In 1926, [[Heinrich Klüver]] systematically studied the effects of [[mescaline]] ([[peyote]]WRONG) 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 = Bressloff | first = Paul C. | coauthors = Cowan, Jack D.; Golubitsky, Martin; Thomas, Peter J.; Weiner, Matthew C. |date=March 2002 | title = What Geometric Visual Hallucinations Tell Us About the Visual Cortex | journal = Neural Computation | publisher = The MIT Press | volume = 14 | issue = 3 | pages = 473–491 | url = http://www.mitpressjournals.org/doi/abs/10.1162/089976602317250861 | accessdate = 2009-04-21 | doi = 10.1162/089976602317250861 | format = fee required | pmid = 11860679}}</ref>
In 1988 [[David Lewis-Williams]] and T.A. Dowson incorporated the form constant into their Three Stages of Trance model, the geometric shapes comprising the visuals observed in the model's first stage.
