Maintaining your position in relation to the center of the earth is something we all take for granted each day as we move about the earth. We are able to do so only because of an extremely complex and Divinely designed system in our bodies called the Vestibular System which contains, in part, the Otolith Organs and the Semi-circular Canals. These organs are sort of like gyros for our bodies, sensing linear and angular movement. The signals they produce are sent to the brain and the brain then processes the information for use in a myriad of tasks. One of these tasks is to help us maintain our balance, another is to maintain retinal stabilization. Retinal stabilization is the object lesson that may give insight into the effectiveness of the overall system.
Basically, the vestibular system holds the eye in place. How can you prove this? Find another person who is open to slight embarrassment and ask them to help you. Move up close to their face and look at the inner details of their eye. Note the small intricacies of the details so you can determine exact position. Now, have them rotate their head on the longitudinal axis (nose to back of head) and note how the eye does not move at all with the moving head. The eye remains in the exact position regardless of head movement. Why does it do so? Because the Vestibular system is holding the eye perfectly still…retinal stabilization!
Another fun test…hold your index finger up in front of you at arms length and move it back and forth side to side. Hold your head perfectly still and track the moving finger with your eyes. Increase the speed of the finger until the finger just begins to blur. Note this speed in your mind. Now, take the same finger and hold it perfectly still in front of you, but move your head on the vertical axis at double the speed you were moving your finger in the earlier test. Note that even though your head is moving twice as fast, the finger remains in perfect focus. Why? Because the vestibular system is employed in the second exercise, while in the first you are moving your eye voluntarily. Bottom line…your vestibular system is able to determine the most minute movements and provide your body with all sorts of inputs to help it remain erect while walking around.
Here’s the rub for aviators…the system works against you in flight! While in flight, linear and angular forces are enacted upon your body by the moving aircraft that incorrectly move the vestibular system and the brain then gives appropriate input to your body parts. One of the body parts that moves is the eye. So, if you were to go on a flight, get into IMC and get some sort of spatial disorientation, not only would your body “lie to you” and, for example, make you feel that you were straight and level when you really were in a turn, your brain would also “bank” your eye. So, not only would you feel the body was out of position, your eye would exasperate the problem by actually banking as well.
Bottom line…a case of spatial disorientation is something that is incredibly dangerous and also something your body is ill-prepared to counter. The very system you rely on each day (and which works nearly flawlessly on the ground) will absolutely lie to to you while flying. Retinal stabilization is one of the easiest ways to see how well the system works on the ground, and how well the system will lie to you while flying. Guard against spatial disorientation by understanding the threat and not being complacent. It can happen to anyone…at least anyone that has a vestibular system.