Are anomalous perceptual experiences necessary for delusions?

Several theories of delusions suggest that anomalous perceptual experience is necessary for delusion formation. This study evaluated levels of anomalous perceptual experience in a large group of nonclinical participants from the general population (N = 337), a group of psychotic inpatients (N = 20), and 2 groups of hallucinating (N = 24) and nonhallucinating (N = 24) deluded patients. The aims of the study were to evaluate the hypothesis that pathological levels of anomalous perceptual experience were necessarily associated with delusions. Using the Cardiff Anomalous Perceptions Scale, the main finding was that as a group, nonhallucinating deluded patients were not significantly different from nonclinical participants on any of the anomalous perceptual experience indices. We conclude that anomalous perceptual experience, as measured by the Cardiff Anomalous Perceptions Scale, is not necessary for the presence of delusions.