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A cognitive neuropsychological approach to the study of delusions in late-onset schizophrenia
M L Phillips1, R Howard, A S David
1Department of Psychological Medicine, Kings College Hospital, London, UK.
Objective:
Hypotheses to explain delusion formation include distorted perceptual processing of meaningful stimuli (e.g. faces), abnormal reasoning, or a combination of both. The study investigated these hypotheses using standardized neuropsychological tests.
Design:
A three-patient case-study, compared with a small group (n = 8) of age-matched normal control subjects.
Setting:
Hospital in- and outpatients. Age-matched normal controls were from local residential homes.
Patients:
Three subjects with late-onset schizophrenia, two currently deluded and one in remission. Both deluded subjects had persecutory beliefs. One had a delusion of misidentification.
Interventions:
All subjects were administered standardized neuropsychological tests of facial processing and tests of verbal reasoning.
Main Outcome Measures:
The test scores of the three patients were compared with published normal values and the age-matched control data.
Results:
The tests demonstrated impaired matching of unfamiliar faces in deluded subjects, particularly in the subject with delusional misidentification. Increasing the emotional content of logical reasoning problems had a significant effect on the deluded subjects' reasoning but not that of the normal controls.
Conclusion:
The findings suggest impaired visual processing plus abnormal reasoning in deluded subjects. However, these impairments are relatively subtle given the severity of psychiatric disorder in the patients studied.