The effect of light finger touch on reducing postural sway has been widely replicated; however, the mechanism of this effect has not been well understood. While the sensory hypothesis states that sensory stimuli available from light finger touch is used to automatically diminish postural sway, the suprapostural task hypothesis argues that posture is adjusted by the demand imposed by the precision requirements of light finger touch. The object of this study was to test the sensory and the suprapostural task hypotheses. Thirty-four adults kept quiet standing while lightly touching a stable plate using index finger with various touch forces (very light touch and light touch), and precision demands (low and high demand). Consistent with the sensory hypothesis, postural stability was significantly greater with light touch as compared to very light touch, as greater touch force results in greater amount of sensory stimuli. Also, consistent with the suprapostural task hypothesis, postural stability was significantly increased under high precision rather than low precision demand conditions. The current results indicated that both hypotheses were valid, suggesting that the sensory and the suprapostural task effects can coexist for adaptive control of postural sway, and in various scenarios, one is dominant over another.
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