If Granny has trouble keeping her equilibrium, it may be because her feet have become less sensitive to pressure changes. Boston scientists have found that they can diminish swaying in elderly people by sending subliminal, erratic vibrations to the bottoms of the seniors' feet. This subtle postural therapy relies on a principle known as stochastic resonance, whereby noise improves signal recognition in a system such as the nerves (SN: 11/23/96, p. 330).
Pressure changes on the bottom of feet normally signal that the standing body is beginning to sway–movement that can lead to falls in the elderly. To reduce swaying, James J. Collins of Boston University and his colleagues developed gel-based insoles embedded with battery-powered mechanical vibrators, called tactors. Then, they asked volunteers to stand shoeless on these cushions with their eyes closed for a series of 30-second tests–20 trials for people in their 20s and 10 trials for those in their mid-70s. During