These are the images which are examined by J D Lewis-Williams and T A Dowson (1988) and Richard Bradley (1989)
These are the entoptic images which are examined by J D Lewis-Williams and T A Dowson in their 1988 article "The Signs of All Times". They postulate that these images, which derive from effects within the central nervous system, form the basis for images in Palæolithic art.
The images above each other, with the lower slightly to the right of the upper if your browser window is wide, are equivalent effects from the two sources. One important form, the spiral, is not shown since it is for some reason omitted from consideration by Lewis-Williams and Dowson and their example was followed by Richard Bradley.
Bradley cites the same figures in his 1989 article, "Deaths and entrances: A contextual analysis of megalithic art", in which he supports Lewis-Williams and Dowson with evidence from "Megalithic" (Neolithic) tombs in southern Brittany.
These works have received criticism for the sheer breadth of their arguments. Many commentators feel that evidence is being stretched beyond its limits in order to fit an "all-encompassing theory" which may not be valid. However, there is good reason to suppose that some of these elements are derived from entoptic phenomena. Bradley makes a very good case for some of the patterns at Newgrange in Ireland and, more particularly, for some of the stones in the temple-tomb at Gavrinis, Brittany.
Some of the stones at Gavrinis were re-used; new decoration was added which avoided obliterating the older images. The Gavrinis patterns are reminiscent of rock engravings from Australia and South-West America, which might indicate some "universal" experience on the part of the makers. The images also fit well with the "entoptic phenomena" theory.
Other commentators have suggested that the Gavrinis patterns are indicative of a universal "Mother-Goddess" religion. The evidence for such universality is relatively weak and it's more probable that several local cults were involved. However, an entoptic origin for the images is not completely inconsistent with their being part of Goddess worship; construal of the images is what would give them meaning to their makers.
Equally, most commentators would agree that Hildgard of Bingen was a migraine sufferer. It's possible to see entoptic imagery in some of the illuminations for her work, particularly the bright and dark stars, and corona-catenary effects in her visions of "Anima". But as at Gavrinis, the construal stage is what gives the visions meaning and a migraine origin of the images does not affect the question of validity of the resulting visions.The word "Entoptic" was coined for these phenomena by C W Tyler, a researcher into vision, and appears in the title of his 1978 paper "Some New Entoptic Phenomena" in Vision Research 18: 1633-39. Lewis-Williams, "hoping to avoid a diversionary logomachy", used the term instead of "phosphenes".
Interest in these visual precepts stems from the late 19th Century, but the original laboratory work from which these images are drawn was by Heinrich Klüver in the 1920s. He published a paper, "Mescal Visions and Eidetic Vision" in 1926. This work was independently repeated by M J Horowitz "The Imagery of Visual Hallucinations", 1964.
The works upon which Lewis-Williams and Dowson chiefly draw are those of R K Siegel and W Richards. Siegel's work, with cocaine, is described in "Hallucinations", Scientific American, 237, 132-40. Richards' work appears in "The Fortification Illusions of Migraine", Scientific American, 224:89-94.
The images are generated in reaction to various stresses on the body, including migraine, extreme fatigue or being hit on the back of the head with a frozen halibut. However, most of the research derives from laboratory work with hallucinogenic drugs. Generation of the images passes through three stages, involving seven principles:
Seven Principles of Perception
Despite the varied nature of entoptic and iconic hallucination, Lewis-Williams and Dowson formulate seven principles of perception; although defined with reference to entoptics, these principles also apply to iconic hallucinations
Lewis-Williams and Dowson finally define three stages in the progression of mental imagery during states of consciousness in which entoptic phenomena are experienced:
In stage one, subjects experience entoptic phenomena alone. These can be perceived either with the eyes open or closed and tend to be located at reading distance. The images cannot be consciously controlled and are characterised by varied and saturated colours. Sometimes a bright light obscures all but peripheral images.
In stage two subjects try to make sense of entoptics by elaborating them into iconic forms. Thus, the same ambiguous round shape can be 'illusioned' into an orange if the subject is hungry, or a breast if he is in a state of heightened sexual drive.
In stage three many subjects experience a vortex or rotating tunnel that seems to surround them. There is a progressive exclusion of perceptual information. Iconic images appear to derive from memory and are often associated with powerful emotional experiences. Subjects tend to assert that the images are actually what they seem to be, without discrimination between the phenomenon and the construed object.