Delusions in schizophrenia: a phenomenological and psychological exploration.

The psychopathological basis of delusions in schizophrenia is poorly understood. The most enduring of several early theories has suggested a causal link with formal thought disorder, whereas recent approaches have proposed relationships with a variety of cognitive abnormalities. The correlations of delusions with other schizophrenic symptoms and with cognitive functions including semantic memory, executive function, and also probabilistic reasoning bias, were examined in a series of (overlapping) groups of 43-79 schizophrenic patients. Delusions were found to be significantly correlated with formal thought disorder, with evidence for a particular link between bizarreness and fragmentariness of delusions and "loosening of association". Delusions were not significantly correlated with overall intellectual function or memory, although there was some suggestion of a complex interaction between delusions, formal thought disorder, and semantic memory impairment. No association between delusions, formal thought disorder, and any measure of executive function was found. Although, as a group, schizophrenic patients showed evidence of probabilistic reasoning bias, this was unrelated to presence and severity of delusions.