A form constant is one of several geometric patterns which are recurringly observed by different people during hallucinatory states.

In 1926, Heinrich Klüver systematically studied the effects of mescaline (peyote) on the subjective experiences of its users. In addition to producing potent hallucinations characterized by bright, 'highly saturated' colors and vivid imagery, Klüver noticed that mescaline produced recurring geometric patterns in different users. He called these patterns 'form constants' and categorized four types: lattices (including honeycombs, checkerboards, and triangles), cobwebs, tunnels, and spirals.

Klüver's form constants have appeared in other drug-induced and naturally-occurring hallucinations, suggesting a similar physiological process underlying hallucinations with different triggers. Klüver's form constants also appear in near-death experiences and hallucinations of those with synesthesia. Other triggers include psychological stress, or threshold consciousness, including falling asleep, waking up, insulin hypoglycemia, the delirium of fever, epilepsy, psychotic episodes, advanced syphilis, sensory deprivation, photostimulation, electrical stimulation, crystal gazing, migraine headaches, dizziness and a variety of drug intoxications.

The diversity of conditions that provoke such patterns suggests that form constants reflect some fundamental property of the visual system.

See also

• Tessellation
• Moiré pattern

References

1. Blackmore, Susan. Dying to Live: Near-Death Experiences. Buffalo, NY: Prometheus Books, 1993.
2. Bressloff, Paul C., Jack D. Cowan, Martin Golubitsky, Peter J. Thomas, and Matthew C. Wiener. "What Geometric Visual Hallucinations Tell Us About the Visual Cortex." Neural Computation. Vol. 14, No. 3 (March 2002): 473-491.
3. Cytowic, Richard E., The Man Who Tasted Shapes.
4. Ermentrout,G.B. and Cowan, J.D., "A mathematical theory of visual hallucination patterns." Biol. Cybernet. 34 (1979), no. 3, 137-150.