When you stare at the cross for at least 30 seconds, you see three illusions:
• A gap running around the circle of lilac discs;
• A green disc running around the circle of lilac discs in place of the gap; and
• The green disc running around on the grey background, with the lilac discs having disappeared in sequence. — Lilac Chaser, Wikipedia
Elsewhere Other-Accessible…
• Troxler’s fading at Wikipedia
Chimerical colors (from Wikipedia)
(click for larger)
Use a straight-edged object against the screen to confirm that these are straight lines
Perfect circles, despite what your eyes say
Concentric circles, not a spiral
The optical illusions above are by the Japanese psychologist Akiyoshi Kitaoka via SYFY.
Cats are of divers colours, but for the most part griseld, like to congealed ise, which cometh from the condition of her meat: her head is like unto the head of a Lion, except in her sharp ears: her flesh is soft and smooth: her eyes glister above measure, especially when a man cometh to see them on the suddain, and in the night they can hardly be endured, for their flaming aspect. Wherefore Democritus describing the Persian Smaragde saith that it is not transparent, but filleth the eye with pleasant brightness, such as is in the eyes of Panthers and Cats, for they cast forth beams in the shadow and darkness, but in sunshine they have no such clearness, and thereof Alexander Aphrodise giveth this reason, both for the sight of Cats and Bats, that they have by nature a most sharpe spirit of seeing. — Edward Topsell, Historie of Foure-Footed Beastes (1658).
Eye Bogglers: A Mesmerizing Mass of Amazing Illusions, Gianni A. Sarcone and Marie-Jo Waeber (Carlton Books 2011; paperback 2013)
A simple book with some complex illusions. It’s aimed at children but scientists have spent decades understanding how certain arrangements of colour and line fool the eye so powerfully. I particularly like the black-and-white tiger set below a patch of blue on page 60. Stare at the blue “for 15 seconds”, then look quickly at a tiny cross set between the tiger’s eyes and the killer turns colour.
So what’s not there appears to be there, just as, elsewhere, what’s there appears not to be. Straight lines seem curved; large figures seem small; the same colour seems light on the right, dark on the left. There are also some impossible figures, as made famous by M.C. Escher and now studied seriously by geometricians, but the only true art here is a “Face of Fruits” by Arcimboldo. The rest is artful, not art, but it’s interesting to think what Escher might have made of some of the ideas here. Mind is mechanism; mechanism can be fooled. Optical illusions are the most compelling examples, because vision is the most powerful of our senses, but the lesson you learn here is applicable everywhere. This book fools you for fun; others try to fool you for profit. Caveat spectator.
Simple but complex: The café wall illusion
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