CHICAGO, Sept. 24 (UPI) -- By using high-speed infrared cameras to analyze the simple act of people balancing sticks on their fingertips, scientists have revealed unexpected insights into how the human nervous system deals with stability problems.
Surprising, but the nervous system introduces random motions into a person's finger and these motions help balance the sticks, researchers at the University of Chicago said.
The new findings about human balancing acts could help design everything from novel earthquake-proof buildings, two-legged walking robots and vibrating shoes to help the elderly keep from falling.
"Every movement is possible only with proper balance -- you can't walk if you're falling over all the time," neurologist John Milton told United Press International. "We're looking at the fundamentals at the basis of all movement."
Although balancing a stick on one's fingertip is one of the simplest experiments to test human balance, the act in many ways is similar to people balancing on their feet or buildings standing on their bases, Milton explained. It is hard balancing a short stick like a pen, but the longer the stick gets, the more slowly it tips over, giving the nervous system more time to make stabilizing corrections in arm motion.
Milton and physicist Juan Cabrera of the Venezuelan Institute for Scientific Research in Caracas decided to study how the nervous system compensates for the time delays required for nerve impulses to travel to and from the brain -- "the time between when the light turns green and when you move the car by stepping on the gas," Milton said.
They used infrared cameras in their experiments that could record at up to 1,000 frames per second, picking up details one to 10 microns in size, or a tenth to a hundredth the width of a human hair. The sticks had mirror balls at their tips that reflected the infrared light the cameras emitted and measured.
Milton and Cabrera said they thought the experiment would be relatively simple, but it took more than two years to complete. "People ask you what you've been doing for the last few years, and when you say you're doing stick balancing, this look comes over their eyes," Milton said.
Their early results startled them enough to press on, however. There is a delay of 100-to-200 milliseconds between when the brain perceives the stick is tipping over and when it reacts. Yet, "98 percent of the corrective movements to keep the stick balanced happened faster than the time delay," Milton said. In other words, the reactive movements were happening faster than physically possible. "That's pretty unusual," he said.
Using mathematical analysis of the stick's motions, Milton and Cabrera discovered lots of random arm motions were involved. Most surprising, the stick did not stay balanced despite of such wavering, but because of it. The instability added by the fast and random fluctuations, or "noise," makes the finger more maneuverable and aids in balance, a strategy similar to that employed in designing advanced fighter aircraft.
"The noise pushes balancing to the boundary between stability and instability," Milton said.
The scientists said they still are not sure what causes the motion noise. They could be due simply to random alterations in nerve conductivity or body temperature levels, or there could be a "noisemaker" somewhere that intentionally adds random motions, Milton said.
"They've found all kinds of interesting things in what looks fairly simple," Sue Ann Campbell, an applied mathematician with the University of Waterloo in Ontario, told United Press International. Research still needs to prove these findings can generalize to the rest of the body, she added, but "they've come up with a nice model that shows a good idea of what the nervous system may be doing."
Milton and Cabrera will publish their findings in the Oct. 7 issue of Physical Review Letters.
(Reported by Charles Choi, UPI Science News, in New York)