Every step we take dances on the edge of disaster – one miscalculation at the moment when we are shifting weight from one foot to the other, and we fall. Balance is a sixth sense and a crossmodal perception. It has nothing to do with hearing, but clearly begins with sensors in the inner ear. We call it Equilibrioception.
Our sense of balance depends on the integration of three sensory systems:
- Vision: seeing helps us determine our body’s position in reference to the world (gravity). Note: some blind people have issues with balance
- Proprioception: (see related post) uses the skeletal systems (the muscles and joints and their sensors) to determine the position of the body
- Vestibular system: The section of the inner ear composed of semicircular canal system, which indicate rotational movements; and the otoliths, which indicate linear acceleration.
The vestibular apparatus (shown below) includes the utricle, saccule, and three semicircular canals (Anterior, Horizontal, and Posterior). The utricle and saccule detect gravity (information in a vertical orientation) and linear movement. As we move our heads fluid moves through the canals and tells us the relative position of our head and its movement. The otoliths act as a kind of accelerometer, helping determine the speed of the body or heads movement. The vestibular system then sends signals to the neural structures that control eye movements, and to the muscles that keep an animal upright.
Human balance perception is not quite terrestrial, that is, we certainly have some perceptual systems or strategies that other land animals do not. For example: a human can stand in a bus holding onto a pole and have little or no issues with balance, but a horse standing in a horse trailer has significant problems with the movement of the vehicle, even though it has four legs (four points of stability). We almost certainly owe this extra bit of balance expertise to our ancestors of the trees.
Virtual reality comes to mind again. It should be noted that professional level flight simulators use hydraulic mechanisms to provide a sense of pitch and acceleration by moving entire simulator rooms. Without some feedback of this sort, virtual reality will always be semi-virtual.