mosaic vision

   Also known as mosaic illusion and geometrizating illusion. The term mosaic vision was introduced in or shortly before 1970 by the British neurologist Oliver Wolf Sacks (b. 1933) to denote a visual distortion characterized by the fragmentation of perceived objects into irregular, crystalline, polygonal facets, interlaced as in a mosaic. These facets can take on various sizes and forms, typically covering the whole field of vision. As Sacks observes, "The size of the facets may vary greatly. If they are extremely fine, the visual world presents an appearance of crystalline iridescence or 'graininess,' reminiscent of a pointillist painting. If the facets become larger, the visual image takes on the appearance of a classical mosaic, or even a 'cubist' appearance. If they compete in size with the total visual image, the latter becomes impossible of recognition, and a peculiar form of visual agnosia is experienced." It is also noted by Sacks that "typically there is movement - a continual changing of scales - and often, simultaneously, an admixture of several scales". Eti-ologically, mosaic vision is associated primarily with * aurae occurring in the context of paroxysmal neurological disorders such as migraine and epilepsy. The pathophysiology of mosaic vision is basically unknown. However, it has been suggested that it may share certain mechanisms of activation of visual representation with those involved in the mediation of *geometric hallucinations. Mosaic vision is commonly classified as a * metamorphopsia, which is itself classified as a * sensory distortion. The notion of mosaic vision should not be confused with the notion of * tessellopsia.

   References

   Podoll, K., Robinson, D. (2000). Mosaic illusion as visual aura symptom in migraine. Neurology, Psychiatry and Brain Research, 8,181-184. Sacks, O. (1992). Migraine. Revised and expanded. New York, NY: Vintage Books.