Simple Model of Sensory Interaction in Human Postural Control

Upright body stance is inherently unstable. Active feedback control utilizing motion cues from various sensory systems is necessary in order to maintain this upright position. Visual, somatosensory, and vestibular sensory systems are the main contributors to this feedback control. In many environments, accurate information is available from all three of these sensory systems. In other environments, motion information from one or more sensory systems may be absent or inaccurate leading to poor performance (increased body sway) or falls in extreme cases. However simple observations indicate that the motion information from the three sensory systems is highly redundant in that upright stance can be maintained when orientation cues are absent or inaccurate in two of the three sensory systems. For example, a normal subject can stand with eyes closed on a foam pad suggesting that vestibular cues alone are sufficient to maintain upright stance. Also, a subject with a bilateral vestibular loss can stand on a flat surface with eyes closed indicating that somatosensory cues alone provide sufficient feedback information for postural control.