The eye transmits messages to the inner ear mechanism that creates equilibrium. So for example, if the eyes are reading a book and the car ride is bumpy and swervy the messages are contradictory, resulting in motion sickness. The symptoms of motion sickness usually start with uneasiness or discomfort. Then, the person will begin to look pale and green. They will soon feel dizzy or have a headache.
Motion sickness can quickly turn into nausea and vomiting.
The symptoms can last well after a trip is over. Motion sickness is easier to prevent then to cure. A little planning in advance of a trip is a good idea. If you are prone to motion sickness, while riding in a car keep your head still or lay on a pillow. To avoid an imbalance in the inner ear focus on a point in the far distant horizon.