After reviewing factors implicated in the generation of delusional beliefs, we conclude that whilst a perceptual aberration coupled with a particular type of attri‐butional bias may be necessary to explain the specific thematic content of a bizarre delusion, neither of these factors, whether in isolation or in combination, is sufficient to explain the presence of delusional beliefs. In contrast to bias models (theories which explain delusion formation in terms of extremes of normal reasoning biases), we advocate a deficit model of (...) delusion formation–that is, delusions arise when the normal cognitive system which people use to generate, evaluate, and then adopt beliefs is damaged. Mere bias we think inadequate to explain bizarre delusions which defy commonsense and persist despite overwhelming rational counter‐argument. In particular, we propose that two deficits must be present in the normal cognitive system to explain bizarre delusions: (1) there must be some damage to sensory and/or attentional‐orient‐ing mechanisms which causes an aberrant perception–this explains the bizarre content of the causal hypothesis generated to explain what is happening; and (2) there must also be a failure of normal belief evaluation–this explains why a hypothesis, implausible in the light of general commonsense, is adopted as belief. This latter deficit occurs, we suggest, when an individual is incapable of suspending the natural favoured status of direct first‐person evidence in order to critically evaluate hypotheses, given equal pri‐ority whether based on direct or indirect sources of information. In contrast, delusions with ‘ordinary’ content may arise when a single deficit of normal belief evaluation occurs in the context of an extreme (but normal) attentional bias, thus causing failure to critically evaluate hypotheses based on misperceptions and misintrepretations of ambiguous (but ordinary) first‐person experience. (shrink)

This article contrasts the cognitive neuropsychiatric approach with the traditional psychiatric approaches to delusions to develop testable cognitive theories of delusions so as to render the generation of delusions psychologically understandable. It illustrates how cognitive neuropsychiatrists use the Bruce and Young model of face processing to explain the generation of misidentification delusions. The study of facial expression highlights that future cognitive neuropsychiatric study of self and non-self face processing using different representational media in patients with mirrored-self misidentification delusions will likely (...) be informative with regard to advancing scientific understanding of the putative differences between self and non-self recognition. It reviews cognitive neuropsychiatric research into the Capgras delusion and shows the distinction between overt face recognition and person identity authentication, and suggests the need for further modification of Bruce and Young's model to remove direct pathways between the person's identity module and the affective response system and to incorporate a separate integrative device. (shrink)

Four detailed cases of delusions of misidentification (DM) are presented: two cases of misidentification of the reflected self, one of reverse intermetamorphosis, and one of reduplicative paramnesia. The cases are discussed in the context of three levels of interpretation: neurological, cognitive and phenomenological. The findings are compared to previous work with DM patients, particularly the work of Ellis and Young (1990; Young, 1998) who found that loss of the normal affective response to familiar faces was a contributing factor in the (...) Capgras delusion. The four cases presented suggest that this particular deficit is not a critical factor in the development of other forms of DM. (shrink)

[This download contains the Table of Contents and Chapter 1.] This first book-length study of confabulation breaks ground in both philosophy and cognitive science.