Delusional Inference

Abstract

Does the formation of delusions involve abnormal reasoning? According to the prominent ‘two‐factor’ theory of delusions (e.g. Coltheart, 2007), the answer is yes. The second factor in this theory is supposed to affect a deluded individual's ability to evaluate candidates for belief. However, most published accounts of the two‐factor theory have not said much about the nature of this second factor. In an effort to remedy this shortcoming, Coltheart, Menzies and Sutton (2010) recently put forward a Bayesian account of inference in delusions. I outline some criticisms of this important account, and sketch an alternative account of delusional inference that, I argue, avoids these criticisms. Specifically, I argue that the second factor in delusion formation involves a systematic deviation from Bayesian updating, a deviation that may be characterized as a bias towards ‘explanatory adequacy’. I present a numerical model of this idea and show that my alternative account is broadly consistent with prominent prediction error models of delusion formation (e.g. Corlett, Murray et al., 2007).

Usefulness of models in the process of qualifying contents as delusional – case analysis

“…The authors of the paper assume that the inference process will be perceived as impaired in the event of right hemisphere lesions. More detailed models of inference within the frames of delusion formation can be found in the literature [6,19]. It seems that the existence of any circumstances which may affect the evaluation of the data in the course of belief formation should be a diagnostic clue.…”

“…Thus, the concept assumes that there is a region located in the right hemisphere of the brain whose damage results in "disinhibition" of the rejection of beliefs that in the absence of the damage would not be accepted as true. An overview of specific deficits that do not lead perforce to the occurrence of delusional beliefs is included in work by McKay [6].…”

“…Archives of Psychiatry and Psychotherapy, 2015; 2: [5][6][7][8][9][10][11][12] people could communicate telepathically. This was not disturbing for him, nor did it dominate his thoughts.…”

The erotetic theory of delusional thinking

“…al. 2010) whereas others claims the subject's prior in that hypothesis is low and therefore discounted in her subsequent reasoning (McKay, 2012).…”

“…al., 2010;McKay, 2012;Davies and Egan, 2013). Since we know that a Capgras subject actually believes an "imposter" hypothesis, we can conclude that the subject's ratio of posterior probabilities favours it over alternative hypotheses.…”