Motion induced blindness.

Motion Induced Blindness

A very interesting physiological problem that effects driving as badly as flying:

"This is frightening! It works exactly like it says, and is one major reason people in cars can look right at you (when you're on a motorcycle or bicycle)---AND NOT SEE YOU. From a former Naval Aviator. This is a great illustration of what we were taught about scanning outside the cockpit when I went through training back in the '50s. We were told to scan the horizon for a short distance, stop momentarily, and repeat the process. I can remember being told why this was the most effective technique to locate other aircraft. It was emphasized (repeatedly) to NOT fix your gaze for more than a couple of seconds on any single object. The instructors, some of whom were WWII veterans with years of experience, instructed us to continually "keep our eyes moving and our head on a swivel" because this was the best way to survive, not only in combat, but from peacetime hazards (like a midair collision) as well. We basically had to take the advice on faith (until we could experience for ourselves) because the technology to demonstrate it didn't exist at that time."

Click here for a very illuminating display of this effect:

http://www.msf-usa.org/motion.html