご /ri-N-go/ "apple"), and the inflections of verbs (空く /a-ku/ "become vacant") and adjectives (空しい /muna-si-i/ "fruitless"), whereas katakana is used for loan words (テスト /te-su-to/ "test") from western languages. Both hiragana and katakana comprise 75 characters, and there is always a pair of hiragana and katakana characters representing the same pronunciation. A kana character usually maps to a single mora of spoken Japanese: Five characters correspond to a single vowel (e.g.,あ /a/), 65 correspond to a consonant-vowel compound (e.g., き /ki/, や /ja/), one corresponds to a nasal coda (ん /N/), and one corresponds to gemination (っ /Q/). Although three kana characters do not ! " ISCA Archive