Thought disorder, pragmatic language impairment, and generalized cognitive decline in schizophrenia.

BACKGROUND Schizophrenia is associated with pragmatic language impairment (PLI), a reduced ability to communicate intention in a rule-governed fashion. Two explanations for PLI include that PLI is equivalent to thought disorder and that PLI is secondary to generalized cognitive decline. OBJECTIVES The aims of this study were to demonstrate PLI in schizophrenia and to test which of these explanations best accounts for the relationships among thought disorder, PLI, and generalized cognitive decline. METHOD Schizophrenia (n=20) and control (n=26) participants provided speech samples that were scored for thought disorder (type-token ratio and Cloze procedure) and PLI [Profile of Pragmatic Impairment in Communication (PPIC)]. Generalized cognitive decline was determined from discrepancies between current and premorbid verbal IQ. RESULTS Patients with schizophrenia exhibited significant PLI and generalized cognitive decline. There was no evidence of an association between thought disorder and PLI. Moreover, generalized cognitive decline predicted PLI (r(2)=0.33 to 0.59) but not thought disorder (r(2)=0.02 to 0.06). CONCLUSIONS The results conformed to a predicted pattern of associations based on the notion that PLI in schizophrenia is secondary to generalized cognitive decline.