Delusional misidentification of inanimate objects: a literature review and neuropsychological analysis of cognitive deficits in two cases.

Following a brief review of the literature on Delusions of Inanimate Doubles (DID), compared with other similar delusions, two cases are presented. Each completed a battery of tests designed to explore their cognitive abilities. In both cases, familiar and unfamiliar face-processing skills remained intact and word memory was unaffected.

Delusions demand attention.

We used a variant of the Stroop paradigm to investigate attention bias in a young woman (JK) with delusional beliefs that she had died and that members of her family had changed. JK was shown sets of words printed in different colours of ink, and was asked to name the colour of each word. Sets of words were chosen which related to her delusions, and to possible contributory moods.

The Capgras and Cotard delusions.

We explore the relation between the Capgras delusion (the belief that your relatives have been replaced by impostors) and the Cotard delusion (the delusional belief that you have died). At first sight, these delusions would seem to have little to do with each other, except that they both involve bizarre claims about existence (for self or others). On closer examination, however, there are other parallels.

Face processing impairments and delusional misidentification.

We report detailed investigations of the face processing abilities of four patients who had shown symptoms involving delusional misidentification. One (GC) was diagnosed as a Frégoli case, and the other three (SL, GS, and JS) by symptoms of intermetamorphosis. The face processing tasks examined their ability to recognize emotional facial expressions, identify familiar faces, match photographs of unfamiliar faces, and remember photographs of faces of unfamiliar people.

Dangerous delusions. Violence and the misidentification syndromes.

Among the mentally ill, those with well-developed delusions are more likely to commit violent crimes against persons than those with chronic, undifferentiated psychoses. Reports of violence associated with delusional misidentification are reviewed and four patients described who were either perpetrators or victims of assaults as a consequence of the syndromes of Frégoli, Intermetamorphosis, Subjective Doubles and Capgras. The cases illustrate the multiplicity of factors which have to be taken into consideration in order to predict whether an individual will act in a violent manner on these delusions.