Theories of Delusions and Their Treatment
The introductory material to this page is on the Creation of Delusion web page. .
There is a theory of delusions that separates normals from the mentally ill and that is the theory of Maher B. A. (1974, Delusional Thinking and perceptual disorder. Journal of Individual Psychology, 30, 98-113). He proposed that a delusional individual suffers from primary perceptual anomalies, fundamentally biological in nature e.g. hallucinations or strange sensations. Maher argues that the individual, seeks an explanation which is then developed by processes of reasoning that are entirely normal. Test of the reasoning of people who suffer from delusions show it to be mostly normal with the difference being that delusional people tend to jump to conclusions more than normals. These test support Maher's arguments. Maher argues that the delusion is maintained in the same way as any other strong belief; just as scientists are resistant to disconfirmation of their theories, so are deluded people equally resistant. Furthermore, he suggests that delusional beliefs are reinforced by the anxiety reduction which accompanies the development of an explanation for disturbing or puzzling experiences.
Chris Frith (British Journal of Clinical Psychology, 1999 38,319-21) wrote that:
It follows from Maher's hypothesis that delusions follow from a normal explanation of an abnormal experience. Direct evidence that this is not the case comes from two sources. First there are generated abnormal experiences which have been hypothesized as associated with delusions of control by distorting the sound of the speaker's voice (Cahill, Silbersweig and Frith, Cognitive Neuropsychiatry 1, 201-211, 1996) This manipulation induced delusional attributions in patients in an acute phase of schizophrenia. ("I hear the devil speaking when I speak"), but not in normal controls or patients who were symptom free ("you are distorting my voice with that box") Second, abnormal experiences are a frequent consequence of brain damage, but do not typically produce delusional explanations. A striking example is the "anarchic hand" (Marchetti & Della Salla,Cognitive Neuropsychiatry, 3, 191-209, 1998) This is a sign that sometimes follows unilateral damage to supplementary motor area and the corpus callosum. The hand opposite the lesion performs inappropriate low level actions not in accord with the patient's will, such as grasping door knobs or scribbling with a pencil. The patient typically tries to prevent the hand from doing these things, but does not develop delusions that the hand is controlled by alien forces. This is in striking contrast to the patient with delusions of control associated with schizophrenia. In this case the patient will report that his or her actions are being controlled by alien forces even though the actions being produced are appropriate and correctly performed (e.g. Spence et al., Brain, 120, 1997-2011, 1997)
There appears to be a contradiction here. On the one hand studies have shown that delusional people reason like normals. On the other hand Chris Frith is citing studies that show that delusional people draw different conclusions than normals. Why is this? There is a crucial difference between these studies. In one reasoning is tested in a situation where prior false assumptions of the patient do not come in to play. For example a patient might be told that there are two bottles one 3/4 full of black balls and 1/4 full with white balls and the other 3/4 full of white balls and 1/4 full of black balls and then asked questions such as if 3 balls are pulled out of a bottle and they are all black which bottle is the likely one that the person is pulling balls from. A patient is unlikely to have prior assumptions that will affect his conclusions in this type of experiment. In the speech distorting experiment prior assumptions are likely to come in to play. If one starts with the prior assumption that there is a devil and the devil is against oneself and trying to take control of oneself then the idea that the devil is controlling one's voice is not so far fetched. If one is in a paranoid frame of mind, paranoid explanations seem more probable. By paranoid frame of mind I mean an emotional state that one is under attack and that others are hostile. Also if one has developed a system of paranoid delusions already than the paranoid explanation that fits those delusions seems the most probable. One would expect someone who believes that hostile aliens are attacking him to believe that aliens are controlling his hand if he had an anarchic hand. I know a delusional person who performs well at a computer job which requires logical thinking, yet when he has headaches he believes it is a result of his being poisoned. If one already believes that one is being poisoned then it is not a big leap to think that a headache one is experiencing is the result of poison that was put in one's food. Paranoid conclusions are reasonable if one starts with paranoid assumptions.
From the point of view of this article one aspect of Maher's theory is especially important and that is a delusion and perhaps an entire system of delusional beliefs can arise from trying to explain one abnormal experience. One would expect that one would encounter evidence that one's conclusions from one's assumptions were wrong and so reject them and the original assumption and although that may occur in some cases, one may fall into the trap of self confirming delusions. This trap as well as treatment of delusions is discussed on the Holding On To Beliefs Page.
This suggests that one false assumption might also give rise to a delusional belief system even among people who reason in a normal way. In the case of society, if we have a false assumption about another group, e.g. the Jews killed Jesus and tried to kill Muhammad that could lead to the development of a lot of paranoid delusional beliefs about Jews and in fact has.
Another theory of delusion are that there is a delusional continuum and that there is an error in evaluating probabilities of events. Peters et. al. made an exam that measures delusional thinking (The Peters Delusions Inventory or PDI) and tested it on "normals" and "deluded people". Although psychotic inpatients scored higher than normals there was considerable overlap (Peters E. Joseph S. and Garety P., Schizophrenia Bulletin 25(3): 553-576, 1999.) People with delusional disorder have been shown on the average to be more likely to jump to conclusions based on insufficent evidence than normal people although there is overlap (Philippa A. Garety and Daniel Freeman, Cognitive Approaches To Delusions: A Critical Review of Theories and Evidence, British Journal of Clinical Psychology, 38, 113-154 1999)
Table of Contents