[Effects of eye tracking stimulation on movements of the body's center of gravity and the head in elderly subjects (second report)].

This study was designed to investigate the effects of eye movement (smooth pursuit and saccade) on the upright standing postural control, and to compare movements of the body's center of gravity (CG) and the head between an elderly group and a young control group. The elderly group consisted of 28 healthy subjects aged 60 to 79 years, the young control group of 11 healthy subjects aged 20 to 39 years. Visual conditions consisted of fixation on a spot fixed target, pursuit of a 0.1 Hz sinusoidally horizontally moving target and fixation on a 0.1 Hz alternately changing right and left target. The parameters analyzed were total lengths of the locus traced by CG and head movement, the area which was a multiplication of maximum widths in the X and Y directions, ratio of the antero-posterior component to the lateral component (Y/X ratio), averaged divisional frequencies calculated in the range between 0.0195 and 1 Hz, and the ratio of head movement to CG movement regarding total lengths and area. The results were as follows: 1) Body sways in the elderly and young groups were similarly affected by eye movements. The results suggest that inputs from the extraocular muscles produce an asymmetry in the tonus of antigravity muscles and an increase in lateral body sway, and that different visual conditions elicit different sensations of perturbation, which cause characteristic postural responses. 2) Head movement was relatively larger than CG movement in the elderly group.(ABSTRACT TRUNCATED AT 250 WORDS)