Delusional thinking and cognitive disorder.

A hypothesis is presented regarding the genesis of paranoid delusion that attempts to take into account certain data. The data of interest are (a) the failure to find evidence of cognitive impairment in diagnosed paranoid patients, (b) the evidence of perceptual disorder as a primary and prior condition in the natural history of the clinical development of delusions and the empirical relationship of the perceptual disorder to presence of "thought disorder," (c) the failure to find evidence supporting universal psychodynamic patterns of etiology, (d) appearance of "delusional" phenomena in normal subjects in situations of deviant sensory experience, and (e) the reports of articulate patients writing of their experiences. This hypothesis suggests that there exists a group of patients who suffer from primary perceptual anomalies, fundamentally biological in nature although probably fluctuating with current stresses, and that these anomalies involve vivid and intense sensory input. These experiences demand explanation which the patient develops through the same cognitive mechanisms that are found in normal and scientific theory-building. As the data that are available to the patient are crucially different from those available to an observer, the latter judges the explanation to be bizarre and pathological. Being unable to check the validity of the patient's descriptions of his sensory experience the assumption is made that the patient is having the same experience as the observer but is defective in reality-testing and/or inferential thinking. As the evidence for the presence of perceptual disorder is stronger than the direct evidence for cognitive impairment, the hypothesis outlined here places central importance on the former. In brief, it is suggested that for many paranoid patients the delusion should be seen as the reaction of a normal, "sane" individual to abnormal but genuine perceptual experiences.