A form constant is one of several geometric patterns which are recurringly observed during hallucinations and altered states of consciousness. They are also encountered during Lucid Dreaming before the actual dream.
In 1926, Heinrich Klüver systematically studied the effects of psychedelics on the subjective experiences of its users. In addition to producing 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, cobwebs, tunnels, and spirals.
Many of these shapes have an intriguing similarity to much of the imagery in Ernst Haeckel’s Artforms in Nature, which includes over 100 detailed illustrations of microscopic animals and sea creatures.
Klüver’s form constants have appeared in other 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, sensory deprivation, electrical stimulation, crystal gazing and migraine headaches. These shapes may appear on their own or with eyes shut in the form of phosphenes, especially when exerting pressure against the closed eyelid.
Author Michael Moorcock once observed in print that the shapes he had seen during his migraine headaches resembled exactly the form of fractals. The diversity of conditions that provoke such patterns suggests that form constants reflect some fundamental property of visual perception.
The practice of the ancient art of divination may suggest a deliberate practice of cultivating form constant imagery and using intuition or imagination to derive some meaning from transient visual phenomena.
Psychedelic art, inspired at least in part by psychedelic substances, frequently includes repetitive abstract forms and patterns similar to those created by paper marbling, and, in later years, fractals. The op art genre of visual art created art using bold imagery very like that of form constants.