DISSOCIATIONS OF LANGUAGE FUNCTION IN DEMENTIA - CASE-STUDY

In this report we describe and attempt to characterize the deterioration in semantic knowledge occurring in a victim of a progressive dementing disease. The subject was unable to match even highly familiar naming words with their actual or pictured referents; instead, she consistently overextended verbal labels to closely associated distractors. The alteration in scope of referential meanings suggested by this overextension effect was apparently related to a breakdown in the structure of underlying categories. On a nonverbal match-to-sample procedure, for example, dogs were treated as exemplars of the cat family. Evidence for the breakdown of semantic knowledge was not limited to picture labeling paradigms. Thus, we found that the subject was unable to utilize semantic context in the written disambiguation of spoken homophones but could, at the same time, use even minimal syntactic cues as the basis for proper lexical selection. This last result was consistent with other lines of evidence pointing to the relative preservation of syntactic operations, in marked contrast to the semantic loss. The importance of this dissociation of function in organic pathology is considered from a number of perspectives, including its relevance to models of language organization in the brain. © 1979.