Hallucination is False perception without any external stimulus which is not a sensory distortion or a misinterpretation & it occurs at the same time as real perception.


1. Emotions :

  • Very depressed patients with delusions of guilt may hear voices reproaching them.
  • These are not continuous voices (as in schizophrenia) but tend to be fragmentary, uttering single words or short phrases.

2. Suggestion :

  • Normal subjects can be persuaded to hallucinate either by hypnosis or by brief task motivating instructions.
  • When a group was asked to walk down dimly lit corridor & stop when they saw a faint light over the door at the end, most of the people stopped walking at the same time saying they could see a light even though there was no light source.

3. Disorder of a Peripheral Sense Organ:

• Auditory Hallucination may occur in Ear diseases & Visual Hallucinations in Eye diseases, but often there is some disorder of central nervous system as well.
Charles Bonnet Syndrome (Phantom visual images) is a condition in which complex visual hallucinations occur in the absence of any psychopathology. It is associated with either central or peripheral reduction in vision.

4. Sensory deprivation:

• If all incoming stimuli are reduced to a minimum in normal subjects, they will begin to hallucinate after a few hours.
e.g. deafness may cause paranoid disorder of deaf.

5. Disorder of CNS:

• Lesions of Diencephalons and Cortex may produce hallucinations. These are mostly visual but can be auditory.

Differential Diagnosis:

  1. Illusions
  2. Pseudohallucination: These are located in subjective space (for example, inside head) and not in objective space like true perception.
  3. Hypnogogic/Hypnopompic images
  4. Vivid imagery

Hallucinations of individual senses:

I. Auditory Hallucinations:

(A) Elementary Auditory Hallucinations:

  • Simple noises, bells and undifferentiated whispers or voices.
(B) Hallucinatory Voices:

Hallucinatory voices are characteristic of Schizophrenia. These can also occur in Mood disorders, Dementia or Delirium but are less well formed than those described in schizophrenia.

Patient may explain origin of voices in different ways. They may say that voices are the result of witchcraft, telepathy, radio, television etc. Sometimes, they claim that the voices come from within their bodies such as arms, legs, stomach etc.

Different types of auditory hallucinations can occur:

  1. Audible Thoughts: Hearing one’s thoughts spoken aloud.
  2. Thought Echo: Hearing one’s thoughts spoken after the thoughts have occurred.
  3. Imperative Hallucinations: Sometimes, auditory hallucinations give instructions to the patient, who may or may not act upon them.
  4. Running Commentary: Sometimes, voices talk about the person in the third person & may give a running commentary on their actions. These are among Schneider’s first-rank symptoms & once thought to be diagnostic of Schizophrenia.

Auditory hallucinations can be abusive, neutral or pleasant. Many patients have continuous hallucinations that do not trouble them . But some patients may stop all other activities & start listening & even replying to them.

II. Visual Hallucinations:

Visual hallucinations are more common in acute organic states with clouding of consciousness than in Psychiatric illness. So, visual hallucinations should raise a doubt before making a diagnosis of psychiatric illness.

Visual hallucinations can be flashes of light, partly organised in the form of patterns or completely organised in the form of visions of people, objects or animals.

  • All varieties of visual hallucinations are found in acute organic states.
  • Small animals & insects are seen most commonly in delirium.
  • Combined visual & auditory hallucinations may be seen in Temporal Lobe Epilepsy & Schizophrenia of late onset.
  • Lilliputian hallucinations involves seeing tiny people or objects. Unlike other hallucinations, these are accompanied by pleasure & amusement. These are seen commonly in delirium tremens.

III. Olfactory (Smell) Hallucinations:

Olfactory hallucinations can occur in Schizophrenia, Organic states & depressive psychosis.

e.g. Some schizophrenic patients say that they smell gas & that their enemies are poisoning them by pumping gas into the room

Sometimes, the smell may be pleasant. For example, some religious people can smell roses around certain saints (Padre Pio phenomenon).

IV. Gustatory (Taste) Hallucinations:

Hallucinations of taste occur in Schizophrenia & acute organic states.

V. Tactile (Touch) Hallucinations:

This is common in acute organic states. in the absence of coarse brain disease, the most likely diagnosis is schizophrenia.

  • Cocaine Bugs: In cocaine psychosis, patient may feel small insects crawling over the body.
  • Sexual hallucinations: Patient complain that she could feel penis of somebody in her vagina.

Sims (2003) classifies tactile hallucinations into 3 main types:

1. Superficial Tactile hallucinations:

It is further subdivided into:

  1. Thermic: e.g. a cold wind blowing across the face.
  2. Haptic: e.g. feeling a hand brushing against the skin.
  3. Hygric: feeling fluid such as water running from the head into the stomach.
  4. Paraesthetic: feeling pins & needles against the skin. These are seen most commonly in organic diseases.
2. Kinaesthetic Hallucinations:

These hallucinations affect muscles & joints. Patient feels that their limbs are being twisted, pulled or moved. Vestibular sensations (Sinking in bed or flying through the air) is a variant of kinaesthetic hallucinations & occur in delirium tremens and benzodiazepine withdrawal.

3.Visceral Hallucinations:

In this, patient complains that his/her organs are being torn out or the flesh ripped away from his/her body.


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