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{{More citations needed|date=January 2022}}
{{short description|Recurringly observed geometric pattern}}
[[File:Form constant.jpg|right|thumb|300px|An example of a form constant
A '''form constant''' is one of several [[Pattern|geometric pattern]]s which are recurringly observed during [[hypnagogia]], [[hallucination]]s and [[altered states of consciousness]].
==History==
[[File:Klüver's Form Constants.jpg|thumb|Klüver's four form constants]]
In 1926, [[Heinrich Klüver]] systematically studied the effects of [[mescaline]] ([[peyote]]) on the [[subjective experience]]s of its users. In addition to producing hallucinations characterized by bright, "highly [[Saturation (color theory)|saturated]]" colors and vivid imagery, Klüver noticed that mescaline produced recurring [[geometric pattern]]s in different users. He called these patterns "form constants" and categorized four types: [[lattice (group)|lattices]] (including [[Hexagonal lattice|honeycomb]]s, [[checkerboard]]s, and [[triangle]]s), [[Spider web|cobweb]]s, tunnels, and [[spiral]]s.<ref name="Bressloff2002">{{cite journal | last =
In 1988 [[David Lewis-Williams]] and T.A. Dowson incorporated the form constant into his [[Entoptic phenomena (archaeology)#David Lewis-Williams's system|Three Stages of Trance model]], the geometric shapes comprising the visuals observed in the model's first stage.
==Precipitants==
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 experience]]s and sensory experiences of those with [[synesthesia]]. Other triggers include [[psychological stress]], [[hypnagogia|threshold consciousness (hypnagogia)]], [[insulin hypoglycemia]], the delirium of [[fever]], [[epilepsy]], [[psychosis|psychotic episodes]], advanced [[syphilis]], [[sensory deprivation]], [[photostimulation]], [[electrical stimulation]], [[crystal gazing]], migraine headaches, [[dizziness]] and a variety of [[drug]]-induced [[Substance intoxication|intoxication]]s.<ref name="Bressloff2002" /> These shapes may appear on their own or with eyes shut in the form of [[phosphene]]s, especially when exerting pressure against the closed eyelid.<ref>{{cite journal|last1=Tyler|first1=CW|title=Some new entoptic phenomena.|journal=Vision Research|date=1978|volume=18|issue=12|pages=1633–9|doi=10.1016/0042-6989(78)90255-9|pmid=726316|s2cid=30888279 }}</ref>▼
It is believed that the reason why these form constants appear has to do with the way the visual system is organized, and in particular in the mapping between patterns on the [[
▲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 experience]]s and sensory experiences of those with [[synesthesia]]. Other triggers include [[psychological stress]], [[hypnagogia|threshold consciousness (hypnagogia)]], [[insulin hypoglycemia]], the delirium of [[fever]], [[epilepsy]], [[psychosis|psychotic episodes]], advanced [[syphilis]], [[sensory deprivation]], [[photostimulation]], [[electrical stimulation]], [[crystal gazing]], migraine headaches, [[dizziness]] and a variety of [[drug]]-induced [[Substance intoxication|intoxication]]s.<ref name="Bressloff2002" /> These shapes may appear on their own or with eyes shut in the form of [[phosphene]]s, especially when exerting pressure against the closed eyelid.<ref>{{cite journal|last1=Tyler|first1=CW|title=Some new entoptic phenomena.|journal=Vision Research|date=1978|volume=18|issue=12|pages=1633–9|doi=10.1016/0042-6989(78)90255-9|pmid=726316}}</ref>
▲It is believed that the reason why these form constants appear has to do with the way the visual system is organized, and in particular in the mapping between patterns on the [[Retina|retina]] and the columnar organization of the [[Visual_cortex#Primary_visual_cortex_(V1)|primary visual cortex]]. Concentric circles in the retina are mapped into parallel lines in the visual cortex. Spirals, tunnels, lattices and cobwebs map into lines in different directions. This means that if activation spreads in straight lines within the visual cortex, the experience is equivalent to looking at actual form constants.<ref name="Bressloff2002" />
Author [[Michael Moorcock]] once observed in print that the shapes he had seen during his [[migraine headache]]s resembled exactly the form of [[fractal]]s. The diversity of conditions that provoke such patterns suggests that form constants reflect some fundamental property of [[visual perception]].
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==Cultural significance==
Form constants have a relationship to some forms of [[abstract art]], especially the [[visual music]] tradition, as [[William Wees]] noted in his book ''Light Moving in Time'' about research done by German psychologist Heinrich Klüver on the form constants resulting from mescaline intoxication. The visual and synaesthetic hallucinations this drug produced resembles, as Wees noted, a listing of visual forms employed in visual music:
{{blockquote|[Klüver’s] analysis of hallucinatory phenomena appearing chiefly during the first stages of mescaline intoxication yielded the following form constants: [emphasis original] (a) grating, lattice, fretwork, filigree, honeycomb, or chessboard; (b) cobweb; (c) tunnel, funnel, alley, cone or vessel; (d) spiral. Many phenomena are, on close examination, nothing but modifications and transformations of these basic forms. The tendency towards "geometrization," as expressed in these form constants, is also apparent in the following two ways: (a) the forms are frequently repeated, combined, or elaborated into ornamental designs and mosaics of various kinds; (b) the elements constituting these forms, such as squares in the chessboard design, often have boundaries consisting of geometric forms.<ref>Wees, William C. Light Moving in Time: Studies in the Visual Aesthetics of Avant-Garde Film, (Berkeley: University of California Press, 1992), p. 66.</ref>}}
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