Phosphene
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A Phosphene is the experience of light without light coming into the eye. Phosphenes arise from other forms of stimulation, such as mechanical, electrical, or magnetic of parts of the visual system, or from random firing of cells in the visual system.
The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes. The pressure mechanically stimulates the cells of the retina. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse coloured 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. Christopher Tyler (1978) has published some good drawings of pressure posphenes.
Another common phosphene is "seeing stars", from a sneeze, from a blow on the head, or from low blood pressure (such as on standing up too quickly or prior to fainting). It's possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic stimulation of neurons of the visual cortex or of other parts of the visual system.
Phosphenes have also been created by intense, changing magnetic fields, 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.
Phosphenes have also been created by electricity. Marg and colleagues (c. 1975) inserted stimulating electrodes directly into the visual cortices of blind people, using small pulses of electricity to create phosphenes. These phosphenes were fuzzy spots and bars of colourless or coloured light. Marg and colleagues were hoping to use the phosphenes to allow blind people to see (i.e., by creating a visual prosthesis).
Phosphenes can also be elicited (less commonly) by various diseases of the retina and nerves.
A phosphene could be classified as an example of an entoptic phenomenon.
In 1988, J. D. Lewis-Williams 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", problably enhanced by hallucinogenic drugs.
Phosphenes were used as a learning technique by French scientist and scholar, Francis Lefebure.
Reference
Tyler, C. W. (1978). Some new entoptic phenomena. Vision Research, 18, 1633-1639.
External links
- Entoptic Phenomena: Suzanne Cars comprehensive study of scientific phosphene research (http://www.oubliette.zetnet.co.uk/Intro.html)
- Altered States: Eric Pettifor's review of the above-mentioned article (http://www.wynja.com/arch/entoptic.html)sv:fosfen