Entoptic visuals are a physiological effect that can be produced naturally in the visual processing center of any human. Not to be confused with optical illusions, they are visual sensations produced by mechanisms within the eye, namely in relation to the retina and under certain conditions.
They often occur in linear zig-zag patterns, dots, and other abstract shapes, and can be caused by mechanisms including the movement of white blood cells in capillaries in front of the retina or floating coagulations of vitreous jelly within the eye. Other shapes produced by these documented phenomena include hourglass or bow-tie shapes, arcs, squiggly lines, and the “Purkinje Tree”, which is a visual imprint of the blood vessels within one’s own eye that can be seen when light shines into the pupil from an opportune angle. One can also produce a phosphene, or the perception of light and veiny or zig-zag-like lines by applying pressure to the closed eye.
Most of these phenomena are caused by the viewing of a plain, solid background such as a clear sky. Needless to say, the phenomena could easily be encountered in daily life when outdoors. Another interesting phosphene-related visual phenomenon called “Prisoner’s Cinema” is known to occur when one is confined in darkness for extended periods of time. It presents as a “light show” in the darkness that can be amorphous but eventually takes familiar human or animal forms. It has commonly been noted by people practicing intense meditation or activities requiring long-term mental focus, such as pilots, astronauts, and truck drivers. It is easy to imagine how the conditions of life in a cave might produce this effect, and the possible connection to cave art has been noted by researchers. It is certainly reminiscent of some more abstract cave art forms, such as Chauvet Cave’s pointillism-style bison discussed in my post on hand motifs. More interestingly, all of the described entoptic phenomena thus far are also known to be produced by the brain during epileptic fits, migraines, and altered states of consciousness.
Other researchers have studied art produced by schizophrenic patients and found striking similarities to entoptic figures. This has been linked to another type of entoptic imagery, called a ‘form-constant,’ thought to be produced in the visual cortex. These images are often geometric in style and linked to the nervous system. The “viewer” might associate them or mentally connect them with a familiar image or pattern, in which case they’re considered visual hallucinations. This type of entoptic imagery is often noted during altered states produced by use of entheogens or “natural” trance states induced by behaviors such as meditation and fasting. It is also seen in schizophrenics.
Research into entoptic visuals caused by mental imbalances and entheogens has shown that certain structural similarities found in entoptic imagery are experienced by many different individuals and through many different methods of induction. These similar visuals, or ‘form-constants’, were shown in 1964 in a study by M.J. Horowitz.
The striking similarity of many of these entoptic images to humanity’s earliest-known symbolic imagery and geometric designs has caught the attention of a number of neurocognitive researchers. These researchers have incorporated them into a cognitive neurological framework that places entoptics and several other cognitive mechanisms at the critical juncture of humanity’s first verified demonstration of symbolic practice. That is, these designs “came first,” so to speak, physiologically and later were given symbolic meaning and totemic functions within a social system. They might also be associated with the rise of early animistic belief or possibly shamanistic behaviors associated with hallucination and trance states, as seen in a number of documented cultures globally.
Evidence for this physiological origin includes the prominence of classic entoptic designs such as nested curves, cross-hatching, dots, and zig-zag patterns in the earliest known forms of human symbolic expression separate from self-adornment– for example, the incised ochre blocks at Blombos Cave from the Middle Stone Age, dated to approximately 100,000 BC and discussed in more detail in my previous post. These are humanity’s earliest known symbolic objects. They’re also accompanied by similarly-decorated objects found at other cave sites in South Africa that seemed to appear around that geographic area in the same period.
The developmental timeframes of the sociocognitive and physiological structures necessary to make these connections are unknown and will never truly be known. However, it is likely that, given the slow pace of evolutionary change in our brains and bodies, Homo sapiens‘ transition toward symbolic behavior (assuming the validity of the neurocognitive model) developed gradually over time rather than in an abrupt or “revolutionary” way. It seems possible that human cognitive complexity and symbolic behavior began even before the Middle Stone Age, but that material evidence for it either was subject to differential preservation outside of caves or hasn’t yet been found.
The following videos describe the history and science behind entoptic phenomena, as well as how to produce them yourself!
1. Morriss-Kay, Gillian M. 2010. The evolution of human artistic creativity. Journal of Anatomy, 216, 158-176.
2. Balter, M. 2009a. Early start for human art? Ochre may revise timeline.
3. Balter, M. 2009b. On the Origin of Art and Symbolism. Science, 323, 709-711.
5. Murchie, Guy. 1998. The Seven Mysteries of Life: An Exploration in Science and Philosophy. Houghton Mifflin Harcourt. p. 237. ISBN 0-395-95791-5.