By now we should all know the term "form constants", it's history, and the idea sets that accompany it. This page gives a fairly good summary in a short read, so, give it a try.
In 1926, Heinrich Klüver undertook a groundbreaking series of experiments where he categorized the visual effects produced by mescaline. Various volunteers were recruited, peyote administered, reports taken, and results classified into categories. There were general perceptual effects, variations in color and distortions of shape. But the most interesting reports were consistent visual concepts he dubbed “form constants”. Across many volunteers and many sessions, all reported seeing visual patterns with similar structure.
They were classified into four main types: I) tunnels, II) spirals, III) lattices, and IV) cobwebs. For almost fifty years, these form constants were regarded as a strange mystery of visual perception, a seemingly unexplainable common human experience.
In 1979 Jack Cowan and G. Bard Ermentrout put forward a very interesting explanation, supported by a rigorous mathematical treatment. These visual effects are the result of specific noise patterns in the visual cortex, which are then transformed by the wiring between the brain and the eye to produce these unique shapes."