This blog post will look at what hallucinations are, what causes them, and what can be do to help people who suffer from them. Normally, we are pretty good at identifying what’s real in the environment, but occasionally this processing is distorted, and people see things which aren’t there. This is a hallucination, and the most common type is auditory.


Although they are a symptom of schizophrenia, they can occur in people without the condition, and factors such as drug use, sleep or sensory deprivation or bereavement can make them more likely to occur.

It has been hypothesised that hallucinations are caused by an internal event being misattributed to an external source. For example, internal speech is thought to originate from something external, and so is experienced as hearing a voice. Evidence to support this comes from a study by McGuire et al (1993) who found increased blood flow to Broca’s area during auditory hallucinations – this is an area of the brain involved in language production.

This externalising bias is thought to be caused by impairments in self-monitoring, which means that sufferers do not identify the sense of effort or intention behind their actions. Evidence for this comes from studies such as one carried out by Johns et al (2001), which ask patients to speak words out loud into a microphone. The words are then played back to the individual, some distorted and some in another person’s voice. The patient then has to identify whether or not they spoke the word. This study found that patients with hallucinations were more likely than healthy controls to identify their speech as someone else’s.


One of the most successful ways to treat hallucinations is using cognitive therapy, which involves challenging people’s beliefs about their voices. At first this is done using a hypothetical contradiction, before progressing to directly questioning their beliefs.

A new form of therapy to treat hallucinations has recently been developed, and involves the use of technology. Leff et al (2013) helped patients develop an avatar which resembled the voice their hear, and the patient was encouraged to stand up to the voice. The therapist spoke as the voice, and gradually changed their responses so that the avatar was under the control of the patient. This technique was found to reduce hallucinations more than traditional methods.

However, most of the research has only focused on auditory hallucinations, whereas they can occur in any sensory modality. Therefore, more needs to be done to develop successful therapies for these other types of hallucinations.


Thanks for reading!



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!