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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Vindhya BellamKonda, M.B.B.S [2]
Hallucinations are defined as sensory perception in the absence of external stimuli. They are different from illusions, or perceptual distortions, which are the misconception of external stimuli.[1] Hallucinations may occur in any of the five senses and take on almost any form, which may include simple sensations (such as lights, colors, tastes, and smells) to more meaningful experiences such as seeing and interacting with fully formed animals and people, hearing voices and complex tactile sensations.
Auditory hallucinations, particularly the experience of hearing voices, are a common and often prominent feature of psychosis. Hallucinated voices may talk about, or to the person, and may involve several speakers with distinct personas. Auditory hallucinations tend to be particularly distressing when they are derogatory, commanding or preoccupying. However, the experience of hearing voices need not always be a negative one. Research has shown that the majority of people who hear voices are not in need of psychiatric help.[2] The Hearing Voices Movement has subsequently been created to support voice hearers, regardless of whether they are considered to have a mental illness or not.
Psychosis may involve delusional or paranoid beliefs. Karl Jaspers classified psychotic delusions into primary and secondary types. Primary delusions are defined as arising out of the blue and not being comprehensible in terms of normal mental processes, whereas secondary delusions may be understood as being influenced by the person's background or current situation (e.g., ethnic or sexual discrimination, religious beliefs, superstitious belief).[3]
Formal thought disorder describes an underlying disturbance to conscious thought and is classified largely by its effects on speech and writing. Affected persons may show pressure of speech (speaking incessantly and quickly), derailment or flight of ideas (switching topic mid-sentence or inappropriately), thought blocking, and rhyming or punning.
One important and puzzling feature of psychosis is usually an accompanying lack of insight into the unusual, strange, or bizarre nature of the person's experience or behaviour.[4] Even in the case of an acute psychosis, people may be completely unaware that their vivid hallucinations and impossible delusions are in any way unrealistic. This is not an absolute, however; insight can vary between individuals and throughout the duration of the psychotic episode.
It was previously believed that lack of insight was related to general cognitive dysfunction[5] or to avoidant coping style.[6] Later studies have found no statistical relationship between insight and cognitive function, either in groups of people who only have schizophrenia,[7] or in groups of psychotic people from various diagnostic categories.[8]
In some cases, particularly with auditory and visual hallucinations, the person experiencing the hallucinations has good insight, which may make the psychotic experience even more terrifying because the person realizes that he or she should not be hearing voices, but is.
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