febrero 11, 2008

It's All in the Brain




Illusions Reveal the Brain's Assumptions.

By Maya Pines




We can recognize a friend instantly—full-face, in profile, or even by the back of his head. We can distinguish millions of shades of color, as well as 10,000 smells. We can feel a feather as it brushes our skin, hear the faint rustle of a leaf. It all seems so effortless: we open our eyes or ears and let the world stream in.


Yet anything we see, hear, feel, smell, or taste requires billions of nerve cells to flash urgent messages along cross-linked pathways and feedback loops in our brains, performing intricate calculations that scientists have only begun to decipher.


"You can think of sensory systems as little scientists that generate hypotheses about the world," says Anthony Movshon, an HHMI investigator at New York University. Where did that sound come from? What color is this, really? The brain makes an educated guess, based on the information at hand and on some simple assumptions,
says Vilayanur Ramachandran, a professor of neuroscience at the University of California, San Diego.


To resolve ambiguities and make sense of the world, the brain also creates shapes from incomplete data, Ramachandran says. He likes to show an apparent triangle that was developed by the Italian psychologist Gaetano Kanizsa (see right). If you hide part of this picture, depriving the brain of certain clues it uses to form conclusions, the large white triangle disappears.


We construct such images unconsciously and very rapidly. Our brains are just as fertile when we use our other senses. In moments of anxiety, for instance, we sometimes "hear things" that are not really there. But suppose a leopard approached, half-hidden in the jungle—then our ability to make patterns out of incomplete sights, sounds, or smells could save our lives.

http://www.hhmi.org/senses/a110.html

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