Today's selection -- from The Body by Bill Bryson. The fallibility of memory and perception:
"Your brain is also extraordinarily good at finding patterns and determining order in chaos, as these two well-known illusions show:
"In the first illustration, most people see only random smudges until it is pointed out to them that the picture contains a dalmatian dog; then suddenly for nearly everyone the brain fills in the missing edges and makes sense of the whole composition. The illusion dates from the 1960s, but no one seems to have kept a record of who first created it.
"The second illustration does have a known history. It is called a Kanizsa triangle, after the Italian psychologist Gaetano Kanizsa, who created it in 1955. There is of course no actual triangle in the picture, except for the one your brain puts there.
"Your brain does all these things for you because it is designed to help you in every way it can. Yet paradoxically it is also strikingly unreliable. Some years ago, a psychologist at the University of California at Irvine, Elizabeth Loftus, discovered that it is possible through suggestion to implant entirely false memories in people's heads -- to convince them that they were traumatically lost in a department store or shopping mall when they were small or that they were hugged by Bugs Bunny at Disneyland -- even though these things never happened. (Bugs Bunny is not a Disney character and has never been at Disneyland.) She could show many people pictures of themselves as a child in which the image had been manipulated to make them look as if they were in a hot-air balloon, and often the subjects would suddenly remember the experience and excitedly describe it, even though in each case it was known that it had never happened.
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The story does not have a Kanizsa Triangle so here's an example from The Illusions Index:
Description:
A symmetrical figure consisting of 3 discs each missing a triangular section, and 3 pairs of lines.
Instructions
What shapes do you experience in the figure? What shapes are there in the figure?
Effect
The figure is often experienced as a solid triangle pointing upwards that is lighter than the background, which occludes an inverted triangle pointing downwards, and a set of black discs which are also occluded by the solid bright white triangle that points upwards. Surprisingly, none of these shapes are actually present in the figure....
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