Delusions and Hallucinations

Psychology 101: The 101 Ideas, Concepts and Theories that Have Shaped Our World - Adrian Furnham 2021

Delusions and Hallucinations

Voices in my head. Chanting. Kisses. Bread. Prove Yourself. Fight. Shove. Learn. Earn. Look for love. (Vikram Seth, Voices, 1990)

Art thou not, fatal vision, sensible to feeling as to sight? Or thou but a dagger of the mind, a false creation, proceeding from the heat-oppressed brain? (Shakespeare, Macbeth)


It is important to make various distinctions between hallucinations, illusions and delusions. An illusion is a real reaction to a real sensation with a misattributed cause. A delusion is a belief held by an individual or a group that is demonstrably false, completely fanciful or more likely simply self-deceptive. Most importantly a delusion is impossible or patently untrue.

The most written about of all delusions, namely paranoia, has been shown to follow various stages: general suspiciousness, selective perception of others, hostility, paranoid ’illumination’ where all things fall into place and finally paradoxical delusions of influence and persecution.

Delusions often totally preoccupy people and cause them considerable distress. It should be noted that delusions are different from illusions. We have visionary and auditory illusions — for instance that the sun goes round the earth or that ventriloquists’ dummies actually speak. We have selective memories/illusions of happy childhoods. These are things that seem true to the senses or memory but are known to be false or have no basis in reality.


Psychiatrists may diagnose someone as having a delusion disorder under a number of very specific situations. First, a person must manifest one or more non-bizarre delusions for at least a month. Second, the person has not met other behavioural criteria for being classified as a person with schizophrenia. Third, audio and visual hallucinations are not prominent though tactile and olfactory hallucinations may be. Fourth, despite the delusions of their behavioural consequences a person’s psychosocial functioning is not essentially impaired such that they are not thought of as particularly odd or bizarre. Fifth, if the specific delusions have an impact on a person’s mood these mood changes do not last very long. Sixth, the disturbance is not the result of physiological or medical conditions (like the medication a person is on).

Psychiatrists have noticed five clear types of delusions:

Erotomanic: The main theme that they believe another person is seriously in love with them, more in the Hollywood romantic, even spiritual, way rather than in the sexual sense. It is often a famous person (film star, sporting hero) but also powerful superiors at work.

Grandiose: These are sometimes called delusions of grandeur and are manifest when a person believes (with no evidence) that they are special: they have amazing abilities or perspicacity or have really made a vitally important discovery.

Jealous: This is clearly manifest in the strong, but quite unfounded belief that a partner is unfaithful and cheating on them. Odd bits of ’evidence’ are put forward for these claims. They may hire a private detective, attempt to imprison their partner as well as physically and verbally attack them.

Persecutory: This is the belief that someone or some group are conspiring against them. They are cheating, spying on, harassing, gossiping about and even attempting to poison or drug you. They are often angry and resentful with deep feelings of injustice.

Somatic: This is the delusion that one’s own body is somehow strange or not functioning properly. It maybe the belief one smells odd or that particular parts (nose, breasts and feet) are particularly odd, misshapen or ugly.

In essence the causes are not known.


A hallucination is quite simply the perception of something — a noise, smell, sight — that is not there. Hallucinations involve sensing something while awake and conscious that is not actually physically present. It is sensation without stimulus.

A sensory hallucination may include hearing voices of long dead or mythical people, or it may be of insects crawling on, or under, the skin. It may be of angels or fairies dancing in bright lights. Some are highly idiosyncratic, many transient, unreal and bewildering.

Hallucinations are known to be associated with many things including sleep (particularly deprivation), certain drug use (the obviously termed hallucinogens), mental illness (particularly psychosis) and very specific neurological illnesses. Hallucinations occur often in schizophrenic episodes and are described in psychiatric manuals as ’a running commentary on the person and two or more voices conversing with each other’.

’Hearing voices’ is perhaps one of the most well-known ’signs of madness’. It is particularly associated with the psychotic disorders such as schizophrenia. People hear voices of specific or unidentifiable people when others present cannot hear them.

People have been reported seeing animals, innate objects and people not present. They may be ’ghosts’ or ’angels’ and some involve quite complicated scenes or bizarre situations. Some visual hallucinations are silent but in some people speak, often directly to the individual experiencing the hallucination giving them specific commands.


There are six causes of hallucinations.

The first is drugs, including alcohol and marijuana but also cocaine, heroin or LSD. The second is high fever, especially in young or old people. Third, they may occur in those with very specific sensory problems like blindness or deafness. People who go deaf often say they hear voices. Similarly these who have limbs amputated experience phantom limbs with all the movement, even pain, experienced.

Fourth, they occur in people with severe physical illnesses like brain cancer, kidney or liver failure. Fifth, they can and do occur if suffering from alcohol-related delirium tremors or later life dementia. Sixth, they are often closely associated with specific, severe, psychotic disorder like post-traumatic stress disorder and schizophrenia. Those who have experienced post-traumatic stress disorder often experience flashbacks. Thus when they hear certain sounds or detect certain smells they are instantly transformed back to times of trauma like war or accidents and have powerful flashback hallucinations of particular events. Also in times of great stress and mourning some people hear reassuring voices that calm the senses.


There are traditionally, sorts of psychological explanations for the occurrence of hallucinations. Freudians saw the hallucinations as projections of unconscious wishes or wants. The idea was that the person experiences as ’real’, something they felt, but could not express because it was below consciousness.

Cognitive psychologists point to problems in cognition processing, particularly metacognition which is concerned with your understanding of others’ understanding of events. That is hallucinations are misinterpreted of others’ behaviour.

However, it is the biological psychologists who are most clear about the causes. They see them primarily as deficits in brain states as a result of damage or chemical imbalances. Certainly they have been able to locate brain regions and identify pharmaceutical processes that lead to hallucinations.


American Psychiatric Association. (2015). Diagnostic and Statistical Manual of Mental Disorders (5th ed.) Washington, DC.

Oldham, J. & Morris, L. (1991). Personality Self-Portrait. New York: Bantam Books.