In the above illustration, black dots appear to form and vanish at the intersections of the gray horizontal and vertical lines. When focusing attention on a single white
dot, some gray dots nearby and some black dots a little further away also seem to
appear. More black dots seem to appear as the eye is scanned across the image (as
opposed to focusing on a single point). Strangely, the effect seems to be reduced,
but not eliminated, when the head is cocked at a angle. The effect seems to exist only at intermediate
distances; if the eye is moved very close to or very far away from the figure, the
phantom black dots do not appear.
The illusion is known as the scintillating grid, and was discovered by E. Lingelbach in 1994. It is a modification of the Hermann
grid illusion.
Gephart, J. "Find the Black Dot." http://udel.edu/~jgephart/fun2.htm.Lingelbach, B. and Ehrenstein, W. H. Jr. "Das Hermann-Gitter und die Folgen."
http://www.leinroden.de/304herfold.htm.Lloyd,
S. J.-A. "How Has the Hermann Grid Been Useful in Exploring Human Vision?"
http://web.mit.edu/sjlloyd/www/Perception/table.html.Schrauf,
M.; Lingelbach, B.; Lingelbach, E.; and Wist, E. R. "The Hermann Grid and
the Scintillation Effect." Perception24, suppl. A, 88-89, 1995.Schrauf,
M.; Lingelbach, B.; and Wist, E. R. "The Scintillating Grid Illusion."
Vision Res.37, 1033-1038, 1997.Seckel, A. The
Art of Optical Illusions. Carlton Books, p. 12, 2002.
angle. The effect seems to exist only at intermediate
distances; if the eye is moved very close to or very far away from the figure, the
phantom black dots do not appear.
