DELUSIONS AND BRAIN INJURY - THE PHILOSOPHY AND PSYCHOLOGY OF BELIEF

Circumscribed delusional beliefs can follow brain injury. We suggest t hat these involve anomalous perceptual experiences created by a defici t to the person's perceptual system, and misinterpretation of these ex periences due to biased reasoning. We use the Capgras delusion (the cl aim that one or more of one's close relatives has been replaced by an exact replica or impostor) to illustrate this argument. Our account ma intains that people voicing this delusion suffer an impairment that le ads to faces being perceived as drained of their normal affective sign ificance, and an additional reasoning bias that leads them to put grea ter weight on forming beliefs that are observationally adequate rather than beliefs that are a conservative extension of their existing stoc k. We show how this position can integrate issues involved in the phil osophy and psychology of belief, and examine the scope for mutually be neficial interaction.