Actually there is some vision science behind this phenomenon. Your fovea is what you use to focus on things and it's got lots of cone cells that are good at picking up colors and specific details but are not so good at picking up motion. The rest of your eye though has tons of rod cells that effectively see just black and white, but are really good at doing motion detection (mainly to recognize predators and prey in your peripheral vision). So instead of trying to use your fovea to find the plane (which it really sucks at doing), you instead keep your eye moving which exposes much more of the scene to rod cells and let their natural motion detection abilities go to work.
> Only a small part of the retina, in the centre and called the fovea, can generate a high-resolution image. This is why we need to look directly at something, by moving our eyes, to see detail. The rest of the retina contributes to our visual experience by adding the peripheral detail — hence peripheral vision. Peripheral vision cannot resolve detail, which prevents the brain from being overloaded with too much information, but it is very good at detecting movement.
> Well, first, it is an unfortunate fact that if you are converging on a given point with another vehicle at the same speed, and assuming that you are both traveling in a straight line, then there is no apparent movement noticeable by the occupant of either vehicle. That is, to the driver of each vehicle, the other will remain in exactly the same position in the windscreen up to the point of impact. There is no relative movement — so our peripheral vision is not suited to detecting it.
> Now for the really interesting part. When we move our head and eyes to scan a scene, our eyes are incapable of moving smoothly across that scene and seeing everything. This makes perfect sense: just like trying to take a picture without holding the camera still. The image would be blurred. So, our clever brain overcomes this by moving our eyes (really fast, remember) in a series of jumps (called saccades) with very short pauses (called fixations and it is only during the pauses that an image is processed. Our brains fill in the gaps with a combination of peripheral vision and an assumption that what is in the gaps must be the same as what you see during the pauses.
