PPIG: Philosophy, Psychology, and Informatics Group

Presenter: Kengo Miyazono

Title: A Hybrid Theory of Delusion Formation

Abstract: Delusions are unjustified beliefs, often with bizarre content, that feature in an array of psychiatric and neurological disorders, including schizophrenia, dementia, and traumatic brain injury. This paper presents and defends a hybrid theory of the formation of delusions that incorporates the central ideas of two particularly influential theories in the literature: the two-factor theory and the prediction-error theory. According to the two-factor theory, delusions stem from the conjunction of two neurocognitive factors, the first of which accounts for the content of the delusional belief (e.g., “my spouse has been replaced by an impostor”), and the second of which accounts for why a belief with that content is adopted and maintained despite the evidence against it. According to the prediction-error theory, delusions stem from disturbances in the processing of prediction errors (mismatches between expectations and actual inputs). In particular, delusions are conceived as attempts to accommodate inappropriately generated prediction error signals. Although these theories are typically regarded as incompatible with one another, we show that this need not be the case. According to the hybrid theory we advance, the development of a delusion is explained by the presence of some kind of misleading prediction-error (the first factor), responsible for the theme of the delusion; coupled with the overestimation of the precision of this prediction-error (factor two), responsible for its adoption and maintenance. The theory, as a hybrid, inherits theoretical and empirical merits of the two-factor and prediction-error theories and provides a unified account of delusions in a wide variety of conditions.