I get visual patterns projected onto my field of vision when I have a migraine. They start small and surround the center of my view and then expand outwards until they move out of my field of vision entirely. The process takes about half an hour. I can't look directly at the pattern as it always lies outside and around the focal point. These patterns are brightly colored, translucent and they shimmer and shift — they are not static.

When these ocular migraines first began I experienced them in the workplace, surrounded by all the visual noise and clutter of a busy corporate environment (I was an art director at a publishing company). The first time it happened I thought I might be having a stroke. I read up on them and found that it was a form of migraine. I'd had severe migraines as a boy, but there was no pain to this new phenomenon. Some time later I experienced one of these occurrences while hiking in the woods — and this was an event that provoked some interesting questions.

Within the woods the colors of this ocular event were much more vivid, contrasting with the dark greens and browns of the natural world. It was less of an annoyance and took on the character of an extraordinary event. I began wondering whether ancient humans were susceptible to similar occurrences but, unlike us, they surely wouldn't have had any idea what it was they were experiencing. It must have seemed quite magical — even frightening.

In various cultures it was often a right of passage to go on a "vision quest" as you matured into adulthood. For shamans this was an essential rite. As a part of this procedure it was necessary to perform ritual acts that were supposed to bring about the sought-after vision. Fasting (including refusing water) and sleep deprivation were required — often for days. It therefore intrigues me that my own ocular migraines come about most often because I have have not eaten for some time, or I'm dehydrated, or I'm fatigued.

In his excellent book The Killing of Crazy Horse Thomas Powers writes of a Lakota man known as Horn Chips (Ptehe Woptuha) who was told by the voice of Wakan Tanka to go to a mountain top "and stay there four days with no food or drink." Powers relates "Horn Chips did as the voice directed and was rewarded with a dream in which a snake came to him with instructions." (Horn Chips was to become the medicine man who interpreted the dreams of Crazy Horse and who gave this great warrior the talismans from which he drew his power.)

In some cultures visions were sought by blood-letting, which would have brought about fatigue and perhaps delirium. The shaman priests of the Mayans would draw blood (often from their tongues or penises) and allow it to drip onto paper which they would then burn. The smoke would rise and a "vision serpent" would appear. Many writers have suggested that this vision serpent was represented by the smoke itself, but I wonder if there wasn't more to it than that. Smoke by itself is not an apparition, and the vision serpent was seen as a portal to the Otherworld. Could this fatigue, brought on by the ritual bloodletting, have provoked a vision of the kind I myself experience? Such a vision shimmering brightly in the rising smoke would have seemed magical and could have easily been interpreted as representing an Otherworldly presence. So, while today we can perhaps explain them away, at one time these visions might well have taken on religious and cultural importance.

As stated earlier, you can't focus on these patterns so they are not easy to draw. You can perhaps give a simple impression: spirals, zigzags, dots, rays, triangles and squares — all of these occur in my own ocular visions. The overall appearance is somewhat (semi-) circular or spiral in form and zigzag shapes run throughout. These are among the first forms that appear as art in human culture. Sometimes they are simply scratched into bone or rock. Later they are inscribed or painted onto pottery and, if you look at many ancient pots, you see a circle of zigzags surrounding the opening. It seems that these visual patterns became stylized into some of our most fundamental abstract forms.

Ocular illusions and entoptic phenomena — which include such things as floaters and "stars before your eyes" and so on — are generally considered to have had a connection to early abstract art but there seems to be much disagreement about interpretation and how important this might have been to various prehistoric cultures. Where the experts (David Lewis-Williams, Paul Bahn, and others) seem to disagree most vigorously is over the connection to shamanic practices and whether or not these visual events (and art) might have been connected to ritual and religion. There is also the issue of hallucinogens being used to provoke the visionary experience and the degree to which such drugs might have been used. Going well back in time there is very little to go on, of course, but marijuana has been found in the graves of ancient Eurasian shamans, and peyote and other hallucinogens are known to have been used in the Americas. To me it would seem that the visionary experience (whether linked to religion or not) must go back to the earliest awakenings of human self-consciousness, and explanation and meaning for these strange and intangible experiences would have been needed. The very appearance of these visions — seemingly coming out of nowhere — certainly must have seemed magical and other worldly. What are they? Where do they come from? Why are they here?

My observations on the drug use issue would be two-fold:

a) My own "visions" are NOT drug induced but come about due to a chemical imbalance caused by malnourishment and fatigue. Accordingly, ritual fasting or blood-letting might well induce such visions without the need of drugs.

b) Even if drugs were used they might well have been restricted to a small elite of shaman priests who could carry out the necessary rituals and interpret the visions. In ancient cultures even beer was at first restricted to specific cultural or ritual events. Tobacco was reserved for ritual use. Wine (and even chocolate) was kept for special occasions. In our modern, secular society drugs are considered abhorrent (maybe because they are out of place and out of control) and perhaps their past usage in the rituals of ancient cultures is being discounted or downplayed due to our current biases and distaste.

Much of this is speculative, of course — I'm not an academic and my insights are based as much on intuition as on what I know with any certainty. But I have labelled the interpretive representations of my own experience as "vision serpents" because it seems an appropriate description of the patterned, sensuous and shimmering patterns that appear to me. The deeper questions and associations concerning how ancient humans would have seen and dealt with these visions is something I'll continue to think about.