Disturbances of Word Meanings

Most recent research on disturbances of word meanings in brain-damaged patients has focused on words that refer to objects. Disturbances of word meanings cause poor performance on word-picture matching and naming tasks. However, the combination of deficits in word-picture matching and naming may be due to separate input- and output-side processing disturbances that affect word recognition and production. Cooccurring deficits in naming and word-picture matching are more likely to result from a disturbance affecting concepts when (i) the patient makes many semantic errors in providing words to pictures and definitions, (ii) he or she has trouble with word-picture matching with semantic but not phonological foils, (iii) he or she fails on categorization tasks with pictures, and (iv) the same words are affected in production and comprehension tasks.

Disorders affecting processing of semantic representations for objects may be specific to certain types of inputs. Elizabeth Warrington first noted a discrepancy between comprehension of words and pictures in two dementing patients. Dan Bub and colleagues described a patient who showed very poor comprehension of written and spoken words but quite good comprehension of pictures. These impairments have been taken as reflections of disturbances of "verbal" and "visual" semantic systems, although others have disputed this conclusion.

Semantic disturbances may also be category specific. Several authors have reported a selective semantic impairment of concepts related to living things and foods compared to man-made objects. The opposite pattern has also been found. Selective preservation and disruption of abstract versus concrete concepts, and of nominal versus verbal concepts, have also been reported.

Disturbances may affect the unconscious activation of semantic meanings or their conscious use. There are patients who cannot match words to pictures or name objects but who are unconsciously influenced by a word's meaning. For instance, in a word/nonword decision task, they will respond faster to the word "doctor" when it follows "nurse" than when it follows "house," indicating they are able to appreciate the relations between words unconsciously, even when they cannot indicate understanding of word meaning in conscious, controlled tasks such as word-picture matching. Conversely, some patients who appear to understand words well have abnormalities in tasks that examine unconscious processing of the meanings of words.

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