A hallucination in the broadest sense is a perception in the absence of a stimulus. In Psychology and the Cognitive sciences perception is the process of attaining awareness or understanding of sensory Information. In Physiology, a stimulus is a detectable change in the internal or external environment In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli and that have qualities of real perception in that they are vivid, substantial, and located in external objective space. These definitions distinguish hallucinations from the related phenomena of dreaming (no consciousness), illusion (distorted or misinterpreted real perception), imagery (does not mimick real perception and is under voluntary control), and pseudohallucination (does not mimick real perception, but is not under voluntary control). Dreams are the images sounds thoughts and feelings experienced while Sleeping, particularly strongly associated with Rapid eye movement sleep. An illusion is a distortion of the senses revealing how the Brain normally organizes and interprets sensory stimulation Vagina Imagery is used in literature to refer to descriptive language that evokes sensory experience ^[1] Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted genuine perception is given some additional (and typically bizarre) significance.

Hallucinations may occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, and thermoceptive. The visual system is the part of the Nervous system which allows organisms to see. The auditory system is the Sensory system for the sense of hearing. Olfaction (also known as olfactics or smell) refers to the Sense of smell. Taste (or more formally gustation) is a form of direct Chemoreception and is one of the traditional five Senses Proprioception (ˌproʊpriːəˈsɛpʃən PRO -pree-o-SEP-shun from Latin proprius, meaning "one's own" and perception is the Sense Equilibrioception or sense of balance is one of the physiological Senses It helps prevent Humans and Animals from falling over when Nociception (synonym nociperception is defined as "the neural processes of encoding and processing Noxious stimuli. Thermoception or thermoreception is the Sense by which an Organism perceives Temperature.

A mild form of hallucination is known as a disturbance, and can occur in any of the senses above. These may be things like seeing movement in peripheral vision, or hearing faint noises and voices. Peripheral vision is a part of vision that occurs outside the very center of gaze

Hypnagogic hallucinations and hypnopompic hallucinations are considered normal phenomena. Hypnagogia ( Greek ὕπνος húpnos "sleep" + the root found in ἄγω ágō "to lead away conduct convey" ἀγωγεύς A hypnopompic state (or hypnopomp) is the state of consciousness leading out of sleep a term coined by the spiritualist Frederick Myers Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Hallucinations may also be associated with drug use (particularly deliriants), sleep deprivation, psychosis, neurological disorders, and delirium tremens. A psychoactive drug or psychotropic substance is a Chemical substance that acts primarily upon the Central nervous system where it alters Brain The deliriants (or Anticholinergics are a special class of acetylcholine -inhibitor Dissociatives The name comes from their primary effect of inducing Sleep deprivation is a general lack of the necessary amount of Sleep. Psychosis (from the Greek ψυχή "psyche" for mind or soul and -οσις "-osis" for abnormal condition with adjective psychotic Delirium tremens (colloquially the DTs, " the horrors " " the fear "" the shakes "" jazz hands ""

Contents 1 Prevalence 2 Auditory hallucinations 2.1 Hypnagogic hallucination 2.2 Peduncular hallucinosis 2.3 Delirium tremens 2.4 Parkinson's disease and Lewy body dementia 2.5 Migraine coma 2.6 Charles Bonnet syndrome 2.7 Focal epilepsy 3 Tactile hallucinations 4 Scientific explanations 5 Stages of a hallucination 6 In the media 7 See also 8 External links 9 Further reading 10 References

Prevalence

Studies have now shown hallucinatory experiences take place across the world. Previous studies, one as early as 1894,^[2] have reported that approximately 10% of the population experience hallucinations. A recent survey of over 13,000 people^[3] reported a much higher figure with almost 39% of people reported hallucinatory experiences, 27% of which reported daytime hallucinations, mostly outside the context of illness or drug use. From this survey, olfactory (smell) and gustatory (taste) hallucinations seem the most common in the general population. Olfaction (also known as olfactics or smell) refers to the Sense of smell. Taste (or more formally gustation) is a form of direct Chemoreception and is one of the traditional five Senses

Auditory hallucinations

Main article: Auditory hallucinations

Auditory hallucinations, particularly of one or more talking voices, are particularly associated with psychotic disorders such as schizophrenia, and hold special significance in diagnosing these conditions, although many people not suffering from diagnosable mental illness may sometimes hear voices as well. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Psychosis (from the Greek ψυχή "psyche" for mind or soul and -οσις "-osis" for abnormal condition with adjective psychotic Schizophrenia ( from the Greek roots schizein (σχίζειν "to split" and phrēn Mental disorder or mental illness is a psychological or behavioral pattern that occurs in an individual and is thought to cause distress or disability that is not expected as ^[4] The Hearing Voices Movement is a support and advocacy group for people who hallucinate voices, but do not otherwise show signs of mental illness or impairment. Hearing Voices Movement is a philosophical trend in how people who hear voices are viewed Other types of auditory hallucinations include musical hallucinations, where people will hear music playing in their mind, usually songs they are familiar with. One reason this can be caused is by lesions on the brain stem, occurring most often from strokes, but also tumors, encephalitis, or abscesses. A lesion is any abnormal tissue found on or in an organism usually damaged by disease or trauma The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. See also Cancer A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic An abscess (abscessus is a collection of Pus (dead Neutrophils) that has accumulated in a cavity formed by the tissue on the basis of an infectious process ^[5] Other reasons include hearing loss and epileptic activity. Recent reports have also mentioned that it is also possible to get musical hallucinations from listening to music for long periods of time. ^[6]

Hypnagogic hallucination

Main article: Hypnagogia

These hallucinations occur just before falling asleep and affect a surprising number of people in the population. Hypnagogia ( Greek ὕπνος húpnos "sleep" + the root found in ἄγω ágō "to lead away conduct convey" ἀγωγεύς The hallucinations can last from seconds to minutes, all the while the subject usually remains aware of the true nature of the images. These are usually associated with narcolepsy, but can also affect normal minds. Narcolepsy is a Neurological condition most characterized by Excessive Daytime Sleepiness (EDS in which a person falls asleep during the day at inappropriate Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare. ^[7]

Peduncular hallucinosis

Peduncular means pertaining to the peduncle, which is a neural tract running to and from the pons on the brain stem. The pons (sometimes pons Varolii after Costanzo Varolio) is a structure located on the Brain stem. The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. These hallucinations occur most often in the evenings, but not during drowsiness as in the case of hypnagogic hallucination. The subject is usually fully conscious and can interact with the hallucinatory characters for extended periods of time. As in the case of hypnagogic hallucinations, insight into the nature of the images remains intact. Hypnagogia ( Greek ὕπνος húpnos "sleep" + the root found in ἄγω ágō "to lead away conduct convey" ἀγωγεύς The false images can occur in any part of the visual field, and are rarely polymodal. ^[7]

Delirium tremens

Main article: Delerium tremens

One of the most enigmatic forms of visual hallucinations are the highly variable, possibly polymodal delirium tremens. Delirium tremens (colloquially the DTs, " the horrors " " the fear "" the shakes "" jazz hands "" Delirium tremens (colloquially the DTs, " the horrors " " the fear "" the shakes "" jazz hands "" Individuals suffering from delerium tremens may be agitated and confused, especially in the later stages of this disease. Insight is gradually reduced with the progression of this disorder. Sleep is disturbed and occurs for a shorter period of time, with REM overflow. ^[7]

Parkinson's disease and Lewy body dementia

Parkinson's disease is linked with Lewy body dementia for their similar hallucinatory symptoms. Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the Central nervous system that often impairs the sufferer's Dementia with Lewy bodies (DLB is a type of Dementia characterized by abnormal levels of Lewy bodies, a nervous system protein The symptoms strike during the evening in any part of the visual field and are rarely polymodal. The segue into hallucinations may start with illusions^[8] where sensory perception is greatly distorted, but no novel sensory information is present. These typically last for several minutes, during which time the subject may be either conscious and normal or drowsy/inaccessible. Insight into these hallucinations is usually preserved and REM sleep is usually reduced. Parkinson's disease is usually associated with a degraded substantia nigra pars compacta, but recent evidence suggests that PD affects a number of sites in the brain. The substantia nigra ( Latin for "black substance" Sömmering) or locus niger is a heterogeneous portion of the midbrain, separating Some places of noted degradation include the median raphe nuclei, the noradrenergic parts of the locus coeruleus and the cholinergic neurons in the parabrachial and pedunculopontine nuclei of the tegmentum. A receptor is cholinergic if it uses Acetylcholine as its Neurotransmitter. The tegmentum (from Latin for "covering" is a general area within the Brainstem. ^[7]

Migraine coma

This type of hallucination is usually experienced during the recovery from a comatose state. The migraine coma can last for up to two days and a state of depression is sometimes comorbid. In Medicine, comorbidity (literally "additional Morbidity " is either * The presence of one or more disorders (or diseases in addition to The hallucinations occur during states of full consciousness and insight into the hallucinatory nature of the images is preserved. It has been noted that ataxic lesions accompany the migraine coma. ^[7]

Charles Bonnet syndrome

Charles Bonnet syndrome is the name given to visual hallucinations experienced by blind patients. Charles Bonnet syndrome ( CBS) is a disease that causes patients to have hallucinations first described by Charles Bonnet in 1760 The hallucinations can usually be dispersed by opening or closing the eyelids until the visual images disappear. The hallucinations usually occur during the morning or evening, but are not dependent on low light conditions. These prolonged hallucinations usually do not disturb the patients very much as they are aware that they are hallucinating. ^[7]

Focal epilepsy

The visual hallucinations from focal epilepsy are characterized by being brief, and stereotyped. They are usually localized to one part of the visual field and last only a few seconds. Other epileptic features may present themselves between visual episodes. Consciousness is usually impaired in some way, but nevertheless insight into the hallucination is preserved. Usually this type of focal epilepsy is caused by a lesion in the posterior temporoparietal. ^[7]

Tactile hallucinations

Can be associated with substance use, such as someone who feels bugs crawling on them (known as formication) after a prolonged period of cocaine use. Formication is a somewhat unusual but medically well-known abnormal sensation Cocaine ( benzoylmethyl ecgonine) is a Crystalline Tropane Alkaloid that is obtained from the leaves of the Coca plant

Scientific explanations

Various theories have been put forward to explain the occurrence of hallucinations. When psychodynamic (Freudian) theories were popular in psychiatry, hallucinations were seen as a projection of unconscious wishes, thoughts and wants. Psychodynamics, is the systematized study and theory of the psychological forces that underlie human behavior emphasizing the interplay between unconscious and conscious motivation and Sigmund Freud (ˈziːkmʊnt ˈfʁɔʏt born Sigismund Shlomo Freud (May 6 1856 &ndash September 23 1939 was an Austrian Psychiatrist who founded As biological theories have become orthodox, hallucinations are more often thought of (by psychologists at least) as being caused by functional deficits in the brain. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain With reference to mental illness, the function (or dysfunction) of the neurotransmitter dopamine is thought to be particularly important. See Chemical synapse for an introduction to concepts and terminology used in this article Dopamine is a Hormone and Neurotransmitter occurring in a wide variety of animals including both vertebrates and invertebrates ^[9] Psychological research has argued that hallucinations may result from biases in what are known as metacognitive abilities. Psychology (from Greek grc ψῡχή psȳkhē, "breath life soul" and grc -λογία -logia) is an Academic and Metacognition is the Knowledge (ie awareness of one's Cognitive processes and the efficient use of this Self-awareness to self-regulate these cognitive ^[10] These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intentions, memories, beliefs and thoughts). Intention (criminal|Intentions An agent 's intention in performing an action is his or her specific Purpose in doing so the end In Psychology, memory is an organism's ability to store retain and subsequently retrieve information Belief is the psychological state in which an individual holds a Proposition or Premise to be true Thought and thinking are mental forms and Processes respectively ("thought" is both The ability to discriminate between self-generated and external sources of information is considered to be an important metacognitive skill and one which may break down to cause hallucinatory experiences. Information as a concept has a diversity of meanings from everyday usage to technical settings Projection of an internal state or a person's own reaction to another may arise in the form of hallucinations, especially auditory hallucinations. A few scientists have argued that such hallucinations may be the result of other conscious thoughts. A recent hypothesis that is gaining acceptance concerns the role of overactive top-down processing, or strong perceptual expectations, that can generate spontaneous perceptual output (that is, hallucination). ^[11]

Stages of a hallucination

1. Emergence of surprising or warded-off memory or fantasy images ^[12]
2. Frequent reality checks ^[12]
3. Last vestige of insight as hallucinations become “real” ^[12]
4. Fantasy and distortion elaborated upon and confused with actual perception ^[12]
5. Internal-external boundaries destroyed and possible pantheistic experience ^[12]

In the media

Occasionally television programs and movies let the viewer see hallucinations experienced by one of the characters. See Fantasy for an account of the literary genre involving the development of common or popular fantasies Reality, in everyday usage means "the state of things as they actually exist" A form constant is one of several geometric patterns which are recurringly observed during Hallucinations and Altered states of consciousness. Pantheism ( Greek: πάν ( 'pan') = all and θεός ( 'theos') = God it literally means " God is All

1. an episode of Casualty showed a patient's delirium tremens hallucination, live-acted by a tarantula. Casualty is the longest running emergency medical Drama series in the world and the second-longest-running medical drama in the world behind America's General Delirium tremens (colloquially the DTs, " the horrors " " the fear "" the shakes "" jazz hands ""
2. On the ABC show LOST, John Locke sends his protégé Boone on a vision quest via a compound induced hallucination. Lost is an Emmy and Golden Globe award-winning American serial drama television series.
3. In Pirates of the Caribbean: At World's End, Jack Sparrow has hallucinations, seeing a crew made up entirely out of copies of himself. Pirates of the Caribbean At World's End is a 2007 Adventure film, the third film in the ''Pirates of the Caribbean'' series. Captain Jack Sparrow is a Fictional character from the Pirates of the Caribbean franchise who is portrayed by Johnny Depp.
4. In Melrose Place, Dr Kimberely Shaw saw visions of a non-existent personality constantly. Melrose Place is an American primetime soap opera that ran between 1992 and 1999 created by Darren Star for the FOX network and executive produced This hallucination was caused by a tumor pressing against her brain.
5. On Ally McBeal, the main character frequently has a hallucination of a dancing baby, due to the fact that as she gets older, her biological clock ticks faster. Ally McBeal is an American Television series which ran on the FOX network from 1997 to 2002 Allison Marie "Ally" McBeal is the central Fictional character in the Fox Television show Ally McBeal played by Calista Flockhart. The Dancing Baby aka "Baby Cha-Cha" refers to a 3D character and 3D-rendered animation of a baby dancing for several seconds
6. In the TV show Scrubs, hallucinations of hypothetical ridiculous situations are commonplace as gags, such as JD's head blowing up. Scrubs is an Emmy and Peabody Award -winning American Comedy-drama that premiered on October 2 2001 on NBC.
7. In the movie A Scanner Darkly, the characters experience a large amount of drug-induced hallucinations. A Scanner Darkly is a 1977 Science fiction Novel by Philip K Dick.
8. In the movie Dead Man's Shoes the main character spends all his time with a man who is discovered to be a hallucination of his dead brother. Dead Man's Shoes ( 2004) is a British thriller directed by Shane Meadows and written by Shane Meadows and Paddy Considine. These are several examples out of many as hallucinations can add an interesting twist to a movie or show.
9. One larger example is the book and movie Fight Club, where the entire plot line is based on a hallucination of the main character, due to depression, sleep deprivation, and possibly insanity. Fight Club is a 1996 novel by Chuck Palahniuk, chronicling the experiences of an anonymous Protagonist who is struggling with a growing discomfort
10. Numerous examples have appeared in House . House, also known as House MD, is an American Medical drama, which debuted on the FOX network on November 16 2004

See also

• Apparitional experience
• Closed-eye hallucination
• Delusion
• Dimethyltryptamine
• Dream
• Focal seizures
• Folie à deux
• Form constant
• Hallucinations in the sane
• Illusion
• Imaginary friend
• Phantom eye syndrome
• Hallucinogenic drug
• Psychosis
• Simulated reality

External links

• INTERVOICE Online, website of the international hearing voices movement
• Hearing Voices Network
• "Anthropology and Hallucinations", chapter from The Making of Religion
• "The voice inside: A practical guide to coping with hearing voices"

Further reading

• Johnson, Fred H. In Psychology and Parapsychology, an apparitional experience is an anomalous quasi-perceptual experience Closed-eye hallucinations and closed-eye visualizations (CEV are a distinct class of Hallucination. A delusion is commonly defined as a fixed False Belief and is used in everyday language to describe a belief that is either false fanciful or derived from Deception Dimethyltryptamine (DMT also known as NN -dimethyltryptamine, is a naturally occurring Tryptamine and potent psychedelic drug found not only in Dreams are the images sounds thoughts and feelings experienced while Sleeping, particularly strongly associated with Rapid eye movement sleep. Focal seizures (also called partial seizures) are Seizures which affect only a small part of the brain and are split into two main categories Simple partial Folie à deux (literally "a madness shared by two" is a rare psychiatric syndrome in which a symptom of Psychosis (particularly a paranoid A form constant is one of several geometric patterns which are recurringly observed during Hallucinations and Altered states of consciousness. A Hallucination may occur in a person in a state of good mental and physical health even in the apparent absence of a transient trigger factor such as fatigue intoxication or Sensory An illusion is a distortion of the senses revealing how the Brain normally organizes and interprets sensory stimulation Imaginary friends, also known as "imaginary companions" are pretend characters often created by Children. The phantom eye syndrome is a Phantom pain in the eye and visual Hallucinations, after the removal of an eye ( Enucleation, Evisceration) The general group of pharmacological agents commonly known as hallucinogens can be divided into three broad categories Psychedelics, Dissociatives Psychosis (from the Greek ψυχή "psyche" for mind or soul and -οσις "-osis" for abnormal condition with adjective psychotic Simulated reality is the proposition that Reality could be simulated—perhaps by Computer simulation —to a degree indistinguishable from "true" Reality (1978). The Anatomy of Hallucinations. Nelson-Hall.
• Slade, P. D. and Bentall, R. P. (1988). Sensory Deception: a scientific analysis of hallucination. London: Croom Helm.
• Aleman, A. and Larøi, F. (2008). Hallucinations: the science of idiosyncratic perception. Washington, DC: APA Books. http://books.apa.org/books.cfm?id=4318044

References

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