Source monitoring and olfactory hallucinations in schizophrenia

People with schizophrenia who experience auditory-verbal hallucinations experience difficulty in determiningthe source (self vs. other) of verbal information, and those with visual hallucinations experiencea conceptually similar problem with visual information. In this study, we examined whether such sourcemonitoring deficits extend to olfaction for olfactory hallucinators and whether they are selective to themodality in which the hallucination is experienced. To test these claims, three groups were formed:normal controls (NC), people with schizophrenia who experience olfactory hallucinations (OH), andpeople with schizophrenia who experience auditory-verbal hallucinations (AVH). These three groupswere then tested on both an olfactory and an auditory-verbal source-monitoring task. We found evidenceof a modality-specific impairment. The OH group was less accurate in determining whether an odor hadbeen imagined or smelled relative to NC and AVH groups. In contrast, the AVH group was least accuratein determining the source of a word, relative to the OH and NC groups. These findings provide the firstevidence of a source-monitoring impairment in schizophrenic participants with OHs and suggest that thisimpairment is modality specific.