Belief beyond logic: An investigation of the role of intuitive reasoning in delusion formation and maintenance

Author: Alycia Budd

Budd, Alycia, 2024 Belief beyond logic: An investigation of the role of intuitive reasoning in delusion formation and maintenance, Flinders University, College of Education, Psychology and Social Work

Terms of Use: This electronic version is (or will be) made publicly available by Flinders University in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. You may use this material for uses permitted under the Copyright Act 1968. If you are the owner of any included third party copyright material and/or you believe that any material has been made available without permission of the copyright owner please contact with the details.


Clinical delusions are largely characterised by inappropriate levels of conviction for beliefs that persist in the face of contradictory evidence. These beliefs often share similar thematic content, for example, persecution, grandiosity, or control. While the precise mechanisms underlying the development of high conviction in delusional beliefs remain unclear, research has more recently focused on the role of intuitive reasoning processes in the formation and maintenance of delusions.

In tandem, there is a robust literature investigating how repetition influences truth evaluation in healthy individuals. This phenomenon, known as the truth effect, has shown that statements that have been encountered before are more likely to be judged as true than novel statements. The primary mechanism underlying this effect is a metacognitive experience termed processing fluency (i.e., the ease or difficulty with which a stimulus is processed), which is then used intuitively as a cue for truth.

Over a series of truth effect experiments, this project explored the use of processing fluency in perceptions of truth, and how it might relate to the development of erroneous conviction as seen in clinical delusions. Specifically, the investigation sought to elucidate whether the truth effect behaved differently in response to different types of thematic content, and across individual differences in trait schizotypy or delusion-proneness.

The first empirical chapter explored whether truth judgements are influenced by the thematic content being evaluated (i.e., delusion-relevant, or neutral). Participants completed a truth effect task containing a series of delusion-relevant and neutral trivia statements, of which half were repeated once during the experiment. Contrary to expectations, the truth effect was smaller for delusion-relevant than for neutral items; however, differences in novel truth ratings between the two statement types prompted further investigation.

The second empirical chapter identified familiarity as a significant factor affecting baseline ratings in the preceding experiments. An item analysis was conducted, and a final truth effect experiment for delusion-relevant and neutral content was performed. The findings again revealed that the truth effect, if anything, was smaller for delusion-relevant items than for neutral items.

The third empirical chapter investigated whether individual differences in trait schizotypy predicted the size of the truth effect across the preceding chapters. These individual differences were also compared across the truth effect for delusion-relevant and neutral items. The findings revealed an interaction between the truth effect, delusion-relevant content, and positive trait schizotypy, whereby higher levels of positive schizotypy predicted a larger truth effect for delusion-relevant content.

The fourth and final empirical chapter investigated whether statements that are self-referential elicit a larger truth effect than content relating to another known person. These results were also examined across individual differences in trait schizotypy. However, no truth effect was observed in this instance.

This project provides a novel contribution to research surrounding the role of processing fluency in perceptions of truth among individuals who are more delusion-prone or higher in trait schizotypy, and further implicates the role of thematic content in belief formation.

Keywords: truth effect, illusory truth, repetition, delusions, schizophrenia, intuitive reasoning, intuition, belief, belief formation, metacognition, conviction, processing fluency

Subject: Psychology thesis

Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Education, Psychology and Social Work
Supervisor: Dr Oren Griffiths