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The Neuroscience of
Illusion May 28, 2008 How tricking the eye reveals the inner workings of the brain Brightness and Color Illusions http://tinyurl.com/67uffr - - - In this illusion, created by Edward Adelson at MIT, squares A and B are the same shade of gray. http://tinyurl.com/52k324  (If you don't believe it, print it out and then cut out the two squares and place them side by side.) This illusion occurs because our brain does not directly perceive the true colors and brightness of objects in the world, but instead compares the color and brightness of a given item with others in its vicinity. For instance, the same gray square will look lighter when surrounded by black than when it is surrounded by white. - - - May 28, 2008 How tricking the eye reveals the inner workings of the brain Shape Distortion Illusion http://tinyurl.com/6dl2fb - - - This illusion is known as the Cafe Wall illusion, and it was first discovered by Richard Gregory's laboratory in a cafe in Bristol, in the U.K. http://tinyurl.com/5du8cw  The black and white tiles are perfectly straight, but look tilted. It is a shape distortion illusion: an object will appear to take on shapes that are different from its actual shape. Like brightness and color illusions, shape distortion effects are also produced by the interaction between the actual shape of the object and the shapes of nearby figures. For the brain, perception is very often dependent on context. - - - May 28, 2008 How tricking the eye reveals the inner workings of the brain Illusory Motion http://tinyurl.com/64e372 - - - Some stationary patterns generate the illu- sory perception of motion. The illusory effect is usually stronger if you move your eyes around the figure. http://tinyurl.com/5l72u3  For instance, in this illusion, invented by the scientist Akiyoshi Kitaoka, the "snakes" appear to rotate. But nothing is really mov- ing, other than your eyes! If you hold your gaze steady on one of the black dots on the center of each "snake," the motion will slow down or even stop. Because holding the eyes still stops the illusory motion, we speculate that eye movements are required to see it. Vision scientists have shown that illusory motion activates brain areas that are similar to those activated by real motion. - - - May 28, 2008 How tricking the eye reveals the inner workings of the brain Ambiguous Figures http://tinyurl.com/5wjfja - - - This bunch of violets contains the faces of Napoleon, his wife, and their child. Can you find them among the flowers? http://tinyurl.com/5ojyg3  During Napoleon's exile, his supporters used to distribute reproductions of this 1815 en- gravings. In such illusions, the brain interprets same picture in two different ways, with each interpretation mutually exclusive of the other. You can see one of two possible images, but never both of them at the same time. These so-called ambiguous figures are especially powerful tools to dissociate the subjective perception from the physical world. The physical object never changes, yet our perception alternates between two (or more) possible interpretations. For this reason, am- biguous illusions are used by many labora- tories in the search for the neural correlates of consciousness. - - -
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