retinal shadow
   The term retinal shadow is indebted to the Latin noun retina (little net). It is used to denote a " pseudentoptic phenomenon which is characterized by an inverted retinal image. A retinal shadow can be evoked experimentally by holding a pin upright, very close to the eye, while it is illuminated from behind by a beam of light that shines through a pinhole into the eye. The pin's shadow will then be projected upside down on the retina, with fuzzy edges, conjuring up the " illusion that the pin itself is in an upside-down position.
   References
   Johannsen, D.E. (1971). Early history of perceptual illusions. Journal of the History of the Behavioral Sciences, 7, 127-140.

Dictionary of Hallucinations. . 2010.

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