A condition in which reading (reading and understanding the meaning of written letters and sentences) is impaired, even though vision is normal and speech is unimpaired. Also called dyslexia or visual aphasia. Writing is usually normal, but reading aloud is often impaired. It is generally believed that alexia occurs when the left angular gyrus of the cerebrum is damaged later in life. Aphasic alexia, which is a partial symptom of aphasia, or alexia and agraphia, in which reading and spontaneous writing are impaired due to destruction of the written language center in the left parietal lobe, are often seen, but pure alexia is also rarely seen. Aphasic alexia involves simultaneous impairments in reading aloud and reading and comprehension, but in some cases impairment in only one of these is particularly pronounced. There are also cases where impairments differ between reading kana and reading kanji, and cases where a patient can understand characters but not sentences. In contrast, pure alexia is also called visual agnosia alexia, in which the patient is able to speak, hear, and write almost normally, but visual agnosia, in which only reading is impaired, is prominent. Incidentally, impairments in reading that result in misreading are called paradoxes. [Editorial Department] [Reference] |Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
視覚が正常で発語にも支障がないのに、読字(書かれた文字や文章を読んで意味を理解すること)だけが障害された状態。読字不能あるいは視覚性失語症ともいう。書字は正常であることがほとんどであるが、音読の障害が多く認められる。一般に大脳の左角回(かくかい)が後天的に障害されると失読症を起こすとされている。失語性失読とよばれる、失語症の部分症状としての失読、あるいは左頭頂葉の書字言語中枢の破壊により読字と自発書字が障害される失読失書がみられることが多いが、純粋失読もまれにみられる。 失語性失読では音読と読字・読解の障害を同時に伴うが、その一方だけの障害がとくに顕著な場合もある。また、かなと漢字の読みで障害に違いが認められる場合や、文字は理解できても文章は理解できない場合もある。これに対して、純粋失読は視覚失認性失読ともよばれるように、話したり聞いたり文字を書いたりすることはほとんど普通にできるが、読字だけが障害される視覚性失認が顕著に認められる。なお、読字が障害されて読み違いが生じることは錯読という。 [編集部] [参照項目] |出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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