Repetition is good? An Internet trial on the illusory truth effect in schizophrenia and nonclinical participants

Abstract

Background and objectivesThe investigation of cognitive biases has considerably broadened our understanding of the cognitive underpinnings of schizophrenia. This is the first study to investigate the illusory truth or validity effect in schizophrenia, which denotes the phenomenon that the renewed exposure to difficult knowledge questions shifts responses toward affirmation. We hypothesized an excess of the truth effect in schizophrenia, which may play a role in the maintenance of the disorder, particularly relating to positive symptoms. MethodsThe study was set up over the Internet. The final analyses considered 36 patients with a probable diagnosis of schizophrenia, and a sample of 40 healthy subjects. Both groups took part on two occasions. In the baseline survey, difficult knowledge questions on neutral (e.g., “On each continent there is a town called Rome.” (true)) or emotional (delusion-relevant; e.g., “The German federal police uses approximately 3000 cameras for the purpose of video-based face-detection.” (not true)) topics were presented as statements, which were either correct or incorrect. After one week, subjects were requested to take part in the second and final survey. Here, previously presented as well as novel statements had to be appraised according to their truth. ResultsAs expected, an overall truth effect was found: statements that were repeated achieved higher subjective truth ratings than novel statements. Patients high on positive symptoms showed an excessive truth effect for emotional (delusion-relevant) items. The positive syndrome was correlated with the emotional truth effect in both healthy and schizophrenia participants. LimitationsThe sample was recruited via online forums and had probable but not externally validated diagnoses of schizophrenia. No psychiatric control group was tested. DiscussionThe truth effect for emotional items appears to be exaggerated in patients high on positive symptoms, which may play a role in delusion formation and maintenance. Several limitations of the study however render our conclusions preliminary. As patients with schizophrenia often dwell on and ruminate over selective and distorted pieces of information (e.g., conspiracy theories), the subjective authenticity of this information may be further elevated by means of the truth effect.