Can you imagine constantly feeling as though people are plotting against you, or that they are watching you and spreading rumors? These are common symptoms of people who suffer from delusions, which is turn is a symptom of schizophrenia.

Delusions are defined as implausible, unfounded and strongly held beliefs which are personal to the individual and are extremely preoccupying and distressing to them (Freeman, 2007). There are 3 main types:

  1. Grandiose: beliefs that they have a special talent or are related to someone special
  2. Persecutory: beliefs that they are going to come to some harm which is intended by others
  3. Reference: beliefs that others are watching them or deliberately spreading ideas about them

One of the most influential models of delusions is the Threat-Evaluation Model (Freeman et al, 2002). This states that there are 3 main psychological processes which lead to uncertainty, and in turn to a delusion – shown in the flow chart below:

threat anticipation


The first of these processes is deficits in reasoning; in particular they jump to conclusions rather than considering all the evidence.

This has been shown by the Beads Task – participants are presented with 2 jars filled with 2 different coloured beads in opposite proportions e.g. 85 red, 15 blue in one; 15 red and 85 blue in the other.

The jars are then hidden from view, and the experimenter picks out beads from one of the jars one by one. The participants’ task is to work out which jar the beads are from. Several studies have found that schizophrenia patients need fewer draws to make a decision, compared to healthy participants, suggesting that they have a tendency to jump to conclusions.

The second of these processes is anomalous experiences – these are often internal and do not have an immediate explanation, so patients attribute them to external sources. For example, Zimbardo et al (1981) used hypnosis to induce a hearing problem in participants, with half told why, and half not. They found that the participants who were not told about their hearing problem had more paranoid thoughts during a social interaction.

The last process is emotions – depression and low self-esteem are thought to cause a negative bias when interpreting events, which can lead to delusions. Freeman et al (2003) showed this using a virtual reality study, in which participants had to go on a virtual tube journey. The avatars on the tube were programmed to behave neutrally, however 1/3 participants had persecutory thoughts about them, e.g. they looked intimidating. The researchers concluded that this is caused by higher levels of anxiety and interpersonal sensitivity.


I hope you liked this brief overview of this complex topic – check back soon for more posts!

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