Background:
One of the primary cognitive abnormalities in schizophrenia is a semantic memory deficit, which is predicted to underpin disturbances in language processing. Similarly, memory deficits have been acknowledged as a consequence of mood extremes, such as in depression and bipolar disorder. The precise impact of semantic memory deficits on word comprehension, particularly in terms of processing across grammatical categories, has not been adequately investigated. Furthermore, previous semantic assessments have predominantly been designed in a way that most healthy controls perform at ceiling, questioning the accuracy of observed differences between patient and control groups.
Methods:
A new word definition task was designed to overcome the ceiling effect. It was developed for elucidating semantic disorganization in word comprehension across grammatical categories (ie nouns, verbs and adjectives) and administered to 32 patients with schizophrenia, 28 patients with bipolar disorder and 32 matched healthy controls.
Results:
A 3 × 2 × 3 × 2 repeated-measures ANOVA indicated that while both patient groups illustrated semantic processing deficits when compared with healthy controls, word comprehension across grammatical categories was comparable despite diagnosis, as was the influence of word frequency. All subject groups were better at defining adjectives compared with nouns and verbs, and comprehension increased for high-frequency words.
Conclusions:
Despite the semantic processing deficits illustrated by both patient groups, processing of grammatical categories was not differentiated by the presence of psychosis. Additional research into the role of encoding, word organization, and specific basis for variation in the processing of adjectives warrants further research.
