photically induced hallucination

   Also known as flicker-induced hallucination, hallucinatory flicker-induced experiences, and Purkinje's colours. All four terms are used to denote a type of *geometric visual hallucination induced by a flickering light, such as that produced by a stroboscope or by sunlight interrupted by the shadows of trees, as observed by an individual moving along those trees. Phenomeno-logically, photically induced hallucinations may resemble the geometric * form-constants as described by the German-American biological psychologist and philosopher Heinrich Klüver (1897-1979). Under laboratory conditions many different shapes have been reported, including *gratings, * spirals, concentric circles, and fan blades. However, contrary to the hallucinogen-induced hallucinations described by Klüver, photically induced hallucinations tend to lack an extreme saturation of colour. The mediation of the geometric forms is attributed to stripe patterns of neural activity in specialized cortical columns whose spatial orientation on the visual cortex combines with a nonlinear retinocortical mapping. Photically induced hallucinations were probably described for the first time in 1819 by the Bohemian physiologist Johannes Evangelista Purkyne (1787-1869). A special type of the photically induced hallucination is the *television-induced hallucination.

   References

   Billock, V.A., Tsou, B.H. (2007). Neural interactions between flicker-induced self-organized visual hallucinations and physical stimuli. Proceedings of the National Academy of Sciences of the United States of America, 104, 8490-8495.