the cognitive psychology of delusions: a review

APPLIED COGNITIVE PSYCHOLOGY, VOL. 10,487-502 (1996)

The Cognitive Psychology of Delusions: A Review

EDGAR MILLER and POLYXENI KARONI University of Leicester, UK

SUMMARY Delusions have for a long time been regarded as one of the major signs of mental disorder. Above all else they are cognitive phenomena in that they purport to express ideas about the world or the self. Despite this it is only relatively recently that the ideas and methods of cognitive psychology have been used in the study of delusions, at least in any systematic way. This paper reviews the work carried out so far, which is starting to yield some consistent trends. These include an excessively self-seeking bias in judgments made by people with delusions and a tendency to make judgments on the basis of rather less evidence than controls.

INTRODUCTION

Delusions have long been regarded as one of the major symptoms of mental disorder. They are most commonly defined as ‘false beliefs’. A more detailed current definition is provided by the American Psychiatric Association (1994) in the fourth edition of its Diagnostic and Statistical Manual (DSM IV):

‘A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person’s culture or subculture (e.g. it is not an article of religious faith).’

According to this definition delusions are beliefs that have two key characteristics. They are clearly false or, at least, lie right outside the belief systems of others within the same culture or subculture and they are highly resistant to change even when faced with strong evidence to the contrary.

Whilst DSM IV offers a definition of delusions that is very much in line with the majority view, such a definition is not beyond criticism and alternatives exist (see Garety and Hemsley, 1994). One significant issue is whether delusions can be properly regarded as beliefs. For example, Berrios (1991) argues that delusions do not share some of the features of ordinary beliefs and are not therefore beliefs that happen to be patently false. His alternative definition is that delusions are ‘speech

Address for correspondence: Edgar Miller, Department of Psychology (Clinical Section), University of Leicester, Leicester LE1 7RH, UK.

CCC 08884080/96/060487-16 0 1996 by John Wiley & Sons, Ltd.

Received 24 February 1995 Accepted 16 February 1996

488 E. Miller and P . Karoni

acts, unwarranted in logic and/or in reality, purporting to carry information about the world or the self (Berrios, 1992). Space does not permit the conceptual issues concerning delusions to be properly explored. Despite significant reservations, the common definition of delusions remains that of ‘false beliefs’. The term ‘belief will be retained in this paper for convenience but without any necessary commitment to the notion that delusory ‘beliefs’ are similar in nature to ordinary, everyday beliefs.

Whether or not delusions do constitute ‘false beliefs’ or are better conceptualised in other ways, they are phenomena that reflect cognitive processes, in that they purport to represent ideas or notions that deluded people have about the world or themselves. It then becomes appropriate to ask by what cognitive processes delusions arise, and why, once established, are delusions apparently so resistant to change? This is especially so because the outcomes often implied by delusions, such as paranoid delusions, almost always fail to materialise.

Until recently little had been done to explore delusions from the standpoint of cognitive psychology although the situation is now changing. The aim of this paper is to describe the work that has been reported and to suggest a number of lines of enquiry that might lead to a better understanding of delusions in terms of how they might arise and the factors that maintain them.

This paper will first discuss a number of background issues that arise in considering delusions in the way proposed. Secondly, the question of reliability in the identification of delusions will be considered. This is followed by discussions of factors that may relate to the creation and maintenance of delusional beliefs.

Background issues

Before looking at delusions in greater detail a number of background points need to be made. In thinking about psychopathology, delusions are probably most closely associated with schizophrenia, and especially paranoid schizophrenia. This, of course, raises the question as to the extent to which diagnostic labels, like schizophrenia or depression, really do identify separable syndromes (see Bentall 1990; Costello, 1993). The position taken on this issue in the present paper is that of agnosticism, and all that is meant by reference to ‘schizophrenia’ is people exhibiting such features as to make them likely to be labelled as ‘schizophrenic’ within the psychiatric services. The important point that has to be kept in mind is that delusions can arise in a number of other alleged conditions such as depression and some organic disorders.

In this paper delusions are considered as a separate sign or symptom of psychological disturbance arising in the so-called ‘functional’ psychiatric disorders, since the relevant work is concerned with delusions, in schizophrenia. It remains to be determined whether the cognitive aspects of delusions will differ across the different kinds of clinical conditions within which delusions arise.

In dealing with an area like this it is also useful to be clear about possible cause and effect relationships. Most of the research so far links the presence of delusions to certain distortions in thinking or the making of attributions. It may be that delusions arise because of the presence of distortions in processes underlying the making of attributions and drawing of inferences. On the other hand, it could also be the case that the processes that cause delusions to appear also independently produce distortions in reasoning or attribution of the kind that have been studied.

Delusions: A Review 489

Cross-sectional studies of the kind that have been reported so far and that merely explore whether certain cognitive distortions can be demonstrated in subjects who are deluded cannot be used as strong evidence of a cause and effect relationship. Demonstrating cause and effect would require longitudinal investigations to determine whether cognitive distortions actually precede the occurrence of delusions rather than merely appearing hand-in-hand with them.

It has been common in discussions of delusions in classic psychopathology to distinguish between different types of delusions on phenomenological grounds. Space does not permit a full discussion of the various types of delusions that have been proposed, but a common distinction has been in terms of primary or secondary delusions (e.g. Jaspers, 1913). A primary delusion is one that arises without any discernible precipitating factor. The delusional idea@) appears to emerge de novo into the patient’s mind. In contrast, a secondary delusion is a manifestation of delusional thinking that is linked to some particular precipitating factor. For example, a person who is already predisposed to the notion that there are people around who might wish ill of him or her and who then becomes ill after a meal in the factory canteen, may decide that colleagues are trying to poison him or her.

Whilst the distinction between primary and secondary delusions may make some sense phenomenologically, it does raise difficulties. To claim that primary delusions just arise out of nowhere in the patient’s mind tends to put them beyond the range of experimental investigation. Secondly, the distinction may at least partially reflect the degree of specificity in delusional thinking. It is much easier to see a possible precipitant factor in the case of a belief that others are trying to poison the person than of a more general belief that the individual is the target of vaguely defined malevolent influences. For this reason, the distinction between primary and secondary delusions will not be made in this paper.

Other distinctions between alleged different types of delusions have been made (see Winters and Neale, 1983), often on the basis of content (e.g. paranoid delusions as opposed to delusions of grandeur). There is no evidence so far that any putative distortions in reasoning that might be associated with delusions will differ according to delusional content. In addition, cognitive research to date has concentrated on paranoid delusions, presumably because these are the most common and distinguishing between delusions on the basis of content has no real relevance for present purposes.

A final background issue concerns whether delusions are, as is implied in much classical psychopathology, discrete entities that are either present or absent. The alternative view is to regard them as dimensional, involving ‘a continuous distribution from the normal to the pathological’ (Garety and Hemsley, 1994). It is certainly the case that some empirical studies have suggested that the continuity view is more realistic (e.g. Strauss, 1969) as have treatment studies (e.g. Chadwick and Lowe, 1990), which showed changes in delusional intensity in response to psychological treatment.

Reliability of identification

A question that continually arises in any analysis of psychopathological phenomena is the reliability with which they can be identified. A lack of reliability in the diagnosis of alledged syndromes like schizophrenia has been a major plank in the


argument that it is inappropriate to use such syndromes as a focus of research (e.g. Bentall, 1990; Boyle, 1990; Costello, 1993). Whilst recent work on psychiatric diagnosis has undoubtedly enhanced reliability, as is conceded by some critics of the use of syndromes such as Costello (1993), it also has to be remembered that reliability does not guarantee validity.

A suggested way round this problem of the validity of syndromes is to change the focus away from syndromes to more specific signs and symptoms (Bentall, 1990; Costello, 1993). Unfortunately this just changes the locus of the very same problems. If it is not possible to identify consistently those who exhibit delusions from those who do not then it is difficult to maintain that what is being investigated is a real characteristic of patients.

Evidence relating to the reliability with which delusions can be identified is sparse. Kreitman, Sainsbury, Morrissey, Towers and Scrivener (1961) provided some data on the reliability with which certain common psychiatric symptoms, including delusions, could be identified. The level of inter-rater agreement was low at only 27% but the method of calculation did not take into account the small proportion of deluded subjects and the substantial agreement as to who did not exhibit delusions.

Fortunately, later studies have used more appropriate reliability coefficients. Wing, Birley, Cooper, Graham and Isaacs (1 967) obtained reliability coefficients (weighted kappas) ranging between 0.77 and 0.94 for the identification of delusions of different kinds. The higher figure of 0.94 refers to persecutory delusions, which have been the most commonly studied. Endicott and Spitzer (1978) reported even higher coefficients of 0.91 and over for assessing the presence of hallucinations and/ or delusions. In another study, which also involved the examination of inter-rater reliability for symptoms (Murphy et al. (1995)), a reliability coefficient for delusions of 0.76 was obtained. This is acceptable, if lower than the figures reported by Endicott and Spitzer (1978) and Wing et al. (1967).

It appears that the identification of delusions can be achieved at a sufficiently reliable level. This is especially so if carefully designed diagnostic schedules are used. However, descriptions of the methodology employed do not suggest that delusions have always been identified as rigorously in many of the papers referred to in the rest of this review.

Possible cognitive factors underlying delusions

Whatever their ultimate cause, delusions involve what would be regarded as aberrations of thinking. In fact the DSM IV definition cited above with its statement that delusions are ‘based on incorrect inference about external reality’ implies that distorted cognitive processes must be involved. It must then be asked, how do the abnormal thoughts or beliefs arise and why are they maintained? The rest of this paper goes on to examine delusions in the light of contemporary cognitive psychology. This is both in terms of describing what has been reported so far in the way of applying cognitive psychology to understanding delusions, as well as by suggesting other ways in which cognitive psychology might contribute to the further understanding and explaining of delusional phenomena.

Before further considering an approach from the standpoint of cognitive psychology, it needs to be mentioned that other psychological approaches to the understanding of delusions have been advocated (see Colby, 1977; Roberts, 1992;


Winters and Neale, 1983). In particular there are various psychodynamic hypotheses as to how delusions arise. The classic Freudian position is that paranoid delusions arise out of unconscious and repressed homosexual urges (Freud, 1915). This basic paychoanalytic hypothesis has proved unsatisfactory and at variance with empirical observations (e.g. Colby, 1977). Alternative psychodynamic formulations have been developed and are described elsewhere (e.g. Federn, 1952; Hingley, 1992). It is not intended to deal further with psychodynamic or other models unrelated to cognitive psychology in this paper.

COGNITIVE MODELS

Disturbed cognitive processes, especially thought disorder, have long been an alleged central feature of schizophrenia. There is a vast literature on cognitive abnormalities in schizophrenia that is far too extensive to consider here (for a recent review see Marengo, Harrow and Ednell, 1993). This paper is solely concerned with cognitive approaches linking faulty reasoning to delusional ideation and does not attempt to review work that falls outside this framework.

Delusions as anomalous sensory experiences

It is appropriate to begin with the one model of delusional thinking in schizophrenia that explicitly denies that abnormal reasoning processes have any role to play in the creation of delusions. In a series of papers, Maher argued that delusions arise from anomalous experiences such as hallucinations (e.g. Maher, 1974, 1988; Maher and Ross, 1984; Maher and Spitzer, 1993). The crux of Maher’s argument is that, on being faced with anomalous experiences, the individual has to find some reason for them. By using normal reasoning processes s/he ends up with an explanation that others regard as delusional.

This general model of delusions is not unique to Maher and his colleagues. For example, Frith (1979) suggested that those who exhibit delusions may suffer from a flood of additional material into consciousness, which is explained by normal reasoning processes and so results in delusions.

In support of his model, Maher (e.g. Maher and Spitzer, 1993) draws on a large body of work that implies that schizophrenic subjects suffer from abnormalities in attention and the early processing of incoming information (e.g. Magaro, 1980). Similarly there is some evidence that delusions can be associated with sensory defects, particularly deafness in older people (e.g. Almeida, Howard, Levy and David, 1995; Cooper and Curry, 1976; Cooper and Porter, 1976). Sensory impairments could then be associated with anomalous sensory experiences, in the sense of a misperception as opposed to a degraded sensory input alone. Furthermore, Maher has consistently claimed that there is little or no evidence that reasoning processes are disturbed in delusional patients.

If correct, this model means that seeking an understanding of delusions through abnormalities in reasoning or inference is misguided and evidence of malfunctioning perceptual processes should be sought. However, it can be argued that Maher’s model is far from well established and that, at the very least, it would be premature to foreclose on any approach to understanding delusions based on abnormal or biased reasoning processes.

492 E. Miller and P. Karoni

In the first place, whilst claims that delusions in the elderly are associated with sensory handicaps, especially deafness, are consistent with Maher’s views, it has to be pointed out that not all investigators have found such a link (e.g. Moore, 1981). Where this relationship arises, it is not the case that all subjects with delusions have sensory impairments. In the study by Almeida et al. (1995), 17% of a group with late paraphrenia used hearing aids as opposed to 6.1 YO of the controls, suggesting that deafness, although a risk factor, is not strongly linked to delusions in old people.

Secondly, Maher’s claims that biases or disturbances in reasoning processes have failed to be demonstrated in delusional patients are also very much open to question. In early papers on delusions (e.g. Maher, 1974), some alleged failures to find peculiarities of reasoning in schizophrenics are cited. Von Domarus (1994), on the basis of a clinical study, suggested that schizophrenics were prone to make a particular type of error in syllogistic reasoning. Subsequent investigations claim to have found no evidence of errors in syllogistic reasoning in schizophrenics (Gottesman and Chapman, 1960; Williams, 1964).

Several problems arise in accepting this evidence at face value. In the first place, subsequent evidence (e.g. Garety, Hemsley and Wesseley, 1991; Huq, Garety and Hemsley, 1988) can be considered as demonstrating biases in reasoning and this work is considered in greater detail below. The Gottesman and Chapman (1960) and Williams (1964) investigations were carried out on schizophrenics in general, and not specifically on schizophrenics with delusions. This is an important point given that it is debatable whether schizophrenia is a unitary entity. Finally, whilst Gottesman and Chapman (1 960) failed to find evidence of an increase in the kind of errors suggested by von Domarus (1944), they did not present their full data nor did they offer a complete analysis of the data that they did present. The data in one of their tables present the various types of response for a type of syllogism that was considered critical for the theory that they were concerned to evaluate. These data were not subject to any form of statistical analysis. When this is done by means of a chi-square test, a significantly different pattern of responses between the schizophrenic and control groups is apparent, although not in the way that was predicted. Therefore the study does offer some evidence indicating that schizophrenic reasoning may not be entirely normal.

A claimed feature of delusions, as in the definition of delusions given at the start of this paper (American Psychiatric Association, 1994), is that delusional ideas or beliefs are unusually resistant to change. If this is true, it is not a feature of delusions that can be explained on the basis of the anomalous experiences model as it has been presented so far. Maher’s argument on this point was that it has been erroneous to regard delusional beliefs as being unusually resistant to change or counterargument. Normal people can hold to beliefs very strongly and despite good arguments to the contrary. Normal and delusional beliefs, therefore, do not differ in this respect. This is a point that is open to empirical test but so far there appears to have been no attempt to do so.

There are other difficulties in the way of the anomalous experiences model of delusions. It does not appear to allow for the fact that there is empirical work suggesting that the nature of what is perceived may be influenced by certain cognitive processes, such as expectations (e.g. Gregory, 1980). Expectations or hypotheses that influence perception could then have their basis in anomalous reasoning processes. In passing, it can be noted that there are also possible


philosophical objections. The idea of an anomalous experience just arising in consciousness, which then has to be explained, by either rational or irrational means, smacks of what Dennett (1991) called the ‘Cartesian theatre’ (i.e. the notion that images or sensations arise at a single, definite point in time rather like pictures on the cinema screen of consciousness). Although this is a view that has considerable intuitive appeal, Dennett saw it as a manifestation of dualism and presented strong arguments as to its inherent implausibility. The philosophical arguments are too complex to be conveniently summarised here but the interested reader is referred to Dennett ( 199 1).

What can be concluded from this model, which sees delusions as essentially the attempt of a normal reasoning process to make sense of anomalous experiences? The suggestion that anomalous sensory experiences or perceptions may help to precipitate delusions is not unreasonable and is consistent with some evidence. What is less convincing and much more difficult to sustain, especially in view of the work considered in the following sections of this paper, is the claim that biased or disturbed reasoning processes play no part and that reasoning is essentially normal in those who exhibit delusions. It is the possible relationship between delusions and such things as disturbed reasoning or attributional processes that this paper now examines.

Distorted attributions

One possibility is that delusions may be linked to distorted attributional processes. Attributions, as studied by social psychologists (e.g. Fiske and Taylor, 1991), are a form of cognitive process whereby judgments are made or reached about the actions of others. Faced with given information, those prone to develop delusions may make unusual attributions, at least under some circumstances.

Bentall and his colleagues explored the attributions made by subjects with delusions in terms of social attribution theory, and particularly in terms of Kelley’s (1967) model of social attribution. As Bentall, Kaney and Dewey (1991) pointed out, social attribution theory may be an appropriate perspective, since many of the delusions shown by psychotic patients have strong social connotations (e.g. persecutory delusions).

Kaney and Bentall (1989) used subjects with persecutory delusions and depressive controls, asking them to make attributions relating to vignettes in the Attributional Style Questionnaire (Peterson, Semmel, Von Baeyer, Abramson, Metalsky and Seligman, 1982). The depressed and deluded subjects were similar in the extent to which they made strongly global and stable attributions for significant events. In this context an attribution by the subject indicating that, say, a positive outcome was due to the individual’s own skill would be considered ‘global’ if the implication was that the subject would be similarly skilful in other problem settings and ‘stable’ if this skilfulness were going to persist over time.

As compared to the depressive controls, subjects with persecutory delusions were much more prone to make external attributions for negatively valued events and more internal attributions for positively valued events. Here an ‘internal’ attribution is one that places the cause of the event within the individual, as when a positive outcome is viewed as the consequence of the individual’s own capabilities, as opposed to an ‘external’ attribution, which would imply that the outcome was due to


extraneous factors or mere chance. Substantially similar results to those of Kaney and Bentall (1989) were also described by Candido and Romney (1990). However, Silverman and Peterson (1993), whilst confirming a tendency for paranoid subjects to make more internal attributions for positive events, found that these same subjects also give more internal attributions for negative events.

Whilst these investigations show differences in attributional style between the two groups, they do not indicate whether either or both could be considered abnormal in terms of their attributional styles. Nevertheless an undue tendency to make external attributions for negative and internal attributions for positive events would fit with the occurrence of both persecutory and grandiose delusions (i.e. bad things occur because of the actions of others and good things are very much down to me).

A follow-up to the Kaney and Bentall (1989) report was provided by Kinderman, Kaney, Morley and Bentall (1992). This report extends the size of the Kaney and Bentall (1989) samples, as well as carrying out further analyses based on subjects rating the causes of events that they themselves had generated. The tendency for deluded subjects to show a ‘self-serving’ bias in their attributions was confirmed in that the subjects themselves regarded their own causal attributions as being biased towards internality for positive events and to externality for negative events. On the other hand, when independent judges were asked to rate the causes given by subjects, then deluded, normal and depressed subjects were seen as showing no differences in internality. As the authors express it, it appears that the differences shown by deluded subjects might be related more towards the attributions they make about their attributions.

Kelley’s (1967) theory of social attribution suggests that three types of information, relating to distinctiveness, consistency and consensus, are of importance in determining social attributions. Thus the basic situation in which ‘David hits John’ will be seen as due to some characteristic of John (i.e. a stimulus attribution in terms of the theory) if the action is distinctive to John (David does not hit other people), is consistent with the same actor’s previous behaviour to the individual (this is not the first time David has hit John) and there is consensus (John is frequently hit by other people). If there is low distinctiveness, consistency and consensus then the cause would be attributed to the person carrying out the actions or to the circumstances under which the events occurred (person attributions or circumstance attributions in the terms of the theory).

Bentall et al. (1991) used the Social Attributions Questionnaire based on a report by McArthur (1972). This has a set of vignettes describing interactions between two people. The actions could be either positively or negatively valued and information relating to the interactions was also provided, of a kind linked to Kelley’s concepts of distinctiveness, consistency and consensus. Subjects with persecutory delusions, as well as both depressed and normal controls, were required to choose between alternative attributions reflecting person, circumstance and stimulus attributions for the events described. Those with persecutory delusions were found to make excessive person attributions for negative events (i.e. in the very simple example of ‘David hits John’ then David is more likely to be blamed).

An interesting additional point is that the deluded subjects also expressed higher levels of certainty in the accuracy of their judgments. This is consistent with reports by Huq et al. (1988) and Garety et al. (1991) based on a very different type of experimental task, which also showed deluded subjects to be unusually confident in their judgments as compared to controls.


In yet a further study of attributions in deluded subjects, Lyon, Kaney and Bentall (1 994) followed up the tendency to produce ‘self-serving’ biases in attributions, whereby positive outcomes receive internal and negative outcomes receive external attributions. Based on Zigler and Glick’s (1988) hypothesis that paranoia may be a camouflaged form of depression, they argued that the ‘self-serving’ bias operates to reduce or allay depressive feelings. If this is so the bias would operate strongly when using transparent or obvious tests of attributional style but would be much less likely to occur with opaque or non-obvious tests. Again subjects, who consisted both of patients with paranoid delusions together with depressed and normal controls, were asked to make judgments or attributions relating to the outcome of situations described in short vignettes. The normal and depressed subjects showed similar patterns of attribution regardless of whether the vignettes were designed to provide a transparent or an opaque test. In contrast, subjects with paranoid delusions showed a change in that, as predicted, they were more likely to offer an external attribution in explaining a negative outcome with transparent test items. With opaque test items their attributions were rather more like those of the other two groups.

Information processing biases

One possibility in terms of understanding delusions is that deluded individuals are especially sensitive to, or are selectively biased in, processing information of certain kinds. Bentall and Kaney (1989) adapted the Stroop test to include words with a paranoid content. Such words created greater interference in the task of naming the colour of the ink in which the words had been written than other kinds of words for subjects with persecutory delusions.

In a further experiment, Kaney, Wolfenden, Dewey and Bentall (1992) required subjects to recall vignettes with either threatening or neutral themes. Subjects with delusions recalled more threatening propositions than depressed controls. This bias in memory tasks was confirmed by Bentall (1994) who asked subjects to recall words that were threat-related, depression-related or neutral. As compared to normal controls, the deluded group were more prone to recall both threat- and depression-related words where as a depressed group showed a bias towards depression-related words only.

Taken together these two investigations support the notion that sufferers from paranoid delusions are biased to process information of a threatening or persecutory nature more readily than non-deluded control subjects. They may also have a bias to depression-related material. Whether this is a cause or a consequence of being deluded is not clear from the work so far.

Nusory correlations

One well-established phenomenon in normal subjects is that of ‘illusory correlations’ (Chapman, 1967; Plous, 1993). Illusory correlations occur when, for example, subjects are exposed to a sequence of pairs of words where the words making the different pairs are linked at random. After exposure, subjects then judge pairs that carry associative connections (e.g. ‘table-chair’) as having occurred in the sequence more frequently than pairs with little or no associative connection (e.g. ‘house- anger’). This is despite the actual occurrence of these pairs within the observed sequence being exactly the same.


Brennan and Hemsley (1984) described an experiment of this kind using both paranoid and non-paranoid schizophrenics, as well as normal controls. All three groups showed a tendency to make illusory correlations but this was most marked in the paranoid schizophrenics and least evident in the non-paranoid patients. The strength of the effect in the normal controls was midway between that of the two schizophrenic groups. It is interesting that the two word pairs that most differentiated the groups were those most related to paranoid ideation (‘victim- killer’ and ‘secret-spy’). This study implies a tendency in the paranoid group to have increased sensitivity to associations of stimuli that might imply threat.

The use of Bayes’ theorem

Hemsley and Garety (1986) advocated the use of Bayesian theory as a normative model and the examination of judgmental processes in deluded subjects in terms of their departure from the idealised norm provided by this model. So far this has not been followed up to any great degree but they and their colleagues have reported two studies influenced by this approach.

Huq et al. (1988) and Garety et aZ. (1991) used a particular inferential reasoning task. Subjects are shown two containers each of which contains coloured beads. One container has pink and green beads in the ratio of 85 pink to 15 green. The other container has the same colours of beads but in the reverse proportion. As far as the subject is concerned, the two containers are placed out of sight and the experimenter then draws a sequence of beads from one container. As beads emerge, the subject has to indicate the point at which he/she feels able to make a judgment as to which container the beads are being drawn from and how certain or confident he/she is in this judgment.

In the initial experiment, Huq et al. (1988) compared deluded schizophrenics with a group of non-deluded, non-schizophrenic psychiatric patients and a normal control group. They found that the deluded schizophrenics required less information (i.e. the drawing of fewer beads from the container) before reaching a decision as to which container was involved, and they also expressed higher levels of certainty as to the correctness of their decisions than did either of the other groups. In a further, similar experiment (Garety et at. 1991), this general finding was confirmed with the further indication that, when given further disconfirmatory evidence, deluded schizophrenics were also more ready to change their estimates of the likelihood that something was the case. This additional finding is a little unexpected in view of the common clinical opinion that deluded ideas are held with unusual tenacity and resistance to change in the light of apparently disconfirmatory evidence.

Although not really within the framework of Bayesian inference, it is worth noting that John and Dodgson (1994) have provided a partial confirmation of Huq et aZ.’s (1988) findings using a rather different task. Deluded psychiatric patients, the vast majority of whom were also diagnosed as schizophrenics, together with a non-deluded psychiatric control group, as well as a normal control group, were asked to take part in a version of the ‘twenty questions’ game. Their deluded subjects, like those of Huq et al. requested less informtion (i.e. asked fewer questions) before making a decision. The tendency of deluded patients to jump to conclusions on the basis of lesser amounts of information than required by control groups, therefore appears to be a stable finding, which has appeared with the use of two very different experimental paradigms.


Contingency judgment

Kaney and Bentall (1992) used a contingency judgment task whereby subjects were presented with sets of two stimuli on a computer screen and had to select the ‘correct’ one. After each response subjects were informed whether the response was ‘right’ or ‘wrong’ and a cumulative score of the number of ‘correct’ responses was given. In fact the sequences were organised such that subjects were informed that their responses were ‘right’ or ‘wrong’ in a predetermined sequence that operated irrespective of their actual response choices. There were two separate test sequences with subjects eventually ending up with a high score on one and a rather low score on the other.

The key part of the investigation was then based on asking subjects to estimate the degree of control they thought that they had managed over winning and losing in each of the two test sequences. As compared to normal subjects and psychiatric controls, those with paranoid delusions rated themselves as having greater control over the sequence in which they got a high score. This confirms the self-serving bias found in the more conventional attributional studies described in a previous section.

Self monitoring

Frith suggested that schizophrenics may have a deficit in what he has described as ‘self-monitoring’ (e.g. Frith, 1992). There is a need for people to distinguish events caused by their own actions as opposed to those caused by external agents. If the schizophrenic is not aware of his/her own efforts to initiate thoughts or of the effort that goes into thoughts, then his/her own thoughts may be experienced as alien and attributed to external agencies. This model is most readily applied to hallucinations but Frith argued that such failures in self-monitoring could underlie at least some delusions. This is especially so for delusions of control where the patient feels that thoughts or actions are being determined by external forces.

There is some evidence to support this notion of poor self-monitoring in schizophrenics. Harvey (1 985) found that thought-disordered schizophrenics were later impaired in determining which words they had said out loud as opposed to those they had merely imagined. Similarly, Frith and Done (1989) used a finding that normal subjects carrying out a tracking task can often correct errors without any visual feedback, presumably because they have some internal monitoring system that tells them they have made an erroneous response. In a task of this nature, Frith and Done found that schizophrenic subjects corrected errors less frequently than controls where no visual feedback was provided.

Whilst there is evidence consistent with an impairment in self-monitoring in schizophrenics in general, appropriate studies have yet to be carried out using deluded subjects. It remains to be seen how this model would fare in relation to paranoid delusions where its application is rather less obvious than to delusions of control.

DISCUSSION

The attempt to understand delusions in terms of cognitive psychology has not, as yet, progressed far. Nevertheless some useful findings have emerged and what remains is to evaluate their significance.


There is now much evidence consistent with the proposition that delusions are associated with abnormalities or biases in reasoning and decision making. In addition to the work using cognitive models or approaches to understand or explain delusions, which form the main concern of this paper, there is some additional evidence from the use of cognitive therapy to treat delusions.

Whilst the therapeutic studies carried out so far do have significant limitations, there is at least some indication that cognitively based treatments may be of some value in reducing the intensity of delusional conviction (e.g. Brett-Jones, Garety and Hemsley, 1987; Chadwick and Lowe, 1990; Watts, Powell and Flustin, 1973). That therapies based on cognitive approaches have some therapeutic efficacy argues in favour of cognitive models of delusions, although it has to be acknowledged that there is no process research to indicate just how cognitively based interventions exert their effect.

The one major voice arguing against such a conclusion is that of Maher (e.g. Maher and Ross, 1984; Maher and Spitzer, 1993), who advocates the view that delusions arise from the use of essentially normal reasoning processes to make sense of anomalous experiences.

This position was discussed in some detail in an earlier section and was criticised on two major grounds. The first is that the perceptual processes that lead to experience do not themselves appear to be divorced from the influence of more central cognitive processes. Secondly, there is considerable evidence from the studies described in other sections of this paper to indicate that reasoning is disturbed in deluded subjects. This is certainly not to deny that anomalous experiences could contribute to the creation of delusions. What appears clear is that this model is becoming increasingly implausible as a sole explanation of delusions.

Having accepted that reasoning and decision making is disturbed or biased in people suffering from delusions, what can be concluded so far about the nature of this bias? In the first place, those with paranoid delusions show a selective bias in information processing towards persecutory or threat-related material, as demonstrated in studies using an adapted Stroop test or tests of recall of information (e.g. Kaney et al., 1992). Secondly, they appear to be quick to jump to conclusions in that they require less information to reach a judgment (e.g Huq et al., 1988; John and Dodgson, 1994). Also, the suggestion is that conclusions once reached are held with greater conviction. In addition, there is also evidence from several studies that people with delusions have a self-serving attributional bias. Positive outcomes are more likely to be regarded as being due to the individual’s own merits whereas responsibility for negative outcomes is more likely to be assigned to others. The impairment of self-monitoring proposed by Frith (1992) remains to be properly tested in relation to delusions.

So far these findings are relatively easy to link to the formation of delusions, at least in very general terms. It is hardly surprising that those with paranoid delusions should be selectively biased to threatening information or that they attribute negative outcomes to others. That they are also quicker to jump to conclusions, and form conclusions on the basis of less evidence, could also be linked to the formation of delusions. However, this is at a relatively low level of analysis and many questions remain to be resolved.

In the first place, as has already been pointed out, cause and effect relationships are not clear from this work. Do these cognitive biases lead to delusion formation or


are they produced in association with delusions by whatever process does lead to the formation of delusions? Possibly the most practical way of obtaining some leverage on this question would be to study patients with delusions close to the point of referral to the psychiatric services, when delusions are most strongly manifest, and again after their delusions have disappeared or at least been substantially reduced. If the cognitive biases persist after delusions have resolved then this implies that these biases are long-standing characteristics of people prone to develop delusions, and hence might have a causal role. If these biases disappear with the delusions then this is less likely to be the case and there may be other manifestations of the same problem that produces delusions.

As Bentall el al. (1991) pointed out, many delusions have strong social connotations, which makes work on attributional processes potentially of especial relevance. So far, the investigations concerned with attributions have largely involved taking work originally done with other groups (normal attributions or work with depression) and applying the same procedures to deluded subjects. This has given some leads, such as the abnormally strong self-serving bias. However, more precise questions need to be asked.

As examples of more precise questions that need to be asked, consider the suggestion that being both prone to jump to conclusions and having a self-seeking attributional bias can be linked to the formation of delusions. If something undesirable happens, the individual prone to develop paranoid delusions may well jump too readily to the conclusion that this is due to the actions of someone else, and from this it would follow that this other person is deliberately trying to exert some sort of malign influence. However, this needs to be taken further. Under exactly what circumstances are delusion-prone subjects most likely to jump to premature conclusions? Under what circumstances are these premature conclusions especially likely to involve the operation 0f.a malign influence as opposed to, say, just being accidental? Similarly, are there selective factors governing the sorts of people, or groups of people, who are presumed to be the instigators of the negative events?

Another possible question concerns the apparent imperviousness of delusional ideas or beliefs to change in the face of repeated failure to verify. Are delusional beliefs really unduly resistant to modification? Alternatively, is it that they are no different from all other beliefs held with considerable conviction, including those of normal subjects, in the degree to which they are highly impervious to contrary information or argument?

If the paranoid individual who appears to believe that some person or agency is trying to poison him, sustains this belief over a very long period in the face of no apparent poisoning incident, why is this so? Possibly a normal belief would be modified under such circumstances. It may be that the paranoid individuals have different notions as to what constitutes evidence for or against the delusional ideas that they hold. Alternatively, there is a bias in normal reasoning such that information contrary to a pre-existing notion or hypothesis is given less weight than equivalent information that is confirmatory (Plous, 1993). It could be that this bias is more extreme in those who develop delusions.

Whatever else they may also be, delusions are primarily cognitive phenomena. It is, therefore, highly appropriate that approaches to studying them based on cognitive psychology should be pursued. In line with this, some progress towards understanding cognitive processes associated with delusions is being made. Much


still remains to be done, but one major hope is that better understanding of the cognitive processes underlying delusions will lead to more effective forms of intervention.

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