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Sensory deprivation causes hallucinations (articles)
Visual release hallucinations, also known as Charles Bonnet syndrome (CBS), is the experience of complex visual hallucinations in a person with partial or severe blindness. First described by Charles Bonnet in 1760, it was first introduced into English-speaking psychiatry in 1982.

Signs and symptoms
Mentally healthy people with significant vision loss may have vivid, complex recurrent visual hallucinations (fictive visual percepts). One characteristic of these hallucinations is that they usually are "lilliputian" (hallucinations in which the characters or objects are smaller than normal). The most common hallucination is of faces or cartoons. Sufferers understand that the hallucinations are not real, and the hallucinations are only visual, that is, they do not occur in any other senses, e.g. hearing, smell or taste. Among older adults (> 65 years) with significant vision loss, the prevalence of Charles Bonnet syndrome has been reported to be between 10% and 40%; a recent Australian study has found the prevalence to be 17.5%. Two Asian studies, however, report a much lower prevalence. The high incidence of non-reporting of this disorder is the greatest hindrance to determining the exact prevalence; non-reporting is thought to be a result of sufferers being afraid to discuss the symptoms out of fear that they will be labelled insane.
People suffering from CBS may experience a wide variety of hallucinations. Images of complex colored patterns and images of people are most common, followed by animals, plants or trees and inanimate objects. The hallucinations also often fit into the person's surroundings.
Charles Bonnet, the first person to describe the syndrome.
The disease is named after the Swiss naturalist Charles Bonnet, who described the condition in 1760. He first documented it in his 89-year-old grandfather who was nearly blind from cataracts in both eyes but perceived men, women, birds, carriages, buildings, tapestries, physically impossible circumstances and scaffolding patterns.
The phantom eye syndrome (PES) is a phantom pain in the eye and visual hallucinations after the removal of an eye (enucleation, evisceration).

Many patients experience one or more phantom phenomena after the removal of the eye:
   ● Phantom pain in the (removed) eye (prevalence: 26%)
   ● Non-painful phantom sensations
   ● Visual hallucinations. About 30% of patients report visual hallucinations of the removed eye. Most of these hallucinations consist of basic perceptions (shapes, colors). In contrast, visual hallucinations caused by severe visual loss without removal of the eye itself (Charles Bonnet syndrome) are less frequent (prevalence 10%) and often consist of detailed images.
Visual hallucinations
Enucleation of an eye and, similarly, retinal damage, lead to a cascade of events in the cortical areas receiving visual input. Cortical GABAergic (GABA: Gamma-aminobutyric acid) inhibition decreases, and cortical glutamatergic excitation increases, followed by increased visual excitibility or even spontaneous activity in the visual cortex. It is believed that spontaneous activity in the denervated visual cortex is the neural correlate of visual hallucinations.
Musical ear syndrome (MES) describes a condition seen in people who have hearing loss and subsequently develop auditory hallucinations. "MES" has also been associated with musical hallucinations, which is a complex form of auditory hallucinations where an individual may experience music or sounds that are heard without an external source. It is comparable to Charles Bonnet syndrome (visual hallucinations in visually impaired people) and some have suggested this phenomenon could be included under this diagnosis.

Musical hallucinations and MES have only become widely recognizable in the last few decades of research, but there are indications throughout history that have described symptoms of musical hallucinations. The Romantic composer Robert Schumann was said to have heard entire symphonies in his head from which he drew as inspiration for his music, but later in his life this phenomenon had diminished to just an A note that played ceaselessly within his head. An alternative explanation is that his symptoms were caused by syphilis or mercury poisoning used for its treatment. The Russian composer Dmitri Shostakovich was also recorded as experiencing music hallucinations after some shrapnel was removed from his skull.

The occurrence of MES has been suggested to be very high among the hearing impaired through acquired deafness or the ear condition known as tinnitus. Though exact causation is uncertain, it has been theorized that the "release phenomenon" is taken into effect. The "release phenomenon" says that individuals with acquired deafness may experience musical hallucinations because the lack of stimulation, which can give room for the brain to interpret internal sounds as being external.
Sufferers typically hear music or singing and the condition is more common in women. The hallucinatory experiences differ from that commonly experienced in psychotic disorders although there may be some overlap. The most important distinction is the realization that the hallucinations are not real. Delusional beliefs associated with the hallucinations may occur, but some degree of insight should be preserved. There should not be any other psychotic symptoms present, especially hallucinations in other modalities.

It is postulated that by the "release phenomenon" MES is caused by hypersensitivity in the auditory cortex caused by sensory deprivation, secondary to their hearing loss. This "hole" in the hearing range is "plugged" by the brain confabulating a piece of information – in this case a piece of music. A similar occurrence is seen with strokes of the visual cortex where a visual field defect occurs and the brain confabulates a piece of visual data to fill the spot. This is described by sufferers as an image in the visual field.
The hallucinations are usually not unpleasant but may cause irritation due to their persistent nature. It is common for sufferers to have a history of tinnitus.
Investigations such as magnetic resonance imaging or CT scanning and electroencephalograms (EEGs) may be worthwhile, but will rarely show any serious pathology. It is believed that because this kind of phenomenon is usually heterogenous in causation, a wide variety of factors need to be considered, which could give possible explanation for why MES is seen as under diagnosed. Some of these factors may include significant trauma to the head or any side-effects from substances such as antidepressants, marijuana, alcohol, procaine, or general anesthesia.
The ganzfeld effect (from German for “complete field”) or perceptual deprivation, is a phenomenon of perception caused by exposure to an unstructured, uniform stimulation field. The effect is the result of the brain amplifying neural noise in order to look for the missing visual signals. The noise is interpreted in the higher visual cortex, and gives rise to hallucinations.
It has been most studied with vision by staring at an undifferentiated and uniform field of colour. The visual effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is "seeing black", an apparent sense of blindness. A flickering ganzfeld causes geometrical patterns and colors to appear, and this is the working principle for mind machines and the Dreamachine. The ganzfeld effect can also elicit hallucinatory percepts in many people, in addition to an altered state of consciousness.
Ganzfeld induction in multiple senses is called multi-modal ganzfeld. This is usually done by wearing ganzfeld goggles in addition to headphones with a uniform stimulus.
A related effect is sensory deprivation, although in this case a stimulus is minimized rather than unstructured. Hallucinations that appear under prolonged sensory deprivation are similar to elementary percepts caused by luminous ganzfeld, and include transient sensations of light flashes or colours. Hallucinations caused by sensory deprivation can, like ganzfeld-induced hallucinations, turn into complex scenes.
The effect is a component of a Ganzfeld experiment, a technique used in the field of parapsychology.

In the 1930s, research by psychologist Wolfgang Metzger established that when subjects gazed into a featureless field of vision they consistently hallucinated and their electroencephalograms changed.
The Ganzfeld effect has been reported since ancient times. The adepts of Pythagoras retreated to pitch-black caves to receive wisdom through their visions, known as the prisoner's cinema. Miners trapped by accidents in mines frequently reported hallucinations, visions and seeing ghosts when they were in the pitch dark for days. Arctic explorers seeing nothing but featureless landscape of white snow for a long time also reported hallucinations and an altered state of mind.
A ganzfeld experiment (from the German for “entire field”) is a technique used in parapsychology which claims to be able to test individuals for extrasensory perception (ESP). The ganzfeld experiments are among the most recent in parapsychology for testing telepathy.
Consistent, independent replication of ganzfeld experiments has not been achieved.

Historical context
The ganzfeld was originally introduced into experimental psychology due to the experiments of the German psychologist Wolfgang Metzger (1899-1979) on the perception of a homogenous visual field. In the early 1970s, Charles Honorton had been investigating ESP and dreams at the Maimonides Medical Center and began using the ganzfeld technique to achieve a state of sensory deprivation in which he hypothesised that psi could work. Honorton believed that by reducing the ordinary sensory input, psi conductive states may be enhanced and psi-mediated information could be transmitted.
Since the first full experiment was published by Honorton and Sharon Harper in the Journal of the American Society for Psychical Research in 1974, the Ganzfeld has remained a mainstay of parapsychological research.

Experimental procedure
In a typical ganzfeld experiment, a "receiver" is placed in a room relaxing in a comfortable chair with halved ping-pong balls over the eyes, having a red light shone on them. The receiver also wears a set of headphones through which white or pink noise (static) is played. The receiver is in this state of mild sensory deprivation for half an hour. During this time, a "sender" observes a randomly chosen target and tries to mentally send this information to the receiver. The receiver speaks out loud during the thirty minutes, describing what he or she can see. This is recorded by the experimenter (who is blind to the target) either by recording onto tape or by taking notes, and is used to help the receiver during the judging procedure.
In the judging procedure, the receiver is taken out of the Ganzfeld state and given a set of possible targets, from which they select one which most resembled the images they witnessed. Most commonly there are three decoys along with the target, giving an expected rate of 25%, by chance, over several dozens of trials.
Anton–Babinski syndrome, also known as visual anosognosia, is a rare symptom of brain damage occurring in the occipital lobe. Those who suffer from it are "cortically blind", but affirm, often quite adamantly and in the face of clear evidence of their blindness, that they are capable of seeing. Failing to accept being blind, the sufferer dismisses evidence of their condition and employs confabulation to fill in the missing sensory input. It is named after Gabriel Anton and Joseph Babinski.

Anton–Babinski syndrome is mostly seen following a stroke, but may also be seen after head injury. It is well described by the neurologist Macdonald Critchley:
The sudden development of bilateral occipital dysfunction is likely to produce transient physical and psychical effects in which mental confusion may be prominent. It may be some days before the relatives, or the nursing staff, stumble onto the fact that the patient has actually become sightless. This is not only because the patient ordinarily does not volunteer the information that they have become blind, but he furthermore misleads his entourage by behaving and talking as though they were sighted. Attention is aroused however when the patient is found to collide with pieces of furniture, to fall over objects, and to experience difficulty in finding his way around. They may try to walk through a wall or through a closed door on his way from one room to another. Suspicion is still further alerted when they begin to describe people and objects around them which, as a matter of fact, are not there at all.
Thus we have the twin symptoms of anosognosia (or lack of awareness of defect) and confabulation, the latter affecting both speech and behaviour.
Anton–Babinski syndrome may be thought of ideally as the opposite of blindsight, blindsight occurring when part of the visual field is not consciously experienced, but some reliable perception does in fact occur.

Why patients with Anton–Babinski syndrome deny their blindness is unknown, although there are many theories. One hypothesis is that damage to the visual cortex results in the inability to communicate with the speech-language areas of the brain. Visual imagery is received but cannot be interpreted; the speech centers of the brain confabulate a response.
Patients have also reported visual anosognosia after suffering from ischemic vascular cerebral disease. A 96-year-old man, who was admitted to an Emergency Room complaining of a severe headache and sudden loss of vision, was discovered to have suffered from a posterior cerebral artery thrombosis and consequently lost his vision. He adamantly claimed he was able to see despite an ophthalmologic exam proving otherwise. An MRI of his brain proved that his right occipital lobe was ischemic. Similarly, a 56-year-old woman was admitted to the Emergency Room in a confused state and with severely handicapped psychomotor skills. Ocular movements and pupil reflexes were still intact, but the patient could not name objects and was not aware of light changes in the room, and seemed unaware of her visual deficit.

Case study
Most cases of Anton–Babinski syndrome are reported from adults. The European Journal of Neurology published an article in 2007 that examines a case study of a six-year-old child with Anton–Babinski syndrome and early stages of adrenoleukodystrophy. The child reportedly had abnormal eye movements, would often fall, and would reach for things and often miss his target. When his sight was tested at <20/200 he was still unable to read the large letters on the chart. He denied suffering from headaches, diplopia, or eye pain and seemed unconcerned and unaware of his poor eyesight. Upon examination, his pupils were equal in shape, round, and reactive to light. His mother commented that he developed unusual eye movements and that they had a ″roving quality.″

In popular culture
Anton–Babinski syndrome was featured in two-part episode of the television series House M.D., titled "Euphoria", although it was ascribed to primary amoebic meningoencephalitis, a disease that usually does not cause the syndrome in real life.
The syndrome features prominently in the Rupert Thomson novel The Insult. It is also mentioned in the science fiction novel Blindsight, by Peter Watts.
It is mentioned frequently as "Anton's Blindness" as one of the primary metaphors in Raj Patel's The Value of Nothing.
In Lars von Trier's film Dogville, the character Jack McKay acts as if he can see but gives many signs he can't.
The syndrome is the main theme of Malaysian movie "Desolasi" (Desolation), where the patients live in their own world of imagination, while unable to see the real world.
Closed-eye hallucinations and closed-eye visualizations (CEV) are a distinct class of hallucination. These types of hallucinations generally only occur when one's eyes are closed or when one is in a darkened room. They can be a form of phosphene. Some people report closed-eye hallucinations under the influence of psychedelics. These are reportedly of a different nature than the "open-eye" hallucinations of the same compounds.

Levels of CEV perception
There are five known levels of CEV perception which can be achieved either through chemical stimuli or through meditative relaxation techniques. Level 1 and 2 are very common and often happen every day. It is still normal to experience level 3, and even level 4, but only a small percentage of the population does this without psychedelic drugs, meditation or extensive visualization training.

Level 1: Visual noise
The most basic form of CEV perception that can be immediately experienced in normal waking consciousness involves a seemingly random noise of pointillistic light/dark regions with no apparent shape or order.
This can be seen when the eyes are closed and looking at the back of the eyelids. In a bright room, a dark red can be seen, owing to a small amount of light penetrating the eyelids and taking on the color of the blood it has passed through. In a dark room, blackness can be seen or the object can be more colourful. But in either case it is not a flat unchanging redness/blackness. Instead, if actively observed for a few minutes, one becomes aware of an apparent disorganized motion, a random field of lightness/darkness that overlays the redness/blackness of closed eyelids.
For a person who tries to actively observe this closed-eye perception on a regular basis, there comes a point where if he or she looks at a flat-shaded object with his or her eyes wide open, and tries to actively look for this visual noise, he or she will become aware of it and see the random pointillistic disorganized motion as if it were a translucent overlay on top of what is actually being seen by his or her open eyes.
When seen overlaid onto the physical world, this CEV noise does not obscure physical vision at all, and in fact is hard to notice if the visual field is highly patterned, complex, or in motion. When active observation is stopped, it is not obvious or noticeable, and seemingly disappears from normal physical perception. Individuals suffering from visual snow see similar noise but experience difficulty blocking it from conscious perception.
The noise probably originates from thermal noise exciting the photoreceptor cells in the retina; compare Eigengrau.

Level 2: Light/dark flashes
Some mental control can be exerted over these closed-eye visualizations, but it usually requires a bit of relaxation and concentration to achieve. When properly relaxed it is possible to cause regions of intense black, bright white or even colors such as yellow, green, or pink to appear in the noise. These regions can span the entire visual field, but seem to be fleeting in nature.

Level 3: Patterns, motion, and color
This level is relatively easily accessible to people who use psychedelic drugs such as LSD, and appears to be what most people refer to as colourful visuals.
However, it is also accessible to people involved in deep concentration for long periods of time. When lying down at night and closing the eyes, right before sleep the complex motion of these patterns can become directly visible without any great effort thanks to hypnagogic hallucination. The patterns themselves might resemble fractals.

Level 4: Objects and things
This is a fairly deep state. At this level, thoughts visually manifest as objects or environments. When this level is reached, the CEV noise seems to calm down and fade away, leaving behind an intense flat ordered blackness. The visual field becomes a sort of active space. A side component of this is the ability to feel motion when the eyes are closed.
Opening the eyes returns one to the normal physical world, but still with the CEV object field overlaid onto it and present. In this state it is possible to see things that appear to be physical objects in the open-eye physical world, but that aren't really there.
“If we remember that the essential difference between what we call the real world and the world of imagination and hallucination, is not the elements of which we build them up but the sequence in which these elements appear... then it follows that the sequences directed from without represent a limitation of the otherwise unlimited combinations of the selective forms released at random from within.”
— - Jurij Moskvitin, Essay on the origin of thought.

Level 5: Overriding physical perception
The internal CEV perceptions and think-it/feel-it perceptions become stronger than physical perceptions, and completely override and replace open-eye physical perceptions. This can be a potentially dangerous state if a person is still mobile while in a different perceived world, but by this time most people are motionless and not likely to do something hazardous to themselves or others. This is the point where most hallucinogenic references say it is a good idea to have a "sitter" present to watch over the person using the chemicals, and keep them from accidentally harming themselves or others while deep into their own world.
This level can be entered from complete sensory deprivation, as experienced in an isolation tank, but even there it requires great relaxation.

According to lucid dreaming researcher Stephen LaBerge, perceptions can come from either the senses or imagination. An inhibitory system involving in the thalamus, likely involving serotonergic neurons, inhibits imaginary perceptions from becoming too activated so they turn into hallucinations. This system is inhibited during REM sleep, and the imagination can freely run into the perceptual systems. What happens at level 5 is likely that this system is inhibited, just like in REM sleep, by different causes like sensory deprivation, psychedelic drugs or meditative relaxation techniques.

What is not a CEV

Image burn-in (afterimage)
Image burn-in occurs when very bright objects lie in one's field of vision, and should not be confused with closed-eye hallucinations. Visual burn-in from bright lights is visible for a few minutes after closing the eyes, or by blinking repeatedly, but the burn-in effect slowly fades away as the retina recovers, whereas the waking-consciousness CEV noise will not disappear if observed continuously over a period of time.

Corneal liquid
CEV does not involve the liquid and air bubbles on the surface of the cornea, which can also be seen by extremely nearsighted people when looking at bright point-light sources with glasses/contacts removed. Also called "floater" - often appear as cells floating across the eye. Full-closing and reopening the eyelids creates a very definite wiper-ridge in the corneal liquid that is readily visible. Fully closing and reopening the eyelids also stirs up the corneal liquid which settles down after a brief moment. The motion of waking-consciousness CEV noise is not so directly and physically controllable and repeatable. This is not necessarily only associated with extreme nearsightednes.

Blue-sky sprites
CEV does not seem to be related to the "sprites" (blue field entoptic phenomenon) that can be seen as dots darting around when staring up into a bright blue sky on a sunny day (not looking at the sun). These dots superimposed over a flat blue background are white blood cells moving through the blood vessels of the retina. The motion of waking-consciousness CEV noise is uniformly random compared to the waking-consciousness blue-sky sprite motion.

Physical retinal stimulation
CEV is unrelated to the visual noise seen when the retina is physically stimulated. The retina can be made to produce light patterns of visual noise simply by one rubbing their eyes somewhat forcefully in a manner that increases intraocular pressure. Additionally retinal noise can be produced by touching near the rear of the eyeball producing pressure phosphenes (for example, if one closes one's eyes, looks all the way left, and lightly touches the rightmost part of the eye socket, this produces visual noise in the shape of a circle that appears at the left side of the visual field - a practice that is neither painful nor dangerous). None of these are closed-eye hallucinations.
The Prisoner's cinema is a phenomenon reported by prisoners confined to dark cells and by others kept in darkness, voluntarily or not, for long periods of time. It has also been reported by truck drivers, pilots, and practitioners of intense meditation. Astronauts and other individuals who have been exposed to certain types of radiation have reported witnessing similar phenomena.
The "cinema" consists of a "light show" of various colors that appear out of the darkness. The light has a form, but those that have seen it find it difficult to describe. Sometimes, the cinema lights resolve into human or other figures.
Scientists believe that the cinema is a result of phosphenes combined with the psychological effects of prolonged exposure to darkness. Others have noted a connection between the form the lights take and neolithic cave paintings.

Popular culture
The pilot episode for the original Twilight Zone series, "Where Is Everybody?," depicts elaborate, fully realistic hallucinations by a test subject undergoing prolonged isolation and sensory deprivation as part of research into human space travel.
Dark retreat (Wylie: mun mtshams) refers to advanced practices in the Taoism, Dzogchen lineages of the Nyingmapa, Bönpo, other schools of Tibetan Buddhism. A dark retreat is a solo retreat in a space that is completely absent of light. Because there is no optical stimulation, one can experience "prisoner's cinema", commonly known as the lights. The time period dedicated to dark retreat varies from a few hours to decades. Dark Retreat in the Himalayan tradition is a restricted practice only to be engaged by the senior spiritual practitioner under appropriate spiritual guidance. This practice is considered conducive for navigating the bardo at the time of death and for realising the rainbow body. The traditional dark retreat requires stability in the natural state and is only suitable for advanced practitioners. Ayu Khandro and Dilgo Khyentse are examples of modern, if not contemporary, practitioners of significant periods of Dark Retreat sadhana.
Czech Television reporter, Silvie Dymáková (winner of the main prize for documentary filmmaking in the Czech Republic "Czech Lion award"), decided to spend a week in perfect darkness. No mobile, no music, no people, with no awareness of time. And because Silvie documented her feelings on thermographic camera, you will see a unique testimony to how it is to be alone in the dark and silence for seven days.
Ayu Khandro performed the Yang-Ti (Tibetan), an advanced practice of the Dzogchen Upadesha, a version of the Dark Retreat.
An account of extensive experiences with dark retreat, Dawning of Clear Light: A Western Approach to Tibetan Dark Retreat Meditation, was written by Martin Lowenthal.

Some spiritual traditions have used similar techniques in the pursuit of enlightenment: Kogi people spend 9 years in dark caves or huts in Colombia, in Europe, the dark room appeared as a network of tunnels, in Egypt as the Pyramides, in Rome as the catacombs, by the Essenes in Israel and Taoists in China as caves.
The meaning of a spiritual retreat can be different for different religious communities. Spiritual retreats are an integral part of many Hindu, Buddhist, Christian and Sufi (Islamic) communities.
In Hinduism and Buddhism, meditative retreats are seen by some as an intimate way of deepening powers of concentration and insight.
Retreats are also popular in Christian churches, and were established in today's form by St. Ignatius of Loyola (1491-1556), in his Spiritual Exercises. Ignatius was later to be made patron saint of spiritual retreats by Pope Pius XI in 1922. Many Protestants, Catholics and Orthodox Christians partake in and organize spiritual retreats each year.
Meditative retreats are an important practice in Sufism, the mystical path of Islam. The Sufi teacher Ibn Arabi's book Journey to the Lord of Power (Risālat al-Anwār) is a guide to the inner journey that was published over 700 years ago.

A retreat can either be a time of solitude or a community experience. Some retreats are held in silence, and on others there may be a great deal of conversation, depending on the understanding and accepted practices of the host facility and/or the participant(s). Retreats are often conducted at rural or remote locations, either privately, or at a retreat centre such as a monastery. Some retreats for advanced practitioners may be undertaken in darkness, a form of retreat that is common as an advanced Dzogchen practice in the Nyingma school of Tibetan Buddhism.
Spiritual retreats allow time for reflection, prayer, or meditation. They are considered essential in Buddhism, having been a common practice since the Vassa, or rainy season retreat, was established by the founder of Buddhism, Gotama Buddha. In Zen Buddhism retreats are known as sesshin.

The Christian retreat can be defined in the most simplest of terms as a definite time (from a few hours in length to a month) spent away from one's normal life for the purpose of reconnecting, usually in prayer, with God. Although the practice of leaving one's everyday life to connect on a deeper level with God, be that in the desert (as with the Desert Fathers), or in a monastery, is as old as Christianity itself, the practice of spending a specific time away with God is a more modern phenomenon, dating from the 1520s and St. Ignatius of Loyola's composition of the Spiritual Exercises. Jesus fasting in the desert for forty days is used as a biblical justification of retreats.

Roman Catholicism
In the 20th Century, three-day retreats were popularised by the Cursillo movement, based on Ignatian spirituality.
The retreat was popularised in Roman Catholicism by the Society of Jesus (Jesuits), whose founder, St. Ignatius of Loyola, as a layman began, in the 1520s, directing others in making (participating in) the exercises. Another form the Exercises came in, which became known as the nineteenth "Observation", 'allowed continuing one's ordinary occupations with the proviso of setting aside a few hours a day for this special purpose.' The spiritual exercises were intended for people wanting to live closer to God's will for their life.
Following the growth of the Cursillo movement in Spain, similar retreats have become popular, either using licensed Cursillo material or independent material loosely based on its concepts, leading to the development of the three day movement.
There are spiritual retreats with various themes that aid to reform, re-adapt and re-ensure christian values, principles and scriptural understanding in personal and family lives. There are Retreats held by church as consultants to help keep family life in touch and connection in a busy world.

Sufi retreats or spiritual khalwa
The translation of khalwa from Arabic is seclusion or separation, but it has a different connotation in Sufi terminology: It is the act of total self-abandonment in desire for the Divine Presence. In complete seclusion, the Sufi continuously repeats the name of God as a highest form of dhikr (remembrance of God meditation). In his book, Journey to the Lord of Power, Muhiyid-Did ibn Arabi (1165-1240 A.D.) discussed the stages through which the Sufi passes in his khalwa.
Ibn Arabi suggested: "The Sufi should shut his door against the world for forty days and occupy himself with remembrance of Allah, that is to keep repeating, "Allah, Allah..." Then, "Almighty God will spread before him the degrees of the kingdom as a test. First, He will discover the secrets of the mineral world. If he occupies himself with dthikr, He (God) will unveil to the secrets of the vegetable world, then the secrets of the animal world, then the infusion of the world of life-force into lives, then the "surface sign" (the light of the Divine Names, according to Abdul-Karim al-Jeeli, the book's translator), then the degrees of speculative sciences, then the world of formation and adornment and beauty, then the degrees of the qutb (the soul or pivot of the universe-see #16) Then he will be given the divine wisdom and the power of symbols and authority over the veil and the unveiling. The degree of the Divine Presence is made clear to him, the garden (of Eden) and Hell are revealed to him, then the original forms of the son of Adam, the Throne of Mercy. If it is appropriate, he will know his destination. Then he will reveal to him the Pen, the First Intellect (as it is called by Sufi philosophers), then the Mover of the Pen, the right hand of the Truth. (The "Truth" as defined by al-Jeeli is that by which everything is created, none other than God most High.)
The practice of khalwah is regularly followed by the Sufis, with the permission and the supervision of a Sufi authority.
The Sufis base the assigning of forty days of khalwa period on the forty days Allah had appointed for Musa (Moses) as a fasting period before speaking to him, as mentioned in different chapters in the Qur'an. One of them is from surat al-Baqarah.
Khalwa is still practiced today amongst authorized Sheikhs, such as Mawlana Sheikh Nazim Al-Haqqani, Lefka, Cyprus.
Синдром Шарля Бонне — это состояние пациента с серьёзными расстройствами зрения, при котором он видит галлюцинации. Впервые был описан Шарлем Бонне в 1760 г.

У психически здоровых людей с серьёзными нарушениями зрительной системы появляются галлюцинации разных уровней сложности: от геометрических до достаточно подробных галлюцинаций с фигурами и, в особенности, с лицами. Лица, и иногда искажённые лица, чаще всего встречаются во всех этих галлюцинациях. Один из следующих по распространённости признаков — мультфильмы (они прозрачны и накрывают поле зрения, как экран). Люди, подверженные данному заболеванию, понимают, что их галлюцинации нереальны и являются только зрительными т.е не затрагивают остальные системы органов чувств. Для таких видений типично, что они могут мгновенно появляться и мгновенно исчезать. Обычно они не угасают и не появляются. Они внезапны, и меняются так же внезапно.
Галлюцинации Шарля Бонне не направлены на больного, что является их основной отличительной чертой от галлюцинаций психотического характера.

Среди пожилых людей, с существенными расстройствами зрения, распространённость синдрома Шарля Бонне, по разным данным, составляет от 10 до 15 %. Невозможно точно подсчитать распространённость данного заболевания, так как многие больные слишком напуганы, что их сочтут за душевнобольных и, поэтому, не рассказывают врачам о своих видениях.

Галлюцинозу Шарля Бонне подвержены люди с ухудшенным зрением. Причинами упадка зрения могут, в частности, стать: макулярная дегенерация, глаукома, катаракта, двустороннее повреждение зрительного нерва из-за отравления метанолом, опухоли в затылочной коре головного мозга и т. п. По мере того, как человек теряет зрение, зрительный отдел коры головного мозга больше не получают входящих сигналов. Он становится гиперактивным и возбудимым и начинает самопроизвольно запускаться. Вследствие этого и появляются самые разнообразные галлюцинации. Что именно человек увидит в своих видениях зависит от того, какие группы нейронов самоактивируются.

На сегодняшний день не существует эффективного лечения синдрома Шарля Бонне. Обычно галлюцинации пропадают самостоятельно через год или полтора, но сроки для каждого человека могут отличаться. По-видимому, есть некоторые действия, способные остановить галлюцинации. Образы иногда исчезают, если закрыть глаза или поморгать.

Впервые описавший этот синдром в 18 веке Шарль Бонне сам им не страдал. Галлюцинации были у его дедушки — Шарля Люллена. Он перенёс операцию по поводу катаракты, и его зрение было довольно плохим. И, в 1759 году, он описал внуку свои разнообразные видения.
Первое, что он описал, это то, как он видел носовой платок в воздухе. Большой голубой носовой платок с четырьмя оранжевыми кругами. Он знал, что это галлюцинация, потому что платков в воздухе не бывает. Потом он увидел большое колесо на горизонте. Но иногда он не был уверен в том — видит ли он сейчас галлюцинацию или нет, потому что галлюцинации могли подходить к зрительному контексту. Один раз у него в гостях были внучки. Он спросил: «Кто эти красивые молодые люди с вами?» Они ответили: «Увы, дедушка, с нами нет никаких красивых молодых людей». И тогда красивые молодые люди исчезли.
Шарль Люллен видел сотни разных фигур, различные пейзажи всех видов. Однажды он увидел человека в халате, курившего трубку, и понял, что это он сам и есть. Это единственный персонаж, которого он узнал.