Soldiers confronting brown-out conditions from desert dust in Iraq are coping with a swirl of confusing sensory input not unlike that experienced by many ordinary people in everyday life. How our senses – what we hear, what we see and feel and so on – work together to enable us to survive is the purview of a University of Rochester neuroscientist who has found that our brain’s ability to cope with a hodgepodge of mixed signals is even more robust than scientists have thought.
Anyone who has put on a new pair of eyeglasses knows how different and confusing the world can suddenly appear. Abruptly the world just looks different, and our brain has to adapt. Making sense of such information is crucial for soldiers caught up in sandstorms, for the elderly as they age and become more prone to falling, and for pilots guiding their aircraft off a carrier deck in the black of night or in bad weather. The whirl of conflicting information can make it impossible to distinguish “down” from “up” and can send an inexperienced pilot to his or her death.
Recently, Gary Paige, M.D., Ph.D., conducted a sort of pop quiz to check the brain’s ability to cope with an onslaught of unexpected sensory information. He outfitted 10 people with experimental goggles that severely skewed their vision of the world, then measured how they adapted. Instead of seeing things as they normally appear, the participants wore goggles with wide-angle lenses that squeezed a wider scene than they’d usually see into their field of view. The effect, according to participant Owen Brimijoin, “was like looking through an apartment keyhole – straight lines were curved, and everything was smaller.”
For two days Brimijoin and his counterparts went through their daily routines wearing the glasses, bumping into walls and doorways and drawing some odd looks at restaurants and at the office. While their vision was distorted by the goggles, the participants’ hearing hadn’t been tampered with, resulting in a mismatch in which they appeared to hear sounds from places other than the source. For instance, sometimes when they looked at a person who was talking, the person’s voice sounded like it came from an unseen area off to the left.
The brain adapted very well to the sudden shift: Despite the conflicting information from their senses, people gradually learned to match the sound with the image. Paige presented the work at a recent meeting of the Association for Research in Otolaryngology and reported the results in the February issue of Nature Neuroscience. The work by Paige and his colleagues, Marcel P. Zwiers and A. John Van Opstal of the University of Nijmegen in the Netherlands, was funded by the National Institutes of Health (NIH) and the Human Frontiers Science Program.
“This is about the evolution of our ability to get around and avoid hurting or killing ourselves,” says Paige, professor and chair of the Department of Neurobiology and Anatomy. “For instance, if you’re walking through a busy intersection and someone honks at you, you have to identify the correct car by the source of the sound. You can’t really tell just by looking at all the cars. It’s up to you and your brain to link what you hear with what you see.
“You wouldn’t be able to survive without your senses working together. When your senses don’t work together correctly, bad things happen.”
Brimijoin experienced this first-hand, when he became quite nauseous from wearing the makeshift goggles. But by the end of the second day he had adjusted to the distortions.
“It was very disorienting – there was more stuff squished into my visual field, and all of it was smaller,” says Brimijoin. “I was worthless at first, but by the end of the first day, I had the whole ‘walking thing’ down. It took awhile to readjust: When someone would speak, it sounded like the voice was coming out of nowhere, even though I could see the person’s mouth moving.” But within two days, Brimijoin’s brain had adapted, and the information from his senses once again made sense.
When information from our senses doesn’t match up, motion sickness like Brimijoin experienced is a common side effect, Paige says. It happens when the information coming from our better-known senses, vision and hearing, does not match up with data coming from a lesser-known sense called the vestibular system, a labyrinth of tiny structures in the inner ear that measure our own motion, and gravity, to help us keep our balance. The system also makes the world appear stable and steady even though we are constantly on the move, helping us to know whether we or the things around us are moving.
“It’s a miraculous system that is essential to normal active life,” says Paige. “People without a vestibular system live in a world of bad home movies.
“Sometimes the vestibular system plays tricks on us. We lose pilots every year because of vestibular illusions – it can be impossible to distinguish what angle you’re flying at or from what rate you’re accelerating through a dark sky over the desert. The pilots must rely on instruments. If their instruments break, or they ignore them, they can end up in the drink,” says Paige.
Problems with the vestibular system will ultimately confront nearly all of us: By the time a person reaches his or her 80s, nearly half the vestibular system has simply degenerated, causing problems with balance and dizziness. Other people are affected when they have a stroke or an inner-ear problem. It’s one reason why millions of elderly people fall every year, often resulting in a dramatically worsened quality of life.
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