Hallucination

What are Hallucinations?

Hallucinations of various types are the most common perceptual abnormalities seen in psychiatric patients. Hearing voices that are not really there, seeing forms that, in fact, do not exist, or experiencing a sensation of bugs crawling on one’s skin when one is not infested, are common examples of hallucinating.

A hallucination is often described as ‘a perception without an object’. Perception is the process of making sense of the physical information we receive from our five sensory modalities.

True hallucinations and pseudohallucinations Opens in new window are byproduct of false perceptions in which there is an internal perception without an external object; and usually have the following important characteristics:

• To the patient, the nature of a hallucination is exactly the same as a normal sensory experience — i.e. it appears real. Therefore, patients often have little insight into their abnormal experience.

• They are experienced as external sensations from any one of the five sensory modalities (hearing, vision, smell, taste, touch) and should be distinguished from ideas, thoughts, images or fantasies which originate in the patient’s own mind.
• They occur without an external stimulus and are not merely distortions of an existing physical stimulus (see illusions   Opens in new window).

As symptoms of major mental disorder, hallucinations are the most significant type of abnormal perception Opens in new window.

It is important to appreciate that the subjective experience of hallucination is that of experiencing a normal percept in that modality of sensation.

• A true hallucination will be perceived as being in external space, distinct from imagined images, outside conscious control, and as possessing relative permanence.
• A pseudohallucination   Opens in new window will lack one or all of these characteristics and be subjectively experienced as internal or in my head.

The only characteristic of true perceptions which true hallucinations lack is publicness; hallucinating patients may accept that their experiences are not shared by others around them in the same way as a normal sensory experience.

Description of Various Types of Hallucinations

Hallucinations are described according to the involved sensory modality.

1. Auditory hallucinations

Auditory hallucinations are the most common type of hallucinations seen in psychiatric patients. The patient may hear clear voices:

• communicating to the patient (in this case known as second person hallucination),
• talking among themselves about the patient (third person hallucination),
• commenting about the patient’s activities (running commentary type hallucinations),
• or instructing the patient (commanding hallucination).

2. Visual hallucinations

Visual hallucinations are less common than auditory hallucinations. They are associated with organic disorders of the brain and with drug and alcohol intoxication and withdrawal.

Visual hallucinations are very rarely seen in psychotic illness alone but are reported in association with dementias, cortical tumors, stimulant and hallucinogen ingestion, and, most commonly, in delirium tremens.

The visual hallucinations seen in delirium tremens are characteristically Lilliputian hallucinations Opens in new window of miniature animals or people.

Patients may see people, objects, or animals and sometimes as a complete scene like a movie (scenic hallucination). Their presence in the absence of auditory hallucination should raise suspicion of some organic brain disorder.

3. Olfactory and gustatory hallucinations

Olfactory and gustatory hallucinations involve smell and taste, respectively. These may be difficult to distinguish from each other in a wide range of mental disorders.

Olfactory hallucinations are seen in epileptic auras, in depressive illnesses (where the smell is described as unpleasant or repulsive to others), and in schizophrenia Opens in new window. They may also occur in association with a persistent delusion of malodourousness.

4. Hypnagogic/hypnopompic hallucinations

Hypnagogic/hypnopompic hallucinations are transient false perceptions which occur on falling asleep (hypnagogic) or on waking (hypnopompic).

They may have the characteristics of true or pseudohallucinations and are most commonly visual or auditory. While they are sometimes seen in narcolepsy Opens in new window and affective illnesses, they are not indicative of ill health and are frequently reported by healthy people.

5. Tactile hallucinations

These can be a superficial sensation over or under the skin (tactile or haptic hallucination) or a feeling of sensations like pressure, tearing or twisting in deep visceral organs (visceral hallucination).

6. Elemental hallucinations

Elemental hallucinations are the hallucinatory experience of simple sensory elements, such as flashes of light or unstructured noises. They are associated with organic states.

7. Extracampine hallucinations

These are those false perceptions where the hallucination is of an external object beyond the normal range of perception of the sensory organs.

8. Functional hallucinations

Functional hallucinations are hallucinations of any modality that are experienced simultaneously with a normal stimulus in that modality (e.g. a patient who only experiences auditory hallucinations when s/he hears the sound of the ward’s air conditioning).

9. Reflex hallucinations

Reflex hallucinations are hallucinations in one modality of sensation experienced after experiencing a normal stimulus in another modality of sensation.