Experiences and cognitive processes are two crucial elements in the formation and maintenance of delusions. Maher’s (1974) one-factor theory argues that delusions are reasonable responses to anomalous experiences. Motivated by the evidence that some people with anomalous experiences do not have delusions, the two-factor theory (e.g., Davies, Coltheart, Langdon, & Breen, 2001) argues that besides anomalous experiences, there is an impairment in the cognitive processes.
In my understanding, delusions arise not because of either anomalous experiences or impaired cognitive processes alone, but due to a mismatch between them so that the impaired cognitive processes are not able to account for the anomalous experiences in a normal way. Since a mismatch may also happen when either the experience is too anomalous for normal cognitive processes or the cognitive processes are too impaired for a normal experience, it invites us to wonder whether delusions may arise:
(1) when the anomalous experiences are so abnormal that even normal cognitive processes are not able to account for them;
(2) when the cognitive processes are so impaired that they cannot even account for normal experiences.
Here I shall argue for the idea that delusions may arise in scenario (1). Although it looks similar to Maher’s one-factor theory in the sense that they both agree that delusional people have a normal cognitive ability, they have two important differences. First, this idea relies on that our cognitive ability is limited. Second, the anomalous experiences here are something beyond a normal cognitive ability.
To illustrate how delusions might arise in this scenario, let us imagine that Jane lives in a world in which no one has the sensation of colour and there are no colour concepts and words. One day, Jane somehow has a faint sensation of colour. She looks at the red wall and notices that something is different. But, without the help of any colour concepts and words, Jane is not able to know that it is the red colour that causes the difference.
Suppose redness makes Jane feel passionate and aggressive as she feels when she listens to rock music. Without a better explanation, she hence believes that the wall secretly plays rock music to her. Likewise, Jane believes that her husband with golden hair, pink skin, and blue eyes is an imposter. In her world, Jane may be diagnosed with play-rock-music-wall delusion and Capgras delusion, though she has a normal cognitive ability.
It is an empirical question whether a certain delusion is caused by anomalous experiences or impaired cognitive processes or both. Further study is required to explore the nature of anomalous experiences and our cognitive ability. For instance, as regards the question which specific cognitive ability is limited and hence unable to account for anomalous experiences, one answer is our linguistic ability, which arguably has a limited descriptive power. It is also reflected in some delusional people’s first-person accounts:
[I]t is extremely difficult to describe such changes in words because matters are dealt with which lack all analogies in human experience and which I appreciated directly only in part with my mind’s eye, in part only by their effects, so that I may have formed but an approximate picture. (Schreber, 2000, p. 120-121)