a stimulus from a perceived object is combined with a mental image to produce a false perception. They often occur in normal people. For example the normal person walking on lonely road in the dark may get frightened; he may see the shadows of the trees and interprets them as threatening people. Illusions could also occur in psychiatric illness for example severe depression, acute confusional and others.
Hallucinations
This Is a false perception; the perception occurs in the absence of an external stimulus. This appears in the patient's external objective space (that is seems to be situated outside the patient) and is clearly defined. Hallucinations are described as being independent of the person's will, i.e. they cannot be voluntarily recalled or changed.
Hallucinations can occur of the different sense modalities:
- Auditory hallucinations
- Visual hallucinations
- Olfactory hallucinations
- Gustatory hallucinations
- Tactile hallucinations
Auditory hallucinations are common. They could occur in normal people(for example when falling sleep/wakeing up). In patients they could be simple hallucinations (noises, catches of song) or complex(voices talking, arguing). Complex hallucinations can be further divided:
- Second person auditory hallucinations - the patient hears a voice talking to him. This is common, and could occur in mood disorders with the psychotic features or schizophrenia.
- Third person auditory hallucinations - the patient hears several voices, talking about him (among themselves). This type of hallucinations is usually but not always seen in schizophrenia.
Prominent visual hallucinations are often more commonly seen in organic disorders such as acute alcohol withdrawal, acute confusional state, certain types of dementias. Although visual hallucinations could occur in psychiatric disorders per sae, prominent visual hallucinations should always raise the suspicion of an underlying organic pathology.
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