Cognitive substrates of thought disorder, I: The semantic system

Objective: Few studies have explored in detail the relation of cognitive de ficits in attention, working memory, and semantics to thought disorder. The authors sought to determine whether thought disorder resides in the semant ic system or elsewhere. Method: Twenty-three normal comparison subjects and 23 patients with schizophrenia participated in the study. Ail subjects rec eived tests of executive function and working memory, including the Wiscons in Card Sorting Test and the Letter-Number Span test; a test of deployment of attentional resources; and tests of semantic processing and language com prehension, including the Peabody Picture Vocabulary Test, the Speed and Ca pacity of Language-Processing Test, the Boston Naming Test, and tests of se mantic verbal fluency and phonologic verbal fluency, from which was derived a difference score. All patients were also administered the Scale for the Assessment of Thought, Language, and Communication to assess thought disord er. Results: The normal subjects were compared with the schizophrenic patie nts who were rated as having mild thought disorder (N=13) or moderate to se vere thought disorder (N=10). While differences between the schizophrenic s ubgroups and the comparison subjects were observed on nearly all tests, a l arge difference in effect size between the two schizophrenic subgroups was apparent only in the verbal fluency difference score. in a series of multip le regression analyses, two variables made significant contributions to the prediction of positive thought disorder: the verbal fluency difference sco re and the Peabody Picture Vocabulary Test score. Conclusions: These result s suggest that clinically rated thought disorder is associated with and may result from semantic processing abnormalities. In particular, patients wit h more severe thought disorder may have difficulty accessing semantic items because of disorganization of the semantic systems and, to a more limited degree, may also lack a semantic or conceptual knowledge base.