Source monitoring biases and auditory hallucinations

Abstract

Introduction. Previous source monitoring studies on schizophrenia reported an association between external source misattribution and hallucinations, but this is often not replicated. This inconsistency may be attributable to a failure in accounting for guessing parameters when computing source monitoring biases.

Methods. Fifty-one patients and 20 healthy controls were required to recall the source of items originating from external (computer and experimenter) or internal (the subject) sources. When statistically determined criteria were met, the appropriate counts of false positives were entered as covariates in the statistical analyses (analysis of covariance; ANCOVA) to exclude guessing from source monitoring bias measures.

Results. When comparing patients to controls, impairments on item recognition and source discrimination were observed. When comparing patient groups split on hallucinations, a bias towards attributing self-generated items to an external source was observed. A group difference on the externalisation bias was absent when the sample was split on delusions.

Conclusions. A bias towards attributing self-generated items to an external source was associated with hallucinations. This ANCOVA methodology is recommended for source monitoring studies investigating group differences, and suggests that previously reported null results may be attributable to a failure in separating guessing and source monitoring measures.

Acknowledgements

Mahesh Menon is now exclusively affiliated with the Schizophrenia PET Group, Centre for Addiction & Mental Health, Toronto, Canada. Jennifer C. Whitman is now affiliated exclusively with the Department of Psychology, Simon Fraser University, Burnaby, British Columbia, Canada. We thank Carrie Cuttler and Tonya Kragelj for assistance with stimulus preparation, data collection, and data management. This research was supported by grants from the Canadian Psychiatric Research Foundation, the Canadian Institutes for Health Research, the Riverview Hospital Academic Steering Committee and the Mind Foundation of BC to TSW, and a Parke-Davis Fellowship to MM.