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What makes us have chills when we go to a haunted house?
Can dogs detect cancer?
Your senses send your brain messages. But what do those messages say? Find out how to interpret your senses and explore ways that technology is changing the way we experience the world around us.
Copyright © 2008 by Donna M. Jackson
All rights reserved. Except as permitted under the U.S. Copyright Act of 1976, no part of this publication may be reproduced, distributed, or transmitted in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.
Little, Brown Books for Young Readers
Hachette Book Group USA
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Visit our Web site at www.HachetteBookGroupUSA.com
First eBook Edition: September 2008
Many generous people worldwide have shared their experiences, expertise, and images for this book. My heartfelt thanks to the following for thoughtfully taking time to tell their stories and conveying their knowledge in words and pictures: Dr. Jonathan Cole, Ian Waterman, Dr. A. James Hudspeth, Dr. Vilayanur Ramachandran, Carol Crane, Sean Day, Dr. Richard Cytowic, Edward Hubbard, Julia Simner, Esref Armagan, Joan Eroncel, John M. Kennedy, Dr. Alvaro Pascual-Leone, Pat Fletcher, Peter Meijer, Linda Muszynski, Tom Whittaker, Cheryl Schiltz, Yuri Danilov, Dr. Anil Raj, Karl Sigman, Hollis Long, Josh Tenenbaum, Sam Gosling, Thomas Gilovich, David G. Myers, Richard Wiseman, Ronald Rensink, Annette Martin, Athena Drewes, John Palmer, Rita Dwyer, Robert Van de Castle, Rosalind Cartwright, Caitlin O'Connell-Rodwell, Bill Barklow, Michelle Heupel, John Caprio, Debbie Marvit-McGlothin, Nicholas Broffman, Kathy Hill, Edith Resnick, Jep Enck, Gail Bishop, Lydia Kibiuk, Andy Manis, Matthew Wilson, Richard Masland, Rebecca Harkin, Tracey Somers, Anthony Freeman, David Simpson, Slawomir Grünberg, Zafer Kizilkaya, Dianne Patterson, Linda Briscoe, Cathy Strange, Eric Chudler, Shelley and Lauren Frihauf, Elif Ozdemir, Barbara Schweizer, David E. Simpson, Zafer Kizikaya, Cindy VanHorn, Brandi Dean, Yvette Reyes, Sona Walters and Ashley Morton.
A special thanks to Megan Tingley and Nancy Conescu at Little, Brown for sensing the book's potential; Tracy Shaw for her "phenomenal" design; Lauren Hodge for her editorial assistance; and to Charlie Jackson, whose love and support echo through the pages.
SENSING THE WORLD
I an Waterman of England seldom thought twice about his senses. Like most people, he took them for granted. That is, until age nineteen, when a flulike viral infection sapped his sensations from below the neck. "I just fell in a crumpled heap," he says. "Like a puppet with no strings."
A few days later, Ian was hospitalized. But instead of getting better, his condition deteriorated. "My first night in the hospital seemed to be the ebbing away of all that was normal in relationship to movement," he says. "I'd become sort of disembodied. . . . You know, I was a head without a body. I had no control over what was normally under my jurisdiction." Doctors didn't seem to have any answers either. That really scared him. After weeks of physical therapy, he says, "It became fairly clear nothing was happening."
Turns out, Ian suffered from a rare illness that stole his body's unconscious awareness of itself and its movable parts. Ian was "floppy" and lived in a "limbless limbo," says neurophysiologist Dr. Jonathan Cole. "Not only couldn't he feel anything to touch, he had no idea where the various bits of his body were without looking at them." Ian could move, he just couldn't instinctively control or coordinate those movements because his brain wasn't receiving sensory feedback to help him monitor his actions. Communication between his brain and body had broken down.
Through the years and against all odds, Ian trained himself to carefully choreograph each movement he made using vision as his guide. "Once you realize the damage is done, you get on with it," he says. By looking at his limbs and concentrating on making his body move, Ian eventually learned to sit up, stand, and drive a car. "I became the ultimate control freak," he says. Of the ten known people in the world with this condition, Ian's believed to be the only one who has taught himself to walk.
At age nineteen, Ian Waterman lost his sense of proprioception—the body's unconscious awareness of itself and its movable parts.
Photo courtesy of Ian Waterman
Our senses help us navigate the world. Working in concert, they feed important information to the brain about what's happening to, and around, our bodies. The simplest of acts — such as recognizing and waving hello to a friend — require hundreds of millions of sensory nerve cells, called neurons, to communicate with the brain so that we can instantly read and react to situations.
While the primary five senses — vision, hearing, touch, taste, and smell — are most obvious, at least twenty-one have been identified. We have a sense of hunger, thirst, balance, and fatigue. We sense pain, temperature, and muscle tension. We even have senses that detect pressure in our gut and bladder, as well as those that adjust our heartbeat and measure the levels of oxygen and carbon dioxide in our blood. These senses keep the body running smoothly.
Our senses help us consciously create and experience the world. They bring us pleasure: tender touches, sparkling skies, and the rhythmic rhapsodies of music. They alert us to dangers: screeching tires, a flash of lightning, and the pungent odor of natural gas. Our senses also enable us to distinguish sweet from sour, hot from cold, and light from dark.
Our senses help us experience the world and often bring us pleasure.
© Blend Images
Even before we're born, sensations offer us a window to the world. Our sense of touch begins developing at about eight weeks after conception. Soon we're sucking our thumbs and exploring our faces with our fingers. By about eighteen weeks, we hear our mother's breathing and the tha-thump, tha-thump of her heartbeat. This calming cadence appears in other areas of our lives, notes Jillyn Smith in her book Senses and Sensibilities. "It has been suggested that children begin to speak in double syllables — da-da, ma-ma — in imitation of the paired heartbeat sounds, and that a child instinctively clings to the left side, the heartbeat side, of the mother's breast."
See an X made of circles that pop out? It's an optical illusion. Our brains sense that light shines from above, so the circles that are shaded lighter on top seem to stand out, while those that are shaded darker on top recede. Turn the page upside down and watch what happens.
Mark R. Holmes, © National Geographic Society
Yet while we all live in the same physical world, each of us experiences it uniquely, says psychologist and professor Francis B. Colavita of the University of Pittsburgh. Not only do our senses respond to different elements in the environment, our brains assign different meanings to the same sensations. "A perception is a sensation plus its unique meaning for an individual," explains Colavita. "Two people may be exposed to the same sensory (information), but their differing personalities, cultural backgrounds, expectations, motivational and emotional states, family histories, and life experiences will determine how similar or different their perceptions of that sensory [information] will be." A person who's recently been in a car accident, for example, is more apt to flinch when an ambulance races by than someone who hasn't suffered the same trauma.
Individually, we also experience different "realities" throughout our lifetimes as we continually grow and develop. Our sensory systems age and evolve along with us, says Colavita, so what tasted great at seven may not be so appetizing at seventy.
DECIPHERING THE BIG PICTURE
One major mystery of neuroscience is how the brain, which contains about 100 billion nerve cells, processes all the sensory signals it receives in fragments and unifies them as a whole into our overall perceptions. Scientists refer to this as "the binding problem."
Our brains contain billions of nerve cells, or neurons, that constantly communicate with each other via electrical signals. Different neurons hold different jobs. Some help coordinate muscle movements, while others take in messages from our senses.
Courtesy of the Alzheimer's Disease Education and Referral (ADEAR) Center
Visual images, for example, may be parallel-processed in twenty-five or more regions of the brain, each with a specialized job such as color identification, depth perception, and motion detection. "Yet somehow the brain pulls it back together," says Dr. A. James Hudspeth, a researcher for the Howard Hughes Medical Institute and head of the Laboratory of Sensory Neuroscience at the Rockefeller University in New York. "In addition to seeing the particular color of your skin and hair and the particular outlines of your face and how far away you are, and whether or not you're moving and so on, I'm able to see all the pieces together and identify you."
Always at work, our brains make educated guesses that fill in the blanks where needed. That's why you see triangles in the above image.
Mark R. Holmes, © National Geographic Society
And that's just one sense. Factor in messages flooding in from what you're hearing, smelling, and touching — along with inputs from your memories, previous experiences, and the context of the situation — and the brain's making multifaceted connections and shaping perceptions with astonishing speed and precision.
"We still don't know how this operates," says Dr. Hudspeth. "But it is known that beyond the simpler parts of the cerebral cortex, there are a number of association areas that are sensitive to more than one sense at the same time. So they may be excited by sound or by a visual stimulus or by touch simultaneously." This leads to the theory that the association cortex, which is involved in higher processing of information, is responsible somehow for pulling together our perceptions.
"One of our most striking senses is equilibrium or balance," says Dr. A. James Hudspeth, a researcher for the Howard Hughes Medical Institute. "Our capacity to stand upright, for example, depends critically on feedback from the inner ear—the vestibular labyrinth—which constantly measures our body's position and whether it's beginning to fall one way or another."
© AP Wide World Photos
Emotions also influence our perceptions of the world. Seeing a close friend or relative generally elicits a myriad of feelings associated with that person. After we've identified someone visually, for example, the message moves to the amygdala, an area of the brain that helps us determine a person's emotional significance.
People with Capras syndrome, however, lose this emotional connection. This rare neurological condition — often the result of a severe head injury — appears to damage the neural pathways between the visual and emotional centers of the brain, explains Dr. Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego. As a result, those afflicted believe the people closest to them are imposters.
One man injured in a car accident thought his mother was an imposter. "Doctor, this woman looks exactly like my mother but she isn't," he insisted. Since the man didn't feel appropriate emotions when he saw his mother, he decided she must be someone pretending to be her. When the man's mother telephoned him an hour later, however, he immediately recognized her and her voice. Apparently, the auditory path to the emotional center had remained intact.
Conditions such as Capras syndrome offer scientists an opportunity to learn more about the workings of the brain. They also offer compelling examples of how our perceptions are not only shaped by the sensory information we receive, but by how the information is processed and interpreted in the brain.
Our senses hold many secrets, and questions abound about the extent of their capabilities. Many unexplained phenomena, for instance, have roots in our sensations and the way the brain understands them through our perceptions.
- On Sale
- Sep 1, 2008
- Page Count
- 192 pages
- Little, Brown Books for Young Readers