Phosphene
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- "Phosphene" is also a common alternate spelling of Phosphine, PH₃, a toxic and explosive gas.
A phosphene is an entoptic phenomenon characterized by the sensation of light from mechanical, electrical, or magnetic stimulation of the eye's retina, or from random firing of cells in the visual system, rather than from light.
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 phosphenes.
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. For example, Brindley and Rushton (1974) inserted a matrix of stimulating electrodes directly into the visual cortex of a 64-year-old blind man, using small pulses of electricity to create phosphenes. These phosphenes were points, spots, and bars of colourless or coloured light. Brindley and Rushton used the phosphenes to create a visual prosthesis, in this case by using the phosphenes to depict Braille spots.
Phosphenes can also be elicited (less commonly) by various diseases of the retina and nerves.
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", probably enhanced by hallucinogenic drugs.
Phosphenes were used as a learning technique by French scientist and scholar, Francis Lefebure.
References
Brindley, G. S., & Rushton, D. N. (1974). Implanted stimulators of the visual cortex as visual prosthetic devices. Transactions of the American Academy of Ophthalmology & Otolaryngology, 78, 741-745.
Tyler, C. W. (1978). Some new entoptic phenomena. Vision Research, 18, 1633-1639.