Phosphene
Encyclopedia
A phosphene is a phenomenon characterized by the experience of seeing light
without light actually entering the eye
. The word phosphene comes from the Greek words phos (light) and phainein (to show). Phosphenes are flashes of light, often associated with optic neuritis
, induced by movement or sound.
Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina
or visual cortex
as well as by random firing of cells in the visual system
. Phosphenes have also been reported by meditators
(commonly called nimitta); people who go for long periods without visual stimulation (also known as the prisoner's cinema
); or those who are using psychedelic drug
s.
phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks. The pressure mechanically stimulates the cells of the retina
. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light. Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene. Hermann von Helmholtz
and others have published drawings of their pressure phosphenes.
One example of a pressure phosphene is demonstrated by gently pressing the side of your eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.
Another common phosphene is “seeing stars,” from a sneeze
, a heavy and deep cough, blowing of the nose, a blow on the head or low
blood pressure
(such as on standing up too quickly or prior to fainting). It is possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic stimulation of neuron
s of the visual cortex
or of other parts of the visual system.
Less commonly, phosphenes can also be caused by some diseases of the retina and nerves, for example multiple sclerosis
. The British National Formulary lists phosphenes as an occasional side effect of at least one anti-anginal medication (available only by medical prescription in the United Kingdom).
The name "phosphene" was coined by JBH Savigny, better known as the ship's surgeon of the wrecked Medusa
. It was first employed by Serre d'Uzes to test retinal function prior to cataract surgery.
Otfrid Foerster
. Brindley and Lewin (1968) inserted a matrix of stimulating electrodes directly into the visual cortex
of a 52-year-old blind
man, using small pulses of electricity
to create phosphenes. These phosphenes were points, spots, and bars of colorless or colored light. Brindley and Rushton (1974) used the phosphenes to create a visual prosthesis, in this case by using the phosphenes to depict Braille
spots.
In recent years, researchers have successfully developed experimental brain-computer interfaces or neuroprosthesis that stimulate phosphenes to restore vision to people blinded through accidents. Notable successes include the human experiments by William H. Dobelle
and Mark Humayun and animal research by Dick Normann.
Experiments with humans have shown that when the visual cortex is stimulated above the calcarine fissure
phosphenes are produced in the lower part of the visual field, and vice versa.
s, such as with transcranial magnetic stimulation
. These fields can be positioned on different parts of the head to stimulate cells in different parts of the visual system. They also can be induced by alternating current
s that entrain neural oscillation as with trancranial alternating-current stimulation. In this case they appear in the peripheral visual field
.
Astronauts exposed to radiation in space report seeing phosphenes.
and T. A. Dowson published an article about phosphenes and other entoptic phenomena. They argued, among other things, that non-figurative art of the Upper Paleolithic
depicts actual visions of phosphenes and neurological “form constants,” probably enhanced by hallucinogenic
drugs
.
Phosphenes were used as a learning technique by French scientist and scholar, Francis Lefebure
- this is called "phosphenism".
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
without light actually entering the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
. The word phosphene comes from the Greek words phos (light) and phainein (to show). Phosphenes are flashes of light, often associated with optic neuritis
Optic neuritis
Optic neuritis is the inflammation of the optic nerve that may cause a complete or partial loss of vision.-Causes:The optic nerve comprises axons that emerge from the retina of the eye and carry visual information to the primary visual nuclei, most of which is relayed to the occipital cortex of the...
, induced by movement or sound.
Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
or visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
as well as by random firing of cells in the visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
. Phosphenes have also been reported by meditators
Meditation
Meditation is any form of a family of practices in which practitioners train their minds or self-induce a mode of consciousness to realize some benefit....
(commonly called nimitta); people who go for long periods without visual stimulation (also known as the prisoner's cinema
Prisoner's cinema
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...
); or those who are using psychedelic drug
Psychedelic drug
A psychedelic substance is a psychoactive drug whose primary action is to alter cognition and perception. Psychedelics are part of a wider class of psychoactive drugs known as hallucinogens, a class that also includes related substances such as dissociatives and deliriants...
s.
Mechanical stimulation
The most common phosphenes are pressurePressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks. The pressure mechanically stimulates the cells of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light. Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene. Hermann von Helmholtz
Hermann von Helmholtz
Hermann Ludwig Ferdinand von Helmholtz was a German physician and physicist who made significant contributions to several widely varied areas of modern science...
and others have published drawings of their pressure phosphenes.
One example of a pressure phosphene is demonstrated by gently pressing the side of your eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.
Another common phosphene is “seeing stars,” from a sneeze
Sneeze
A sneeze is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa...
, a heavy and deep cough, blowing of the nose, a blow on the head or low
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
(such as on standing up too quickly or prior to fainting). It is possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic stimulation of neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s of the visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
or of other parts of the visual system.
Less commonly, phosphenes can also be caused by some diseases of the retina and nerves, for example multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
. The British National Formulary lists phosphenes as an occasional side effect of at least one anti-anginal medication (available only by medical prescription in the United Kingdom).
The name "phosphene" was coined by JBH Savigny, better known as the ship's surgeon of the wrecked Medusa
Medusa (ship)
The Méduse was a 40-gun Pallas-class frigate of the French Navy, launched in 1810. She took part in the Napoleonic wars, namely in the late stages of the Mauritius campaign of 1809–1811 and in raids in the Caribbean....
. It was first employed by Serre d'Uzes to test retinal function prior to cataract surgery.
Electrical stimulation
Phosphenes have also been created by electrical stimulation of the brain as early as 1929 by neurologistNeurologist
A neurologist is a physician who specializes in neurology, and is trained to investigate, or diagnose and treat neurological disorders.Neurology is the medical specialty related to the human nervous system. The nervous system encompasses the brain, spinal cord, and peripheral nerves. A specialist...
Otfrid Foerster
Otfrid Foerster
Otfrid Foerster was a German neurologist and neurosurgeon, who made innovative contributions to neurology and neurosurgery, such as rhizotomy for the treatment of spasticity, anterolateral cordotomy for pain, the hyperventilation test for epilepsy, Foerster's syndrome, the first electrocorticogram...
. Brindley and Lewin (1968) inserted a matrix of stimulating electrodes directly into the visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
of a 52-year-old blind
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
man, using small pulses of electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
to create phosphenes. These phosphenes were points, spots, and bars of colorless or colored light. Brindley and Rushton (1974) used the phosphenes to create a visual prosthesis, in this case by using the phosphenes to depict Braille
Braille
The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...
spots.
In recent years, researchers have successfully developed experimental brain-computer interfaces or neuroprosthesis that stimulate phosphenes to restore vision to people blinded through accidents. Notable successes include the human experiments by William H. Dobelle
William H. Dobelle
William H. Dobelle was a biomedical researcher who developed experimental technologies that restored limited sight to blind patients. In addition, Dobelle is known for the major impact that he and his company have had on the breathing pacemaker and the medical community as a whole. He was...
and Mark Humayun and animal research by Dick Normann.
Experiments with humans have shown that when the visual cortex is stimulated above the calcarine fissure
Calcarine fissure
The calcarine fissure is an anatomical landmark located at the caudal end of the medial surface of the brain. Its name comes from the Latin "calcar" meaning "spur."-Anatomy:...
phosphenes are produced in the lower part of the visual field, and vice versa.
Other causes
Phosphenes have also been created by intense, changing magnetic fieldMagnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s, such as with transcranial magnetic stimulation
Transcranial magnetic stimulation
Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain...
. These fields can be positioned on different parts of the head to stimulate cells in different parts of the visual system. They also can be induced by alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
s that entrain neural oscillation as with trancranial alternating-current stimulation. In this case they appear in the peripheral visual field
Peripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
.
Astronauts exposed to radiation in space report seeing phosphenes.
Explanation
Most vision researchers believe that phosphenes result from the normal activity of the visual system after stimulation of one of its parts from some stimulus other than light. For example, Grüsser et al. showed that pressure on the eye results in activation of retinal ganglion cells in a similar way to activation by light. An ancient, discredited theory is that light is generated in the eye. A version of this theory has been revived, except, according to its author, that "phosphene lights are [supposed to be] due to the intrinsic perception of induced or spontaneous increased biophoton emission of cells in various parts of the visual system (from retina to cortex)"Anthropological research
In 1988, David Lewis-WilliamsDavid Lewis-Williams
James David Lewis-Williams is a South African scholar. He is professor emeritus of cognitive archaeology at the University of the Witwatersrand in Johannesburg....
and T. A. Dowson published an article about phosphenes and other entoptic phenomena. They argued, among other things, that non-figurative art of the Upper Paleolithic
Upper Paleolithic
The Upper Paleolithic is the third and last subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. Very broadly it dates to between 40,000 and 10,000 years ago, roughly coinciding with the appearance of behavioral modernity and before the advent of...
depicts actual visions of phosphenes and neurological “form constants,” probably enhanced by hallucinogenic
Psychedelics, dissociatives and deliriants
This general group of pharmacological agents can be divided into three broad categories: psychedelics, dissociatives, and deliriants. These classes of psychoactive drugs have in common that they can cause subjective changes in perception, thought, emotion and consciousness...
drugs
Psychoactive drug
A psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...
.
Phosphenes were used as a learning technique by French scientist and scholar, Francis Lefebure
Francis Lefebure
Dr. Francis Lefebure was a French physician, known for his study of phosphenes.-Early life:Lefebure was born in Paris, France. His mother, Claire de Saint-Rémy, was a famous painter and poet. His father, a lawyer, published a magazine about thermal and tourist laws...
- this is called "phosphenism".
See also
- DiphospheneDiphospheneIn chemistry, a diphosphene is an organophosphorus compound that has a phosphorus-phosphorus double bond, denoted by R-P=P-R'. These compounds are not common but are of theoretical interest. Normally, compounds with the empirical formula RP exist as rings. However, when the organic substituent is...
- Visual snowVisual snowVisual snow is a transitory or persisting visual symptom where people see snow or television-like static in parts or the whole of their visual fields, especially against dark backgrounds...
- Prisoner's cinemaPrisoner's cinemaThe 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...
- Scintillating scotomaScintillating scotomaScintillating scotoma is the most common visual aura preceding migraine and was first described by 19th century physician Hubert Airy . It is often confused with ocular migraine which originates in the eyeball or socket.-Presentation:...
- Closed-eye hallucinationClosed-eye hallucinationClosed-eye hallucinations and closed-eye visualizations 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 are a form of phosphene....
- Dark retreatDark retreatDark retreat refers to advanced practices in the Dzogchen lineages of the Nyingmapa, Bönpo and other schools of Tibetan Buddhism.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...
- Floatation tank
- Francis LefebureFrancis LefebureDr. Francis Lefebure was a French physician, known for his study of phosphenes.-Early life:Lefebure was born in Paris, France. His mother, Claire de Saint-Rémy, was a famous painter and poet. His father, a lawyer, published a magazine about thermal and tourist laws...