Externalizing biases and hallucinations in source-monitoring, self-monitoring and signal detection studies: a meta-analytic review

Background. Cognitive models have postulated that auditory hallucinations arise from the misattribution of internally generated cognitive events to external sources. Several experimental paradigms have been developed to assess this externalizing bias in clinical and non-clinical hallucination-prone samples, including source-monitoring, verbal self-monitoring and auditory signal detection tasks. This meta-analysis aims to synthesize the wealth of empirical findings from these experimental studies. Method. A database search was carried out for reports between January 1985 and March 2012. Additional studies were retrieved by contacting authors and screening references of eligible reports. Studies were considered eligible if they compared either (i) hallucinating and non-hallucinating patients with comparable diagnoses, or (ii) non-clinical hallucination-prone and non-prone participants using source-monitoring, verbal self-monitoring or signal detection tasks, or used correlational analyses to estimate comparable effects. Results. The analysis included 15 clinical (240 hallucinating patients and 249 non-hallucinating patients) and nine non-clinical studies (171 hallucination-prone and 177 non-prone participants; 57 participants in a correlation study). Moderate-to-large summary effects were observed in both the clinical and analogue samples. Robust and significant effects were observed in source-monitoring and signal detection studies, but not in self-monitoring studies, possibly due to the small numbers of eligible studies in this subgroup. The use of emotionally valenced stimuli led to effects of similar magnitude to the use of neutral stimuli. Conclusions. The findings suggest that externalizing biases are important cognitive underpinnings of hallucinatory experiences. Clinical interventions targeting these biases should be explored as possible treatments for clients with distressing voices.