Discrimination accuracy and decision biases in different types of reality monitoring in schizophrenia.

A reality monitoring task was administered to 31 schizophrenic patients and 31 normal controls. Twenty-four items were produced, either orally by the experimenter, orally by the subjects, or seen as pictures. Subjects were later read a list of 48 items and were asked to indicate if each item was new, self-generated, experimenter-generated, or presented as a picture. Results showed that schizophrenic patients were impaired in discriminating old items from new, with a higher bias than controls toward reporting new items as if they were old (false alarms). In addition, patients were impaired in discriminating self-generated items from externally generated items, with a higher bias than controls toward attributing self-generated items to an external source. Lastly, they were significantly impaired in discriminating the modality (auditory versus visual) in which the event was presented. The bias toward remembering orally produced items as pictures was correlated with positive symptomatology and was significantly higher than controls in patients with high levels of positive symptoms. This suggests that mental imagery may play a role in positive symptomatology. These results demonstrate the relevance of studying decision biases along with discrimination performance for the understanding of the mechanisms of reality monitoring impairment in schizophrenia.