Measles, magic and misidentifications: a defence of the two-factor theory of delusions

In defense of the one-factor doxastic account: A phenomenal account of delusions

According to the doxastic model, delusions are beliefs. In the metacognitive model, delusions are imaginings mistaken for beliefs. I argue that endorsement of false second-order beliefs could also create unpleasant dissonance, that mentally healthy people often endorse irrational or conflicting beliefs, and that the lack of delusion-motivated action can be explained by the influence of nonbelief factors on action. The two-factor doxastic model posits irrationality as necessary, and one metric of rationality many scholars employ is whether a response is easily understood by folk psychology. A precedent for folk-psychological acceptance of contextually bizarre beliefs as a result of personal experience can already be found in the lack of imaginative resistance encountered not in response to the impossibilities portrayed in speculative fiction, but in response to the characters' ability to incorporate these occurrences into their mental frameworks, despite them often being at odds with these characters' bedrock understanding of the world.

Delusions beyond beliefs: a critical overview of diagnostic, aetiological, and therapeutic schizophrenia research from a clinical-phenomenological perspective

Delusions are commonly conceived as false beliefs that are held with certainty and which cannot be corrected. This conception of delusion has been influential throughout the history of psychiatry and continues to inform how delusions are approached in clinical practice and in contemporary schizophrenia research. It is reflected in the full psychosis continuum model, guides psychological and neurocognitive accounts of the formation and maintenance of delusions, and it substantially determines how delusions are approached in cognitive-behavioural treatment. In this Review, we draw on a clinical-phenomenological framework to offer an alternative account of delusion that incorporates the experiential dimension of delusion, emphasising how specific alterations to self-consciousness and reality experience underlie delusions that are considered characteristic of schizophrenia. Against that backdrop, we critically reconsider the current research areas, highlighting empirical and conceptual issues in contemporary delusion research, which appear to largely derive from an insufficient consideration of the experiential dimension of delusions. Finally, we suggest how the alternative phenomenological approach towards delusion could offer new ways to advance current research and clinical practice.

Explaining delusional beliefs: a hybrid model

Introduction: In this paper we present and defend a hybrid theory of the development of delusions that incorporates the central ideas of two influential (yet sometimes bitterly opposing) theoretical approaches to delusions-the two-factor theory and the prediction error theory. Method: After introducing the central ideas of the two-factor theory and the prediction error theory, we describe the motivations for our conciliatory project, explain the theoretical details of the hybrid theory we propose, and answer potential objections to our proposal. Results: According to the hybrid theory we advance, the first factor of a delusion is physically grounded in an abnormal prediction error, and the second factor is physically grounded in the overestimation of the precision of the abnormal prediction error. Against anticipated objections, we argue that the hybrid theory is internally coherent, and that it constitutes a genuine hybrid between the two-factor theory and the prediction error theory. Conclusion: A rapprochement between the two-factor theory and the prediction error theory is both possible and desirable. In particular, our hybrid theory provides a parsimonious and unified account of delusions, whether monothematic or polythematic, across a wide variety of medical conditions.

Continuing commentary: challenges or misunderstandings? A defence of the two-factor theory against the challenges to its logic

Corlett, P. R. (2019. Factor one, familiarity and frontal cortex: A challenge to the two-factor theory of delusions. Cognitive Neuropsychiatry, 24(3), 165-177. doi: 10.1080/13546805.2019.1606706 ) raises two groups of challenges against the two-factor theory of delusions: One focuses on weighing "the evidence for … the two-factor theory"; the other aims to question "the logic of the two-factor theory" (ibid., p. 166). McKay, R. (2019. Measles, magic and misidentifications: A defence of the two-factor theory of delusions. Cognitive Neuropsychiatry, 24(3), 183-190. doi: 10.1080/13546805.2019.1607273 ) has robustly defended the two-factor theory against the first group. But the second group, which Corlett believes is in many aspects independent of the first group and Darby, R. R. (2019. A network-based response to the two-factor theory of delusion formation. Cognitive Neuropsychiatry, 24(3), 178-182. doi: 10.1080/13546805.2019.1606709 , p. 180) takes as "[t]he most important challenge to the two-factor theory raised by Dr. Corlett", has by large remained. Here I offer my two cents in response to the second group. More specifically, I argue that Corlett's challenges to the logic of the two-factor theory, concerning modularity, double dissociation and cognitive penetration, seem to be based on some misunderstandings of the two-factor theory.