We explore the relation between the Capgras delusion (the belief that your relatives have been replaced by impostors) and the Cotard delusion (the delusional belief that you have died).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. Here, we summarise similarities in associated impairments of face perception, and argue that both delusions reflect an interaction of impairments at two levels. One set of contributory factors involves perceptual impairment, or anomalous perceptual experience. The other factors lead to an incorrect interpretation of this, for which we offer an explanation in terms of attribution theory. Although the Capgras and Cotard delusions are phenomenally distinct, they may therefore represent attempts to make sense of fundamentally similar experiences.

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 times taken by JK to colour-name words in these lists were compared with her times to colour-name sets of neutral words. There were three separate testing sessions which took place over a two-year period. In comparison to her times to name the colours of words in the neutral lists, JK was significantly slower to colour-name test lists containing words related to her delusional beliefs. When she was no longer experiencing these delusions, however, she was no slower to colour-name any of the test word lists. The results indicate that the Stroop paradigm can be useful in investigating individual cases of delusions and in monitoring changes in attentional bias over time.