Positive symptomatology and source-monitoring failure in schizophrenia--an analysis of symptom-specific effects

Recent research has suggested that certain positive symptoms in patients with schizophrenia are linked to self monitoring/reality-monitoring deficits. We wished to investigate the association between such deficits and three specific symptoms: hallucinations, delusions and thought disorganisation. Forty patients with schizophrenia and 40 normal controls were administered a source-monitoring task. Twenty-four items were produced, either verbally by the experimenter, or verbally by the subject, or presented as pictures. Then, subjects were read a recognition list including the produced target items mixed with distractors. They were required to recognise the target items and to remember their source of production. The pattern of memory deficits has previously been reported (Brébion, G., Smith, M., Gorman, J., Amador, X., 1997. Discrimination accuracy and decision biases in different types of reality monitoring in schizophrenia. Journal of Nervous and Mental Disease 185, 247-253). The current analyses focussed on the false recognition of distractors, and on the errors in the source attribution of the recognised target items. Results showed that higher hallucination scores were associated with an increased tendency towards false recognition of non-produced items. In addition, hallucinators were more prone than control subjects to misattribute to another source the items they had produced themselves. Furthermore, hallucinators and delusional patients were more prone than the other patients to report that spoken items had been presented as pictures. This latter finding suggests that both hallucinations and delusions are associated with confusion between imagined and perceived pictures. Our previous report stated that only one of the three investigated types of response bias was associated with global positive symptomatology. However, this finer-grained analysis revealed that the three of them were in fact associated with hallucinations and/or delusions. On the other hand, thought disorganisation appeared to be independent from these mechanisms.