Belief-bias reasoning in non-clinical delusion-prone individuals

Background and Objectives: It has been proposed that people with delusions have difficulty inhibiting beliefs (i.e., “doxastic inhibition”) so as to reason about them as if they might not be true. We used a continuity approach to test this proposal in non-clinical adults scoring high and low in psychometrically assessed delusion-proneness. High delusion-prone individuals were expected to show greater difficulty than low delusion-prone individuals on “conflict” items of a “belief-bias” reasoning task (i.e. when required to reason logically about statements that conflicted with reality), but not on “non-conflict” items. 

Methods: Twenty high delusion-prone and twenty low delusion-prone participants (according to the Peters et al. Delusions Inventory) completed a belief-bias reasoning task and tests of IQ, working memory and general inhibition (Excluded Letter Fluency, Stroop and Hayling Sentence Completion).

Results: High delusion-prone individuals showed greater difficulty than low delusion-prone individuals on the Stroop and Excluded Letter Fluency tests of inhibition, but no greater difficulty on the conflict versus non-conflict items of the belief-bias task. They did, however, make significantly more errors overall on the belief-bias task, despite controlling for IQ, working memory and general inhibitory control. 

Limitations: The study had a relatively small sample size and used non-clinical participants to test a theory of cognitive processing in individuals with clinically diagnosed delusions. 

Conclusions: Results failed to support a role for doxastic inhibitory failure in non-clinical delusion-prone individuals. These individuals did, however, show difficulty with conditional reasoning about statements that may or may not conflict with reality, independent of any general cognitive or inhibitory deficits.