The categorization of thought disorder

We describe the development of a new system for categorizing thought disorder. In the development phase (Study 1), we examined the degree to which speech samples and definitions of thought disorder subtypes taken from: (1) the Scale for the Assessment of Thought, Language, and Communication (TLC); (2) the Thought Disorder Index (TDI); and (3) the Assessment of Bizarre-Idiosyncratic Thinking (BIT), reflected disturbances in form versus disturbances in content. Ratings were provided by naive judges, experienced clinicians, and linguistic experts. The results contributed to the development of a new system dividing thought disorder into disturbances in (1) fluency, (2) discourse coherence, (3) content, and (4) social convention. In the validation phase (Study 2), 21 schizophrenic and 19 manic subjects were interviewed, interpreted proverbs, and responded to Rorschach cards. Subjects' speech was rated using the TLC, TDI, and BIT. We also measured hallucinations, delusions, and digit span performance. The results of Study 2 provided evidence supporting the validity of our new categorization system.