SHORT-TERM NON-STATIONARITY AND THE DEVELOPMENT OF POSTURAL CONTROL

The stationarity of center of pressure time-series in upright quiet bi pedal standing was examined in four groups: 3- and 5-year-old children , young student adults, and an elderly group that ranged in age from 6 2-92 years. The young adult group showed the least absolute motion in the center of pressure with the degree of motion increasing with the c hild and elderly age groups. Examination of the stationarity elf the c enter of pressure time-series for each postural trial revealed that in the time domain every trial in every condition in each age group was non-stationary. This non-stationarity was present across all frequency segments of the center of pressure dynamic in the 5-year-old, student , and elderly groups. In the 3-year-old group was there was modest evi dence of the non-stationarity in the time domain being differentially present across frequencies (approx. 10% of trials), These findings are consistent with the proposition that short-term bounded non-stationar ity prevails in quiet upright bipedal stance across a wide range of th e lifespan. This process of non-stationarity may be a reflection of ad aptation in the development of the coordination and control of posture . (C) 1997 Elsevier Science B.V.