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In recent times, explanations of the Capgras delusion have tended to emphasise the cognitive dysfunction that is believed to occur at the second stage of two-stage models. This is generally viewed as a response to the inadequacies of the one-stage account. Whilst accepting that some form of cognitive disruption is a necessary part of the aetiology of the Capgras delusion, I nevertheless argue that the emphasis placed on this second-stage is to the detriment of the important role played by the phenomenology underlying the disorder, both in terms of the formation and maintenance of the delusional belief. This paper therefore proposes an interactionist two-stage model in which the phenomenal experience of the Capgras patient is examined, emphasised, and its relation to top-down processing discussed.

We proceed to describe a model for the formation and maintenance of polythematic delusions encountered in schizophrenia, which is in adequacy with Brendan Maher's account of delusions. Polythematic delusions are considered here as the conclusions of arguments triggered by apophenia that include some very common errors of reasoning such as post hoc fallacy and confirmation bias. We describe first the structure of reasoning which leads to delusions of reference, of telepathy and of influence, by distinguishing between the primary, secondary, tertiary and quaternary types of delusional arguments. These four levels of arguments correspond to a stage the nature of which is respectively instantial, inductive, interpretative at a monothematic level and interpretative at a polythematic level. We also proceed to identify accurately the fallacious steps in the corresponding reasoning. We expose then the role of apophenia in the elaboration of delusional ideas. Lastly, we describe the role played by the hallucinations in the present model.

Stanford Encyclopedia Entry on Delusions.

Current models of delusion converge in proposing that delusional beliefs are based on unusual experiences of various kinds. For example, it is argued that the Capgras delusion (the belief that a known person has been replaced by an impostor) is triggered by an abnormal affective experience in response to seeing a known person; loss of the affective response to a familiar person’s face may lead to the belief that the person has been replaced by an impostor (Ellis & Young, 1990). Similarly, the Cotard delusion (which involves the belief that one is dead or unreal in some way) may stem from a general..

In this paper the role of incomprehensibility in the conceptualization of the DSM-IV definition of delusion is discussed. According to the analysis, the conceptual dependence of DSM-IV definition of delusion on incomprehensibility is manifested in several ways and infested with ambiguity. Definition of bizarre delusions is contradictory and gives room for two incompatible readings. Also the definition of delusion manifests internal inconsistencies and its tendency to account for delusions in terms of misinterpretation is bound to miss the content of the traditional comprehension of delusionality. It is suggested that the ambiguities in defining delusions has to do with the question whether psychiatric practice is better accounted for in terms of the grammar of incorrectness or of incomprehensibility.

1923; Young, this volume); the Cotard delusion (Cotard, 1882; Berrios and Luque, 1995; Young, this volume); the Fregoli delusion (Courbon and Fail, 1927; de Pauw, Szulecka and Poltock, 1987; Ellis, Whitley and Luaute´, 1994); the delusion of mirrored-self misidentifi- cation (Foley and Breslau, 1982; Breen et al., this volume); a delusion of reduplicative param- nesia (Benson, Gardner and Meadows, 1976; Breen et al., this volume); a delusion sometimes found in patients suffering from unilateral neglect (Bisiach, 1988); and the delusions of alien control and of thought insertion, which are characteristic of schizophrenia (Frith, 1992).

Delusional beliefs have sometimes been considered as rational inferences from abnormal experiences. We explore this idea in more detail, making the following points. Firstly, the abnormalities of cognition which initially prompt the entertaining of a delusional belief are not always conscious and since we prefer to restrict the term “experience” to consciousness we refer to “abnormal data” rather than “abnormal experience”. Secondly, we argue that in relation to many delusions (we consider eight) one can clearly identify what the abnormal cognitive data are which prompted the delusion and what the neuropsychological impairment is which is responsible for the occurrence of these data; but one can equally clearly point to cases where this impairments is present but delusion is not. So the impairment is not sufficient for delusion to occur. A second cognitive impairment, one which impairs the ability to evaluate beliefs, must also be present. Thirdly (and this is the main thrust of our chapter) we consider in detail what the nature of the inference is that leads from the abnormal data to the belief. This is not deductive inference and it is not inference by enumerative induction; it is abductive inference. We offer a Bayesian account of abductive inference and apply it to the explanation of delusional belief.

In his classic paper, “Delusional thinking and perceptual disorder,” Brendan Maher (1974) argues that psychiatric delusions are hypotheses designed to explain anomalous experiences, and are “developed through the operation of normal cognitive processes.” Consider, for instance, the Capgras delusion. Patients suffering from this particular delusion believe that someone close to them—such as a spouse, a sibling, a parent, or a child—has been replaced by an impostor: by someone who bears a striking resemblance to the “original” and who (for reasons unknown) is intent on passing herself off as that individual. On Maher's view, the “Impostor Hypothesis” is the response of a rational agent to the anomalous experience it is invoked to explain. Recently, a number of philosophers have argued that Maher's analysis of delusion doesn't work when applied to the Capgras delusion. In this paper, I defend Maher's analysis against these arguments. However, my aim is not merely to defend Maher's analysis, but also to draw attention to some of the methodological problems that have led to its hasty dismissal.

Some otherwise rational people appear to believe strange things. Sometimes people believe that someone, usually a near relative or member of their family - often their spouse - has been replaced by an impostor. Sometimes people believe that they are dead. These two delusions – known as the Capgras and Cotard delusion respectively – are instances of monothematic delusions, for they are limited to very specific topics. Other monothematic delusions involve the delusion that one is being followed by known people in disguise (the Frégoli delusion), or that the person one sees in the mirror is someone else (mirrored-self misidentification). We will focus on the Capgras delusion.

Subjects with delusions profess to believe some extremely peculiar things. Patients with Capgras delusion sincerely assert that, for example, their spouses have been replaced by impostors. Patients with Cotard’s delusion sincerely assert that they are dead. Many philosophers and psychologists are hesitant to say that delusional subjects genuinely believe the contents of their delusions.2 One way to reinterpret delusional subjects is to say that we’ve misidentified the content of the problematic belief. So for example, rather than believing that his wife is has been replaced by an impostor, we might say that the victim of Capgras delusion believes that it is, in some respects, as if his wife has been replaced by an impostor. Another is to say that we’ve misidentified the attitude that the delusional subject bears to the content of their delusion. So for example, Gregory Currie and co-authors have suggested that rather than believing that his wife has been replaced by an impostor, we should say that the victim of Capgras delusion merely imagines that his wife has been replaced by an impostor.3.