Visibility Conception
Visual information is the most important input to a driver driving a motor vehicle. Any restriction to good visibility increases the danger of accidents, since the reaction of the driver would be delayed. Hence due attention has to be paid in order to reduce the restrictions on visibility as far as possible. Furthermore, the obstruction of vision as a result of instrumentation (tachometer, fuel level indicator, clock etc.) should be avoided, so that the driver is not distracted from the road for a long time.
Human visual ability can be divided into three areas:
          Visual range
          Field of vision
          Field of view.
The visual range covers that area which the resting eye (without head and eye movement) perceives images but not perfectly sharp enough (figure on left). Sharp focus is only possible in the field of view in the form of a cone with an angle of aperture of 4°. The size of the visual range depends on the type of vision. Here, a classification takes place based on how a point in percieved in the visual range:
     Monocular vision: Vision through one eye
     Binocular vision: Vision through both eyes simultaneously
   Ambinocular vision: Vision through one or both eyes (sum of monocular right and monocular left)
If the field of vision is spatially extended in the horizontal plane, asymmetrical areas limited by the eyebrows in the upward direction and by cheeks and nose laterally as well as downwards result (figure on right).
Since the area of sharp vision is limited, eye and head movements are necessary in order to be able to view the field surrounding the vehicle. The area that can be detected only with eye movements and with a resting head position is called the field of vision. There is a consideration of eye as well as head movement in the field of view.