An optical Illusion, illustrated above, in which the eye perceives a white upright Equilateral Triangle where none is actually drawn.
See also Illusion
References
Bradley, D. R. and Petry, H. M. ``Organizational Determinants of Subjective Contour.'' Amer. J. Psychology 90, 253-262, 1977.
Fineman, M. The Nature of Visual Illusion. New York: Dover, pp. 26, 137, and 156, 1996.