意味処理障害からみる脳内の意味表象

Abstract

基本レベルカテゴリーの語彙の意味処理が主に障害されると、モノの名称を答える呼称課題において、名称のみで答えることができず過度に具体的に表現してしまうという特徴的な症状がみられ、これは抽象的態度の障害 (Goldstein1948) と呼ばれる。本稿では抽象的態度の障害を呈した症例の症状をプロトタイプ理論の枠組みを用いて分析し、基本レベルカテゴリーの語彙の名称と結びつく意味は、本来はプロトタイプの成員に近い視覚的イメージとして脳内で表象されており、それが障害された結果、抽象化を経る前の対象の知覚情報、もしくは基本レベルより抽象度の高い上位レベルの意味表象が、当該語彙の名称と相対的に強い記号関係を有するようになるということを示す。また、抽象度の違いにより意味表象の神経基盤が異なるという可能性について言及する。

Aphasia is an impairment of intellectual language, which is achieved by the activation of semantic representations prior to the selection of associated phonological forms. This paper examines the impairment of abstract attitudes reported by Goldstein (1948), which is caused by an impairment of the semantic categorization system in aphasia, from the perspective of prototype theory in cognitive linguistics. By analyzing the responses to naming tasks performed on a patient with an impairment of abstract attitude, the author shows that the phonological forms of words in the basic category are associated with visual representations similar to their prototypical instances in semantic memory. Patients with an impairment of abstract attitude have weaker associations between phonological forms and these visual representations of basiclevel category words than do unimpaired people. Instead, the phonological forms are associated more with semantic knowledge of the higher category and perceptual information in episodic memory than with the visual representations in semantic memory. This leads not only to word finding difficulties, but also to a variety of symptoms such as difficulties with the visual top-down process in picture naming tasks, semantic paraphasia, and overly concrete expressions.