Direct Vision and Peripheral Vision

Of our entire field of vision, we only see around 1-2 % with full clarity; this is our so-called direct vision or central vision. The remaining part of our field of vision, 98–99% of what we see, is our so-called peripheral vision. Our peripheral vision is not as focused, but can allow us to identify objects in motion. Peripheral vision is impaired by tiredness, alcohol and drugs.

Impairment of Vision

When you apply for your driving licence, you are required to undergo an eye examination. You need a visual acuity of at least 0.5, either naturally or with the help of glasses/contact lenses. If you need glasses or lenses to attain this level of vision, then you must wear these when driving.

If you lose sight in one eye, it can take some time before your vision adjusts. You must therefore wait six months before you can drive again.

Our vision is reduced in the dark since there is not as much light as there is during the day. Some people also experience further visual impairment in the dark. Some people suffer from issues such as nyctalopia or night blindness.

Vision often gets worse with age, and night vision in particular can deteriorate. Visual impairment is often gradual, so it can be difficult to detect. It is therefore important to have your vision tested regularly.

Optical Illusions

Your brain interprets the information that your eyes gather from your surroundings. This process usually works as it should, especially if we are in good form, but sometimes it can go wrong. When certain items of information are missing, our brain completes a full picture and fills in the missing parts itself; this can cause optical illusions.

Example:

• Fog and snow storms can create optical illusions; e.g. in which direction the road turns.

• An oncoming car with only one functioning headlight may appear to be an oncoming motorcycle or moped.

Scanning

What you see corresponds to about 90% of the information you take in when on the road. Scanning is all about how you read traffic situations. Poor scanning can mean that you miss important information and there is a risk that you will only notice dangers when it is too late. This can lead to late reactions which surprise other road users behind you.

Better scanning comes with experience and knowledge. Studies have shown some of the differences in driving styles between newly qualified drivers and their more experienced counterparts:

Newly qualified drivers

• Keep their gaze too close to the car.
• Focus more on stationary objects.
• Are more passive and scan smaller areas.

Experienced drivers

• Keep their gaze further ahead.
• Focus more on moving objects.
• Have a more active gaze.

What you should do:

• Active gaze: If you fix your gaze on one particular object, you will miss other important pieces of information in your surroundings.
• Further away gaze: You should focus your gaze a long way ahead of the car, along the road. This will allow you to plan your driving and detect dangers in good time. It will also make it easier for you to maintain a steady course.
• Eye contact: You should make eye contact to avoid misunderstandings with other road users.

The Brain Selects and Interprets

Our sight provides us with a great deal of information on the road. This information is then processed and interpreted by the brain. The process of using sensory information to develop an awareness of what is happening around you is called perception. The brain is not able to process all the information it receives and must therefore select the most important parts. This is called selective perception.

Judgement of Distance

When an object is within a range of ten metres, we use stereo vision to judge the distance; this requires both eyes. If you lose vision in one eye, it becomes more difficult to judge distance; especially in the beginning when you are still adjusting to the change.

When judging longer distances, we use several different techniques:

• Size: The farther away an object is, the smaller the object will appear to be.
• Perspective: The road looks narrower farther away. Verge reflector posts at the side of the road will appear closer together and the distance between posts will seem shorter.
• Obstructing objects: If a tree obscures our view of a house, then we know that the tree is closer to us than the house is.
• How clearly an object appears: If an object seems blurred, it will seem like it is farther away. When visibility is reduced, such as when it is raining or foggy, for example, it becomes more difficult to judge distances. Objects might seem further away than they really are.

Judging Speed and Oncoming Vehicles

Studies have shown that it is very difficult to judge the speed of other vehicles, even for experienced drivers.

It is particularly difficult to judge the speed of oncoming vehicles. This means that it is easy to make mistakes when passing an oncoming vehicle. If the oncoming vehicle is travelling at a faster speed than you, your cars will pass each other sooner than expected.

Because it can be so difficult to judge exactly when you will pass oncoming vehicles, you should always drive carefully when you overtake vehicles on roads with oncoming traffic. Maintain a good safety distance and abandon any overtakes that become risky!

Other Senses Used When Driving

Hearing

• If you hear that your engine is in overdrive, you know that is necessary to switch to a lower gear.
• You get used to how your engine sounds. If it starts to sound differently, this may because there is something wrong.
• Other vehicles can warn you by beeping their horn.

Sense of touch

• If you feel that the car is pulling to one side, this may be due to the wheel alignment or a lack of air in the front tires.
• If you are driving at too high a gear, you may feel that the engine begins to hack or that the car accelerates poorly.

Sense of smell

• If there is anything wrong with your engine or brakes, or if you are driving with the parking brake on, you may notice a burning smell.
• Your sense of smell will also help you notice if there are any exhaust fumes in the car.

Sense of balance

• Your sense of balance allows you to feel when you are accelerating or braking.
• If you are sitting in the right position, you may even be able to feel that you are about to skid.