Theory of mind and the role of IQ in chronic disorganized schizophrenia.

Background: Several studies have suggested a theory of mind (ToM) deficit in schizophrenic disorders. However, the role of interfering variables such as IQ, attention, memory, and severity of the disorder has remained ambiguous.
Methods: A theory of mind picture story comprising a sequencing task, a first and a second order false belief test, and a tactical deception test was given to a group of 23 patients with chronic disorganized schizophrenia and to 12 healthy control persons. In addition, a nonsocial picture story had to be sequenced. Severity of the psychopathology was measured by using the brief psychiatric rating scale (BPRS), IQ was estimated using the 'Mehrfachwahlwortschatztest' (MWT, multiple choice verbal comprehension test).
Results: The schizophrenic group was impaired relative to controls on the theory of mind task, but not on the sequencing task of the nonsocial picture story. However, when controlled for IQ, no such difference was found. These findings were neither related to severity, duration, nor age at onset of the disorder.
Conclusions: Theory of mind deficits in schizophrenia may be related to domain general impairments, e.g., intelligence and working memory load, rather than reflecting a 'genuine' compromised mental state attribution similar to autistic spectrum disorders. Schizophrenic patients may, however, rather be impaired in how and when to apply strategic social reasoning. Further studies to investigate the nature of social deficiency in schizophrenia are warranted.