Sight is the most important sense in traffic. You receive around 90% of all traffic information through your eyes. For this reason, you are required to have a visual acuity of at least 0.5 for a category B licence (other licence categories have stricter requirements).
If you have poor eyesight, your driving licence may be issued on the condition that you must wear glasses to drive. Also remember that your eyesight changes with age, so you are recommended to have regular eye tests.
The area we see is called the visual field. The visual field has the shape of a semicircle, i.e. 180°.
The thing you focus your eyes on is what you will see most clearly. This is your central vision, and it constitutes approximately 1–2% of your visual field. Central vision is important in order to, for example, make out what is written on a road sign.
The remaining 98–99% of your visual field is your peripheral vision. With it, you can perceive something happening but will most often need to shift your gaze to check with your central vision exactly what it is. The peripheral vision is impaired by alcohol and tiredness.
Semicircle: Visual field
Ö: Location of eye
1: Central vision
2: Peripheral vision
You constantly collect information through your eyes. This information goes to the brain to be interpreted. It is impossible to make profound assessments about everything you see in traffic; the brain would be overloaded.
Instead of assessing everything, the brain quickly selects relevant things to focus on. This selection is made with the help of a number of factors, including your:
If you know from experience that children use to play here, you will be extra careful.
If your knowledge tells you that parked cars can hide pedestrians, and you have experience of children running out in that same spot, your brain will momentarily devote most attention to that aspect.
Terms that may be good to know:
Humans are smart and have a vivid imagination. This is very helpful in traffic. We are able to imagine a probable scenario based on very little information.
However, we sometimes interpret what we see incorrectly, thus creating an optical illusion.
Illustration of the “one-eyed car” optical illusion. It is dark out. A thinks that B is a small and slow moped, as B only has one headlight. A is therefore driving closer to the middle of the road (safer in the dark). When A finally realises that B is a car, they are close to colliding!
Tunnel vision means that your eyes scan a more narrow area. You miss things that happen on the side of the road (in the periphery). It is as if you were driving in a tunnel with dark walls.