Testing continuum models of psychosis: No reduction in source monitoring ability in healthy individuals prone to auditory hallucinations

Abstract

People with schizophrenia who hallucinate show impairments in reality monitoring (the ability to distinguish internally generated information from information obtained from external sources) compared to non-hallucinating patients and healthy individuals. While this may be explained at least in part by an increased externalizing bias, it remains unclear whether this impairment is specific to reality monitoring, or whether it also reflects a general deficit in the monitoring of self-generated information (internal source monitoring). Much interest has focused recently on continuum models of psychosis which argue that hallucination-proneness is distributed in clinical and non-clinical groups, but few studies have directly investigated reality monitoring and internal source monitoring abilities in healthy individuals with a proneness to hallucinations. Two experiments are presented here: the first (N = 47, with participants selected for hallucination-proneness from a larger sample of 677 adults) found no evidence of an impairment or externalizing bias on a reality monitoring task in hallucination-prone individuals; the second (N = 124) found no evidence of atypical performance on an internal source monitoring task in hallucination-prone individuals. The significance of these findings is reviewed in light of the clinical evidence and the implications for models of hallucination generation discussed.

Keywords: Auditory verbal hallucinations; Internal source monitoring; Reality monitoring; Schizophrenia.

Fig. 1

Stimuli used in the Reality Monitoring Tasks. Note: Sample stimuli used in the study phase (left) and test phase (right) of the reality monitoring task. In a 2 × 2 design, either the subject or experimenter spoke aloud the stimuli, which were presented either complete (perceived) or incomplete (requiring the second word to be imagined). Subjects were then presented at test with the first word of a word pair, and asked to judge whether the accompanying word had been seen or imagined, or if the presented word was new; or whether the subject or experimenter had read aloud the word pair, or the presented word was new.

Fig. 2

Misattribution errors. Note: The two charts refer to items misclassified for each of the reality monitoring tasks, broken down by the trial conditions. So for example, the first 2 bars in the left chart refer to items which had been imagined by the subject, which were then incorrectly judged as perceived (an externalisation error), and the last 2 bars in the right chart to items which had been imagined by the experimenter during encoding, but which the subject had later judged to have been self-imagined (an internalisation error).