The human brain in all it’s vast meat-based computational prowess always seems to end up back at some variation of the geometric tunnel type of sensory experience. Drugs, warp speed, mental illness, near-death experience, a swift jab in the eyeball- they all seem to bring on similar familiar zooming/pulsing/spiralling tunnel-vision-like patterns. Why is that?

Geometric hallucinations were first studied systematically in the 1920s by the German-American psychologist Heinrich Klüver. Klüver’s interest in visual perception had led him to experiment with peyote, that cactus made famous by Carlos Castaneda, whose psychoactive ingredient mescaline played an important role in the shamanistic rituals of many central American tribes. Mescaline was well-known for inducing striking visual hallucinations.

Uncoiling the spiral: Maths and hallucinations via io9