Subclinical delusional ideation and reasoning

Abstract

Delusions are fixed beliefs that are not amenable to change in light of conflicting evidence (APA, 2013) and are a symptom most often associated with schizophrenia. Evidence suggests that psychotic symptoms, such as delusions, exist on a continuum from the healthy population to clinical disorder (van Os, Linscott, Myin-Germeys, Delespaul & Krabbendam, 2009; van Os & Reininghaus, 2016). Research demonstrating that biases in reasoning contribute to the formation of such delusional beliefs has gathered momentum and has been shown in both clinical and healthy, non-clinical populations (e.g. Warman, Lysaker, Martin, Davis, & Haudenschield, 2007). Liberal acceptance has only been demonstrated previously in patients with schizophrenia therefore the current thesis aimed to examine whether a liberal acceptance reasoning style would be evident in a subclinical sample consistent with a continuum model and to examine factors that may underpin this acceptance. In Chapters 3-5 and Chapter 8, it was found that there was a tendency for those high in delusional ideation to rate stimuli with both delusional and neutral content as more likely to be true compared to those low in delusional ideation indicating a lowered threshold for plausibility, consistent with a liberal reasoning style. It was a fairly consistent finding that stimuli with delusional themes were rated as more exciting than stimuli with neutral themes by participants high in delusional ideation, highlighting a potential mechanism for why narratives with delusional and neutral content are more likely to be accepted (Chapter 2, 5 & 8). Sensation seeking however did not provide an explanation for finding excitement in delusional stimuli and creativity was only implicated when this was in regards to emotional creativity in Chapter 3. Furthermore, perceptual and non-perceptual apophenia (the tendency to see patterns where none exist or make causal connections between random events) appears to play a central role in why participants high in delusional ideation liberally accept. Embedded objects were reported in visual ‘noise’ where no object had been embedded by participants high in delusional ideation in Chapter 4. Consistent with this, participants high in delusional ideation also tended to report experiencing more coincidences than those low in delusional ideation in Chapters 5 and 8. This is important for the liberal acceptance account since the ability to see patterns where none exist and make causal connections between random events may be a factor in why delusion-prone individuals see plausibility where others do not. Liberal acceptance was also investigated in light of findings from studies with clinical patients in Chapters 6 and 7. In Chapter 6, participants assigned plausibility ratings to interpretations of ambiguous pictures to see if those high in delusional ideation see plausibility in interpretations that others would reject or rate lowly. Similar trends were found in a subclinical sample, to that found in Moritz and Woodward’s (2004) original study and participants high in delusional ideation rated more of the interpretations as possible, good or excellent compared to participants low in delusional ideation, who rated more of the interpretations as poor; these effects however did not achieve significance. When probability estimates and decision and rejection thresholds were examined using the ‘Who Wants to be a Millionaire?’ paradigm (see Moritz, Woodward & Hausmann, 2006), differences between participants high and low in delusional ideation did not emerge in Chapter 7. The series of experiments reported in this thesis have been successful in highlighting under what conditions participants high in delusional ideation liberally accept and in identifying potential factors that underpin this acceptance. Limitations of this research, theoretical implications and directions for future research are considered in the General Discussion in Chapter 8.