Conscious Experience and Delusional Belief

Keywords
delusion, belief, consciousness, Capgras, cognitive neuropsychiatry

In their interesting analysis of types of accounts of the Capgras delusion, Fine, Craigie, and Gold contrast two approaches to theorizing about delusional belief, which they call the "explanation" approach and the "expression" or "endorsement" approach.

The central idea for the "expression" or "endorsement" approach is that when an intact individual perceives his wife, the perceptual representation that is evoked in that man by the wife is a rich one in the sense that it includes conceptual content such as, "This is my wife." In the Capgras patient, the perceptual representation of the wife includes the content "That is not my wife." As Fine, Craigie, and Gold (2005, 148) say, "'Expression' accounts require an explanation of the deficit causing the experience that a familiar person (or object) has been replaced . . . Without such an explanation, 'expression' accounts have no explanatory power." This is indeed conceded by Bayne and Pacherie (2004, 4): "We need to explain how a perceptual state could have this content without inheriting it from the belief that the person one is looking at is not the person one remembers as one's wife." It therefore seems to me that this approach requires much more fleshing out before it will be possible to decide whether it is a viable competitor to the "explanation" account; from here on I only consider the "explanation" account.

According to the explanation account put very generally, in any case of monothematic delusion a state of the world has arisen for which the patient has to find an explanation, and the delusional belief provides such an explanation: that is, if the delusional belief were true, then it would follow that the world would be the way it now seems to be to the patient. In this sense, the belief explains why the world is as it now seems to be. Thus, in the specific case of the Capgras delusion, the new state of the world that has arisen is that there is a person in the world who looks exactly like one's wife but when that person is seen there is little or no arousal of one's autonomic nervous system—the degree of response is that which is characteristic of observing a stranger. This datum is just what one would expect to observe if the person being seen is indeed a stranger (despite her physical resemblance to one's wife).

My colleagues and I (see Coltheart [2005] for a summary) have argued that, for a number of different kinds of monothematic delusion, one can identify neuropsychological deficits that present the patient with new states of the world, and one can plausibly argue that the content of any particular patient's delusion represents an attempt at explaining why the world is as it now seems to be to this patient. Here are four examples:

1. Mirrored-self misidentification, Case T: This man's delusion was that the person he saw when he looked in the mirror was not him, but some stranger. Breen et al. (2000) showed that T also suffered from mirror agnosia—a loss of the ability to understand how mirrors work. For him, a mirror was a window, or a hole in the wall. If this is so, then anyone he sees in a mirror must be occupying a different part of the world than he; and therefore must be a different person than he.
2. Mirrored-self misidentification, Case F: This man's delusion was also that the person he saw when he looked in the mirror was not him, but some stranger. Breen et al. (2000) showed that F also suffered from impairments in face perception, so when he now looked at his face in the mirror the perceptual representation thus generated would not properly match the stored representation of his face that he acquired before his face perception became impaired. If this were so, then the person he saw in the mirror would not look like him; and therefore...