There is a term for the little glowing shapes that temporarily appear when you rub your eyes or bang your head – phosphenes. In the 1930s, a German scientist found ways to make them appear via the use of electricity, and later the use of drugs.

Phosphenes can be caused by all kinds of things. The simplest ones are the little points of light that appear whenever you rub your eyes. Things get a little more complex when you take a hit to the head. Smacks to the visual cortex tend to result in people “seeing stars.”


In the 1930s, one scientist found a more reliable, and less bruising, way to produce phosphenes. An electrical engineer by training, he found he could use electromagnetic waves to stimulate the brain. By varying the frequency of the waves by less than ten percent he found he could produce a “great number” of forms.

Eventually, he came up with fifteen different shapes that most people were likely to see. They could be variations on circular shapes, like radials, concentric circles, or spirals. They could also lines arranged in patterns like lattices, waves, and poles. (Personally I think he’s being too vague when he gets to the eighth group, which he just classifies as “odd figures.”)


Soon electrical stimulation wasn’t enough, and Knoll decided to give his experimental subjects LSD, psilocybin, and mescaline. The drugs, Knoll discovered, increased the number of phosphenes produced by electrical stimulation, and made them more vivid, but didn’t alter the shapes.

Many people, looking at Knoll’s work, notice a similarity between the phosphenes and cave art. Could ancient people have taken phosphenes as inspiration for their more abstract work? Or were they actually chronicling what they saw, the same way they chronicled birds and ruminants? What do you think?

Top Image: Tiago Sousa