Jim Collins and colleagues at Boston University wondered if such people could benefit from "stochastic resonance" - an effect that makes a weak signal easier to detect when it is superimposed on a background of random noise. The team built a randomly vibrating platform, and asked volunteers to stand on it. They hoped the vibrations would amplify the cues coming from people's feet and help them stay steady (see Graphic).
Sure enough, people swayed several millimetres less in each direction when the platform was gently vibrating, even though they couldn't consciously sense its movement. This is about the same as the difference between elderly volunteers and people in their twenties.
Increasing the information coming from the soles of the feet helps to improve balance control, concludes Collins, who has submitted the finding to Physical Review Letters. The nervous system soon learns to ignore regular signals, so the technique only works if the information coming in is genuine noise.
Other researchers have suggested that the nervous system generates its own noise to help with tasks such as balancing a stick on the end of the fingertips (New Scientist, 5 October, p 19). But Collins's group is the first to show that artificially adding random signals can boost balance.
Collins now hopes to develop a vibrating insole that unstable walkers could wear in their shoes. But he hasn't yet worked out how to power them efficiently without heavy battery packs.
Neurologist John Milton of the University of Chicago says trials are needed to show that swaying less does help people stay on their feet. But he believes such insoles could help people who have already fallen. "It might give them the confidence to get walking again."
Author: Eugenie Samuel, Boston
New Scientist issue: 2nd November 2002
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