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

BACKGROUND AND OBJECTIVES: The 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. METHODS: The 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. RESULTS: As 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. LIMITATIONS: The sample was recruited via online forums and had probable but not externally validated diagnoses of schizophrenia. No psychiatric control group was tested. DISCUSSION: The 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.

The truth about the truth: a meta-analytic review of the truth effect.

Repetition has been shown to increase subjective truth ratings of trivia statements. This truth effect can be measured in two ways: (a) as the increase in subjective truth from the first to the second encounter (within-items criterion) and (b) as the difference in truth ratings between repeated and other new statements (between-items criterion). Qualitative differences are assumed between the processes underlying both criteria. A meta-analysis of the truth effect was conducted that compared the two criteria. In all, 51 studies of the repetition-induced truth effect were included in the analysis. Results indicate that the between-items effect is larger than the within-items effect. Moderator analyses reveal that several moderators affect both effects differentially. This lends support to the notion that different psychological comparison processes may underlie the two effects. The results are discussed within the processing fluency account of the truth effect.