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In this post  Kengo Miyazono  (Hiroshima) and  Ryan McKay  (Royal Holloway) summarise their new paper “ Explaining delusional beliefs: a hybrid model ”, in which they 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.  There are at least two influential candidates for a global theory of delusions (i.e., a theory that explains many kinds of delusions, rather than particular kinds of delusions such as persecutory delusions) in the recent literature: the two-factor theory (Coltheart, 2007 ; Coltheart, Menzies, & Sutton, 2010 ; Coltheart, Langdon, & McKay, 2011 ), according to which delusions are explained by two distinct neurocognitive factors with different explanatory roles, and the prediction error theory (Corlett et al., 2010 ; Corlett, Honey, & Fletcher, 2...

In this post, Phil Corlett replies to Ryan McKay 's summary of his paper " Measles, Magic and Misidentifications: A Defence of the Two-Factor Theory of Delusions ", itself a response to Phil's earlier post on his paper " Factor one, familiarity and frontal cortex: a challenge to the two-factor theory of delusions ". See also Amanda Barnier 's important commentary on the debate, and Phil's reply . Got all that? Right, on with the post! I am grateful to Ryan for his careful and collegial rebuttal of my critique. I am grateful too for the opportunity to respond. Ryan’s response does mollify some of my points. However, I am sure no one will be surprised that I have not updated my beliefs about 2-factor theory. First, Ryan suggests that 2-factor theorists knew about the breadth of the deficits of vmPFC cases, since they were described in Langdon and Coltheart’s ( 2000 ) paper. They were indeed described. Why then, 19 years (and hundreds of theory pape...

This post is by Philip Corlett who is currently engaging in a debate with Ryan McKay on this blog about the two-factor theory of delusions (see Phil's and Ryan's previous posts). Here Phil replies to Amanda Barnier's comment . I am grateful to Amanda for her contributions, to the blog exchange and to the literature on delusions. I am of course aware of her hypnosis work – having spent time at Macquarie and even been hypnotized (I am highly hypnotizable, which is perhaps too much to share here). My article and post were provocative and perhaps too confrontational. Having spent time at the Belief Formation Program Table, I understand how exciting and generative it can be. My word choice was perhaps a little too strong. 'Adherents' may have been better. I see that 'acolytes' may be particularly insulting to practicing scientists. My article was about the basic foundational data and arguments of two-factor theory. Whilst Amanda is right to criticize my word ch...

This post is by Amanda Barnier , Professor of Cognitive Science and Associate Dean Research in the Faculty of Human Sciences at Macquarie University . She was Deputy Leader of the Belief Formation Program and Chief Investigator of the Australian Research Council (ARC) Centre of Excellence in Cognition and its Disorders from 2011-2018. In her work she has attempted to use hypnotic methods to recreate clinical delusions in the laboratory. Here she contributes to the exchange between Phil Corlett and Ryan McKay on the two-factor theory of delusions. I read Phil Corlett ’s and Ryan McKay ’s blog posts with great interest as well as their original article and commentary . As someone who has worked in the field of delusions (albeit on a bit of a hypnotic tangent) for about 15 years (including for 12 years since I arrived at Macquarie University in 2007 to work with Max Coltheart), I wanted to share some insights. In his original published article in Cognitive Neuropsychiatry, Phil describ...

I'm Ryan McKay , Professor of Psychology at Royal Holloway, University of London , and head of the Royal Holloway Morality and Beliefs Lab (MaB-Lab) . I'm interested in how we form and revise beliefs, including delusional beliefs. This post is a summary of my article “Measles, Magic and Misidentifications: A Defence of the Two-Factor Theory of Delusions” in reply to Phil Cortlett's recent paper discussed on the blog last week . The Two-Factor Theory of Delusions One may (a) interpret data falsely, but also (b) receive false data for interpretation. ~ Southard, 1912 , p. 328. The idea that delusions arise when individuals attempt to interpret “false data” has been incorporated in several theories of delusions. Two-factor theorists, however (e.g., Coltheart et al., 2011; Davies & Coltheart, 2000 ; Langdon & Coltheart, 2000 ), view deluded individuals both as “receiving false data for interpretation” (factor one, which furnishes the content of the delusion) and as “...

In this post,  Phil Corlett , Associate Professor of Psychiatry at Yale School of Medicine, discusses some of the ideas in his  paper  ‘Factor one, familiarity and frontal cortex: a challenge to the two-factor theory of delusions’ recently published in the Journal of Cognitive Neuropsychiatry. Over recent years, Imperfect Cognitions has become the premier hub and outlet for work on the neurobiology and cognitive psychology of delusions. It has featured my work on aberrant prediction error and delusions in schizophrenia (Corlett et al., 2007 ), and work that conceptually replicates it (Kaplan et al., 2016 ). There has been work, also highlighted on the blog, from neurological patients that suggest instead that a 2-factor explanation of delusions may be more appropriate (Darby et al., 2017 ), although that work was not conclusive (McKay and Furl, 2017 ). It has all garnered much interest. Partly because delusions inherently fascinating, I think, and partly because the argum...

Today's post is by Kengo Miyazono , Hiroshima University, who talks about his latest book, Delusions and Beliefs (Routledge 2018). This book addresses the following theoretical questions about delusions: (1) The Nature Question : What is a delusion? In particular, what kind of mental state is it? The standard view in psychiatry is that delusions are beliefs. But, is this view (‘doxasticism about delusion’) really true? Delusions have a number of peculiar features that are not belief-like, such as the remarkable insensitivity to evidence. Are these peculiar features consistent with the doxastic conception of delusions? (2) The Pathology Question : Delusions are pathological mental states. Delusions, together with other symptoms, warrant clinical diagnoses and treatments. Why are delusions pathological? What distinguishes pathological delusions from non-pathological irrational beliefs? Are delusions pathological because they are too irrational? Or, are they pathological because they...

In September 2018, a team of Birmingham philosophers, comprising Kathy Puddifoot , Valeria Motta , Matilde Aliffi , EmaSullivan-Bissett and myself , were in sunny Rijeka, Croatia, to talk a whole lot of Epistemic Innocence at the European Society for Philosophy and Psychology . Epistemic innocence is the idea at the heart of our research at Project PERFECT . A cognition is epistemically innocent if it is irrational or inaccurate and operates in ways that could increase the chance of acquiring knowledge or understanding, where alternative, less costly cognitions that bring the same benefits are unavailable. Over the last few years, researchers on the project and beyond have investigated the implications of epistemic innocence in a range of domains (see a list of relevant work here ). Our epistemic innocence symposium at ESPP2018 was a mark of the relative maturity of the concept, and the opportunity for us to start expanding its applications.        ...

This post is by  Eisuke Sakakibara , psychiatrist working at  The University of Tokyo Hospital . In this post he writes about his paper “ Intensity of experience: Maher’s schizophrenic delusion revisited ” recently published in Neuroethics. Delusion is one of the most frequently discussed themes in philosophy of psychiatry, and this is my second publication regarding delusions. In my first paper, entitled “ Irrationality and pathology of beliefs ,” I proposed that not all delusions are pathological, and some delusions are formed without any physical or mental dysfunction. In my second paper , I focused on delusions accompanied by schizophrenia. As for schizophrenic delusions, it is beyond question that they are the result of dysfunction of some kind. The problem, then, is what kind of dysfunction is relevant for the development of schizophrenic delusions. The theory of schizophrenic delusion has developed by the consecutive works made by Brendan Maher. He proposed in 1974 th...

Stephen Gadsby  is a PhD candidate in the  Cognition and Philosophy lab , Monash University. His research spans a number of topics, including anorexia nervosa, body representation, delusions, psychiatric taxonomy, mental representation and predictive processing. In this post, he summarises his  new paper  "Self-Deception and the Second Factor: How Desire Causes Delusion in Anorexia Nervosa" recently published in Erkenntnis. Research shows that anorexia patients don’t hold extreme body ideals, despite common misconception. Indeed, most patients are thinner than what they judge their ideal size to be. In this paper , I advance a two-factor explanation for why patients believe they haven’t yet reached their ideal size. This account attempts to answer two questions: how the content of this belief arises and why the belief is maintained in the face of contradictory evidence. Following from previous work (Gadsby 2017a ; 2017b ), I answer the first of these question by sugg...