Impaired discrimination between imagined and performed actions in schizophrenia.

The main aim of the present study was to investigate whether a specific type of source monitoring, namely self-monitoring for actions (differentiation between imagined and performed actions), is disrupted in schizophrenia. Persons diagnosed with schizophrenia (n=32) and healthy participants (n=32) were assessed with an action memory task. Simple actions were presented to the participants either verbally (short instructions) or nonverbally (icons). Some of the items required participants to physically perform the action whereas other actions had to be imagined. In the recognition phase of the study, participants were asked whether an action was previously displayed (verbally or nonverbally), whether it was a new action (not presented before), and if they had performed or imagined the action. In addition, participants were asked how confident they were in their decision. Participants in the group with schizophrenia significantly more often misattributed imagined actions as performed and vice versa and were more convinced about their wrong decision than participants in the control group. Patients revealed worse recognition for both verbal and nonverbal actions. In accordance with prior studies, we found that patients were less confident in their correct answers than healthy subjects. However, no enhanced confidence in incorrect answers was found. There was no observed significant relationship between source misattributions and the severity of psychopathological symptoms. Our findings suggest tentatively general source monitoring deficits in schizophrenia.