Perception, mental imagery and reality discrimination in hallucinating andnon-hallucinating schizophrenic patients

Objectives. In this study the hypothesis was tested that hallucinations res ult from confusing external and internal stimulus sources, i.e., perception and imagery, respectively. Design and methods. Thirteen hallucinating and 19 non-hallucinating schizop hrenic patients, as well as 14 control participants performed multiple test s of perception, vividness of mental imagery and the ability to discriminat e between them (reality discrimination). These functions were tested in bot h the auditory and the visual modalities. Results. There were no group differences on perceptual acuity. The results on one imagery task indicated that for the hallucinating patients, the rela tive, but not the absolute, level of vividness of mental images might be hi gher in the auditory modality, which was the modality in which 12 of the pa tients also experienced hallucinations, than in the visual modality. Finall y, there was a positive relationship between severity of (auditory) halluci nations and reality discrimination problems. Conclusions. Hallucinations may result from increased vividness of mental i magery, and their severity increases with larger impairments in reality dis crimination. It is recommended that research into, and cognitive behavioura l therapy for, hallucinations should also focus on their sensory qualities.