Background. In order to elucidate further the cognitive processes underlying auditory hallucinations, an experiment investigating delayed and immediate source monitoring for positive, negative and neutral verbal material was conducted with schizophrenic patients.

Methods. Patients experiencing auditory hallucinations, patients not experiencing auditory hallucinations and normal subjects participated in a word association task, rating their responses for how much a self-generated thought was their own, how controllable and involuntary it was and their confidence in these ratings. A delayed source monitoring test in which subjects had to recall the source (self or experimenter) of the words from the association task was also administered.

Results. Hallucinators showed a greater bias towards external attribution of their thoughts compared with both control groups for immediate attributions of source, but not for delayed attributions. Hallucinators showed a bias towards external attribution of emotional material for immediate source monitoring and all subjects showed a bias towards misattribution of positive material to an external source and negative material to an internal source for the delayed source monitoring task.

Conclusions. These findings appear to be most consistent with theories proposing that hallucinations result from an external attributional bias for internal events. The implications of these results for research and practice are also discussed.