McKay, R.
Department of Psychology, Royal Holloway University of London, Egham, UK
Deluded individuals hold beliefs unwarranted by available evidence and jeopardizing their prospects in some way. Such beliefs can stem from clinical abnormalities in cognitive processes, but may also arise via ordinary operation of such processes, coupled with the social diffusion of information. Examples include cases of mass hypochondria (e.g., epidemics of Koro, the belief that one's genitals are retracting into one's body). We call such examples \"shared delusions\". We allowed participants to learn from each other in the face of a common uncertainty, state-dependent error costs, and a subtle framing manipulation activating the concept of intentional agency. In the end, incorrect choices often spread in social groups. The result was a profusion of persistent, error-prone social traditions involving choices resulting in substantial losses. Such traditions may not quite qualify as delusions, but do represent collective errors, transmitted from one person to another, with potentially far-reaching social, political and economic repercussions.