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updated 1/26/2011 11:16:26 AM ET 2011-01-26T16:16:26

Scientists may have found a clue as to why elderly people have trouble driving: They focus too much on the background of moving objects, and not enough on the actual moving objects in the foreground.

A heightened awareness of the people and cars moving in the background appears to distract their brains from what's happening right in front of them, new research suggests.

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"The amount of visual information around us is huge, and we don't have the brain power to process it all," study researcher Duje Tadin of the University of Rochester said in a statement.

In a healthy, young person, a brain region called the middle temporal visual area actively suppresses information about irrelevant background motion, allowing the person to concentrate on the more important motions of objects in the foreground, according to the study.

But elderly people — and people with certain psychological conditions such as schizophrenia and depression — are better at perceiving the motion in the background. Because the brain is constantly paying attention to the unimportant motions of background objects, it has a harder time noticing the motions of smaller objects, the study said.

Test used metal coils on subjects' heads
Tadin and his colleagues placed metal coils on the backs of the heads of six people, ages 22 to 32. The researchers used electrical signals to stimulate the middle temporal visual area of their brains for 15 minutes, to temporarily inhibit its functioning.

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The researchers then tested how well the participants identified motions of smaller and larger objects. They found that when the middle temporal region was inhibited, the people had an easier time identifying the motion of large, background-like objects.

These results show that an improperly functioning middle temporal visual area may be causing increased perception of background motion in older adults, according to the study.

This finding could be useful to psychiatrists in diagnosing schizophrenia and depression, Tadin said. They could test a person's ability to detect background motion compared to foreground motion.

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