What are Hallucinations?
A hallucination is sensory perception which is experienced in the absence of external stimulus. Hallucinations can be visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Person will see, hear, smell, taste or feel sensation of touch even when there is nothing to cause such. They can occur as a result of:
- Substance abuse
- In mental illness such as schizophrenia
- In neurological condition such as Alzheimer’s disease
- Sleep deprivation
- Delirium tremens
- Charles Bonnet syndrome
- Drug-induced hallucination
- Sensory deprivation hallucination
They are different from other phenomena like:
- Dreaming in which person is sleeping
- Illusion in which there is distortion of real perception
- Imagery which is under voluntary control
- Pseudohallucination which does not mimic real perception
- Delusional perceptions in which real perception is given some additional and wrong significance.
Hallucinations may be manifested in a variety of forms
- Visual – A visual hallucination is perception of some external visual stimulus where there is none. Visual hallucinations are of two types, simple and complex.
- Simple visual hallucinations (SVH) also called non-formed visual hallucinations and elementary visual hallucinations. These refer to lights, colors, geometric shapes, and indiscrete objects. These are subdivided into SVH without structure and SVH with geometric structures.
- Complex visual hallucinations (CVH) also called formed visual hallucinations. CVH are clear images which are lifelike for example people, animals, objects, etc.
- Auditory – Auditory hallucinations are the perception of sound without outside stimulus. Auditory hallucinations are the most common type of hallucination. Auditory hallucinations are of two types: elementary and complex.
- Elementary hallucinations are the perception of sounds such as hissing, whistling, crackling etc.
- Complex hallucinations are voices, music or other sounds. These may be clear or not clear, may be familiar or unfamiliar, friendly or aggressive, without purpose beneficial or harmful, suggestive neutral or commanding.
- Olfactory – In this person is smelling odors that are not really present. This is also called phantosmia. Odors can be pleasant or unpleasant. Common pleasant are odors of perfumes, flowers etc. Common unpleasant are rotten flash, vomit, stool etc. This is different from parosmia in which smell is present but is perceived differently. In some serious cases, person experience smelling colors.
- Tactile – Tactile hallucinations are of sensory perception simulating various types of touch or pressure to the skin or other organs. These can be pleasant or unpleasant. One type of tactile hallucination is formication in which there is sensation of ants or insects crawling on or underneath the skin.
- Gustatory – Gustatory hallucination is the perception of taste without a stimulus. These hallucinations can be pleasant or unpleasant.
Other hallucinations can be :
- Proprioceptive – Person feels body is twisted or strangely positioned.
- Equilibrioceptive – Person feels out of balance
- Nociceptive – Person feels pain or being hurt
- Thermoceptive – Person feels sensation of heat and cold
- Chronoceptive – Person has distorted perception of time and period