Delusional Beliefs, Two Factor Theories, and Bizarreness
In order to explain delusional beliefs, one must first consider what factors should be included in a theory of delusion. Unlike a one factor theory, a two factor theory of delusion argues that not only anomalous experience (the first factor) but also an impairment of the belief evaluation system (the second factor) is required. Recently, two factor theorists have adopted various Bayesian approaches in order to give a more accurate description of delusion formation. By reviewing the progression from a one factor theory to a two factor theory, I argue that in light of the second factor's requirements, different proposed impairments can be unified within a consistent belief evaluation system. Under this interpretation of the second factor, I further argue that the role of a mechanism responsible for detecting bizarreness is wrongly neglected. I conclude that the second factor is a compound system which consists of differing functional parts, one of which functions to detect bizarreness in different stages of delusion; moreover, I hold that the impairment can be one or several of these functional parts.